Curso Directional Drilling II log

COMPUTALOG DRILLING SERVICES

Directional Drilling II Training Tr aining Curriculum CRCM_240_revA_0110

E

T

H N

C

O L O

. 2 0 0 S T

E

G

0

P

S

E R

Y

V I

U

O

C E S G R

Computalog Drilling Services Technology ogy Services Group 16178 West Hardy Road, Houston, Texas 77060 Telephone: 281.260.5700 281.260.5700 Facsimile: 281.260.5780 281.260.5780

This page intentionally left blank.

Directional Drilling II - 5 Days Prerequisites : Directional Drilling I Course Content

Survey / Toolface (Offset) Accuracy & Quality Control Well Planning (Wellz) Project Ahead Survey / Toolface (Offset) Accuracy & Quality Control Students will differentiate between mechanical sensor failures, unstable gravity values, and magnetic interference effects by analyzing survey data and quality control plots.

Magnetic Corrections Earth’s Magnetic Field Magnetic Declination Applying Declination Correction Grid Corrections Magnetic North True North Grid North GEOMAG / MRIP / GEODEC Output to be used by field engineer Job Geomagnetic Sheet GEOMAGENTIC Reference Maps Example Problems Surface Parameters & Processing Survey (Hole Position) Processing Flowchart Surface Survey Parameters Grid Corrections Downhole Survey Parameters Toolface Offset Measurement Positive Pulse toolstring Negative Pulse toolstring EM toolstring Toolface Offset Entry Positive Pulse toolstring Negative Pulse toolstring EM toolstring Paperwork Example

Survey Parameter Analysis Real-Time Report Example “Validating a Survey Probe Response” (Using Excel Spreadsheet) Real-Time Report Parameters Gtotal Gx, Gy, Gz Bx, By, Bz MWD Surface Roll Test Rotational Checkshots Algorithm Uncertainty Downhole Data QC for Field Engineers Surveying methods Survey System Accuracy Comparison Accuracy Limitations (electronic vs. mechanical) Independent Survey Comparisons Benchmark Survey Checkshot Survey Rotational Checkshots Gyro or Singleshot Survey Sensor Response & Quality Hardware Failure “Hard” Failure (saturation, no response) “Soft” Failure (sticking, calibration drift, wrong compass, film, batteries) Gravity Values Unstable Rotational Movement During Survey Axial Movement During Quality Control Check (Goxy vs. Gz vs. Gtotal) Magnetic Values Unstable Natural Occurrences (solar flares, northern lights, local anomalies) anomalies) Cross-axial Magnetic Interference (“fish”, casing) Axial (Drillstring) Magnetic Interference (improper NMDC spacing) Drilling in Northern Latitudes (high inclination, E-W direction) Quality Control Check (Boxy vs. Bz vs. Btotal) Other Factors Affecting Survey Accuracy Incorrect Inputs into Software (MFS, DIP, Total Correction) BHA Misalignment in Borehole Real-time MWD Transmission Resolution Predicting Uncertainty Errors (Spreadsheet) “Possible Azimuth Error Charts”

WELL PLANNING (WELLZ)

Generate Simplified Proposal from given parameters Instructor Demonstrates Students use Example #1 Students use Example #2 Edit Elevation Depth from given Well Plan Instructor Demonstrates Students use Example #1 Students use Example #2 Edit Target Depth from given Well Plan Instructor Demonstrates Students use Example #1 Students use Example #2 Compare Survey Reports, Proposed vs. Actual Well Plan Survey Realtime Report Survey Editing Data Entry & Hole Position Report Instructor Demonstrates Students use Example #1 Students use Example #2 Memory/Realtime Survey Report Determine Possible Uncertainty of Actual Well Well (excel spreadsheet)

PROJECT AHEAD

Bottom Hole Assemblies Principle Configurations Rotary Slide Design Principles Side forces Fulcrum Principle Weight on Bit Well Path vs. Well Plan Interpolate Instructor Demonstrates Students use Example #1 Students use Example #2 Extrapolate Instructor Demonstrates Students use Example #1 Students use Example #2 Build Rate to Top of Target Center of Target Bottom of Target Instructor Demonstrates Students use Example #1 Students use Example #2 Desired Toolface Setting to Intersect Target Instructor Demonstrates Students use Example #1 Students use Example #2

Computalog

MAGNETIC DECLINATION CONTENTS WHAT IS MAGNETIC DECLINATION? Do compasses point to the north magnetic pole? If unlike poles attract, then why doesn't the north tip of a compass point magnetic south? HOW DO I COMPENSATE FOR DECLINATION AND INCLINATION? Declination adjustment Arithmetic compensation Maps with magnetic meridians Inclination compensation for specific latitude zones WHAT FACTORS INFLUENCE DECLINATION? (What is the precision of a compass?) Location Local magnetic anomalies Altitude Secular change Where were/are/will be the magnetic poles? Diurnal change Solar magnetic activity "Bermuda Triangle" type anomalies HOW DO I DETERMINE THE DECLINATION DIAGRAMS ON MAPS? Declination diagrams on maps Grid north and declination diagrams Isogonic charts Declinometer REFERENCES AND ACKNOWLEDGMENTS

Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without t he expressed written consent of Computalog. Magnetic Declination.doc

8/29/00

1-1

Doc. # TD2003.rev A

Computalog

MAGNETIC DECLINATION Many people are surprised to learn that a magnetic compass does not normally point to true north. In fact, over most of the Earth it points at some angle east or west of true (geographic) north. The direction in which the compass needle points is referred to as magnetic north, and the angle between magnetic north and the true north direction is called magnetic declination. You will often hear the terms "variation", "magnetic variation", or "compass variation" used in place of magnetic declination, especially by mariners. The magnetic declination does not remain constant in time. Complex fluid motion in the outer core of the Earth (the molten metallic region that lies from 2800 to 5 000 km below the Earth's surface) causes the magnetic field to change slowly with time. This change is known to as secular variation. An an example, the accompanying

diagram shows how the magnetic declination has changed with time at Halifax. Because of secular variation, declination values shown on old topographic, marine and aeronautical charts need to be updated if they are to be used without large errors. Unfortunately, the annual change corrections given on most of these maps cannot be applied reliably if the maps are more than a few years old since the secular variation also changes with time in an unpredictable manner. If accurate declination values are needed, and if recent editions of the charts are not available, up-to-date values for Canada may be obtained from the most recent geomagnetic reference field models produced by the Geological Survey of Canada.

The elements iron, nickel and cobalt possess electrons in their outer electron shell but none in the next inner shell. Their electron "spin" magnetic moments are not canceled, thus they are known as ferromagnetic.


8/29/00

1-2

Doc. # TD2003.rev A

Computalog Earth's core has remained molten due to heat from ongoing radioactive decay. Convection currents of molten rock containing ferromagnetic material flow in the earth’s outer core generating a magnetic field. The magnetic poles of this field do not coincide with true north and south poles (the axis of rotation of the Earth).

In mid 1999, the average position of the modeled magnetic north pole

(according to the IGRF-2000 geomagnetic model) is 79.8° N, and 107.0° W, 75 kilometers (45 miles) northwest of Ellef Ringnes Island in the Canadian Arctic. This position is 1140 kilometers (700 miles) from the true (geographic) north pole. At the magnetic poles, the Earth's magnetic field is perpendicular to the Earth's surface. Consequently, the magnetic dip, or inclination (the angle between the horizontal and the direction of the earth's magnetic field), is 90°. And since the magnetic field is vertical, there is no force in a horizontal direction. Therefore, the magnetic declination, the angle between true geographic north and magnetic north, cannot be determined at the magnetic poles.


8/29/00

1-3

Doc. # TD2003.rev A

Computalog The geomagnetic field can be quantified as total intensity, vertical intensity, horizontal intensity, inclination (dip) and declination. The total intensity is the total magnetic field strength, which ranges from about 23 microteslas (equivalent to 23000 nanoteslas or gammas, or 0.23 oersteds or gauss) around Sao Paulo, Brazil to 67 microteslas near the south magnetic pole near Antarctica.


8/29/00

1-4

Doc. # TD2003.rev A

Computalog Vertical and Horizontal intensity are components of the total intensity.


8/29/00

1-5

Doc. # TD2003.rev A

Computalog


8/29/00

1-6

Doc. # TD2003.rev A

Computalog The angle of the magnetic field relative to the level ground (tangent to the earth) is the inclination, or dip, which is 90° at the magnetic north pole and 0° at the magnetic equator.


8/29/00

1-7

Doc. # TD2003.rev A

Computalog Finally, the angle of the horizontal intensity with respect to the true north (geographic) pole is the declination, also called variation in mariners' and aviators' jargon. In other words, declination is the angle between where a compass needle points and the true North Pole.

If the compass needle points west of true north, this offset is designated as west declination. The world standard, including in the southern hemisphere, is in reference to the magnetic north (MN) declination. In the context of astronomy or celestial navigation, declination has a different meaning. Along with right ascension, it describes the celestial coordinates of a star, etc. Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without t he expressed written consent of Computalog. Magnetic Declination.doc

8/29/00

1-8

Doc. # TD2003.rev A

Computalog Do compasses point to the north magnetic pole? Most people incorrectly believe that a compass needle points to the north magnetic pole. But the Earth's magnetic field reacts to the effect of complex convection currents in the magma, which must be described as several dipoles, each with a different intensity and orientation, the compass actually points to the sum of the effects of these dipoles at your location. In other words, it aligns itself with the local magnetic field lines of force. Other factors, of local and solar origin, further complicate the resulting local magnetic field. It may be all right to say that a compass needle points "magnetic north" but it only roughly points to the magnetic north pol e. The table below compares examples of actual and incorrect declinations (using IGRF95 model for 1998.0, anomalies ignored).

Long.

Actual Declination (degrees) (angle between where a compass needle points and true north pole)

Model Declination Error (degrees) (degrees) (angle between north magnetic dip pole and true north pole)

Location

Lat.

Sydney Australia Anchorage USA Buenos Aires Argentina Montreal Canada Los Angeles USA Perth Australia Rio de Janeiro Brazil St. Petersburg, Russia Ostrov Bennetta New Siberian Islands

34.0S 151.5E

13 E

13 E

00

61.5N 150.0W

23 E

20 E

03

34.5S 058.0W

06 W

09 W

03

45.5N 073.5W

16 W

10 W

06

34.0N 118.5W

14 E

03 E

11

32.0S 116.0E

02 W

09 E

11

23.0S 043.0W

21 W

10 W

11

60.0N 030.5E

08 E

12 W

20

77.0N 148.0E

11 W

33 E

44

If unlike poles attract, then why doesn't the north tip of a compass point magnetic south?


8/29/00

1-9

Doc. # TD2003.rev A

Computalog Should we be calling the north magnetic pole, the southern magnetic pole of the Earth, or should we be referring to the south magnetized needle of the compass as pointing magnetic north? Neither. A compass needle is a magnet and the north pole of any magnet is defined as the side which points magnetic north when the magnet is freely suspended; its correct title is "north seeking pole," but it has unfortunately been shortened to "north pole."

Maps label the magnetic pole in the northern

hemisphere as the "North Magnetic Pole". The cardinal points were defined long before the discovery that freely suspended magnets align to magnetic north. When some curious person placed lodestone (magnetite) on wood floating on water, or floated it directly on mercury, it was observed to align in a consistent direction, roughly pointing north. The side of the lodestone that pointed magnetic north was called, naturally, the "north pole". But that was before it was realized that like poles of magnets repel. So we must now make the distinction that the real north pole is the Earth's north magnetic pole, and the poles of all magnets that (roughly) point to it are north seeking poles.

HOW DO I COMPENSATE FOR DECLINATION AND INCLINATION? Since magnetic observations are neither uniformly nor densely distributed over the Earth, and since the magnetic field is constantly changing in time, it is not possible to obtain up-to-date values of declination directly from a database of past observations. Instead, the data are analyzed to produce a mathematical routine called a magnetic reference field "model", from which magnetic declination can be calculated.

Global models are produced every one to five years. These constitute the series of International Geomagnetic Reference Field

(IGRF)

models.

The

World

Magnetic Model Epoch 2000 (WMM2000), models. The latest IGRF and WMM model was produced in 2000, and is valid until 2005. The Canadian Geomagnetic Reference Field (CGRF) is a model of the magnetic field over the Canadian region. It was produced using denser data over Canada than were used for the IGRF, and Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without t he expressed written consent of Computalog. Magnetic Declination.doc

8/29/00

1-10

Doc. # TD2003.rev A

Computalog because the analysis was carried out over a smaller region, the CGRF can reproduce smaller spatial variations in the magnetic field than can the IGRF. The latest CGRF was also produced in 2000 and is valid until 2005. The accompanying declination chart is based on the CGRF. Since magnetic field models such as the WMM, IGRF and CGRF are approximations to observed data, a value of declination computed using either of them is likely to differ somewhat from the "true" value at that location. It is generally agreed that the WMM and IGRF achieves an overall accuracy of better than 1° in declination; the accuracy is better than this in densely surveyed areas such as Europe and North America, and worse in oceanic areas such as the south Pacific. The accuracy of the CGRF, in southern Canada, is about 0.5°. The accuracy of all models decreases in the Arctic near the North Magnetic Pole. Magnetic field models are used to calculate magnetic declination by means of computer programs such as the Magnetic Information Retrieval Program (MIRP), a software package developed by the Geomagnetism Program of the Geological Survey of Canada. The user inputs the year, latitude and longitude and MIRP calculates the declination. MIRP is able to compute values for any location on the Earth in the time period 1960 to 2000. For locations within Canada, MIRP computes values using the CGRF. Outside Canada, values are calculated using the IGRF. Below is an example of a Geomagnetic software package used to calculate many magnetic parameters. Inputs required for this example are Latitude, Longitude, Elevation, Date and Model. Output we would normally use are Magnetic Field Strength (Incident Field), Magnetic Dip angle (Dip) and Magnetic Declination (Dec). Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without t he expressed written consent of Computalog. Magnetic Declination.doc

8/29/00

1-11

Doc. # TD2003.rev A

Computalog

WHAT FACTORS INFLUENCE DECLINATION? Location Each position on the Earth has a particular declination. The change in its value as one travels is a complex function.

If a navigator happens to be traveling along a rather straight line of equal

declination, called an isogonic line, it can vary very little over thousands of kilometers. However; for one crossing isogonic lines at high latitudes, or near magnetic anomalies, the declination can change at over a degree per kilometer (6/10 mile).

Local magnetic anomalies Predictive geomagnetic models such as the World Magnetic Model (WMM) and the International Geomagnetic Reference Field (IGRF) only predict the values of that portion of the field originating in the deep outer core. In this respect, they are accurate to within one degree for five years into the future, after which they need to be updated. The Definitive Geomagnetic Reference Field (DGRF) model describes how the field actually behaved. Local anomalies originating in the upper mantle, crust, or surface, distort the WMM or IGRF predictions. Ferromagnetic ore deposits; geological features, particularly of volcanic origin, such as faults and lava beds; topographical features such as ridges, trenches, seamounts, and mountains; ground that has been hit by lightning; downhole features such as casing, stuck bottom hole assemblies, drill string and bottom hole assemblies can induce errors of three to four degrees. Anomalous declination is the difference between the declination caused by the Earth's outer core and the declination at the surface.

It is illustrated on 1:126,720 scale Canadian topographic maps

published in the 1950's, which included a small inset isogonic map. On this series, it is common to observe a four-degree declination change over 10 kilometers (6 miles), clearly showing local anomalies. There exist places on Earth, where the field is completely vertical; where a compass attempts to point straight up or down. This is the case, by definition, at the magnetic dip poles, but there are other locations where extreme anomalies create the same effect. Around such a place, the needle on a standard compass will drag so badly on the top or the bottom of the capsule, that it can never be steadied; it will drift slowly and stop on inconsistent bearings. While traveling though a severely anomalous region, the needle will swing to various directions.


8/29/00

1-12

Doc. # TD2003.rev A

Computalog A few areas with magnetic anomalies (there are thousands more): -North of Kingston, Ontario; 90° of anomalous declination. -Kingston Harbor, Ontario; 16.3° W to 15.5° E of anomalous declination over two kilometers (1.2 miles); magnetite and ilmenite deposits. -Near Timmins, Ontario, W of Porcupine. -Savoff, Ontario (50.0 N, 85.0 W). Over 60° of anomalous declination. -Michipicoten Island in Lake Superior (47.7 N, 85.8 W); iron deposits. -Near the summit of Mt. Hale, New Hampshire (one of the 4000-footers, near the Zealand Falls hut on the Appalachian Trail) ; old AMC Guides to the White Mountains used to warn against it. -Around Georgian Bay of Lake Huron. -Ramapo Mountains, northeastern New Jersey; iron ore; compass rendered useless in some areas. -Near Grants, New Mexico north of the Gila Wilderness area; Malpais lava flows; compass rendered useless. The USGS declination chart of the USA (GP-1002-D) shows over a hundred anomalies. The following table lists the most extreme cases. Anomalous (Lat. declination degrees) 46.4 W 40.2 24.2 E 40.7 16.6 E - 12.0 W 46.7 14.8 E 33.9 14.2 E 45.5 13.8 W 45.7 13.7 E 48.4 13.5 E 48.5 13.0 W 42.2 12.2 W 38.9 11.5 E 47.8

Long.

Location

106.2 75.3 95.4 92.4 82.7 87.1 86.6 122.5 118.4 104.9 92.3

75 km.(45 mi.) W Boulder, Colorado 20 km. (12 mi.) NE Allentown, Pennsylvania 250 km. (150 mi.) NW Minneapolis, Minnesota 85 km. (50 mi.) S Little Rock, Arkansas In Lake Huron, Ontario Escanaba, on shore of Lake Michigan In Lake Superior, Ontario 80 km. (50 mi.) N Seattle, Washington In Alvord Desert, Oregon 10 km. (6 mi.) W Colorado Springs, Colorado 120 km. (75 mi.) N Duluth, Minnesota

In 1994, the average location of the north magnetic dip pole was located in the field by the Geological Survey of Canada. This surveyed north magnetic dip pole was at 78.3° N, 104.0° W, and takes local anomalies into consideration. However; the DGRF-90 modeled magnetic dip pole for 1994 was at 78.7° N, 104.7° W. The 47-kilometer (29 mile) difference illustrates the extent of the anomalous influence. In addition to surveyed dip poles and modeled dip poles, a simplification of the field yields geomagnetic dipole poles, which are where the poles would be if the field was a simple EarthConfidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without t he expressed written consent of Computalog. Magnetic Declination.doc

8/29/00

1-13

Doc. # TD2003.rev A

Computalog centered dipole. Solar-terrestrial and magnetospheric scientists use these. In reality, the field is the sum of several dipoles, each with a different orientation and intensity.

Distortion caused by cultural features is called deviation. Altitude (Negligible to 2 degrees) This factor is normally negligible. According to the IGRF, a 20,000 meter (66,000 foot) climb even at a magnetically precarious location as Resolute, 500 kilometers (300 miles) from the north magnetic pole, would result in a two-degree reduction in declination.

Secular change (2-25 years/degree)

Where were/are/will be the magnetic poles? As convection currents churn in apparent chaos in the Earth's core, all magnetic values change erratically over the years. The north magnetic pole has wandered over 1000 kilometers (600 miles) since Sir John Ross first reached it in 1831, as shown on this map at SARBC (extend the path to north west of Ellef Ringes Island for 1999), or this map at USGS. Its rate of displacement has been accelerating in recent years and is currently moving about 24 kilometers (15 miles) per year, which is several times faster than the average of 6 kilometers (4 miles) per year since 1831. The magnetic pole positions can be determined more precisely by using a calculator that returns magnetic inclination. Latitudes and longitudes can be entered by trial and error, until the inclination (I) is as close as possible to 90°. North Magnetic Pole Movement 1945-2000


8/29/00

1-14

Doc. # TD2003.rev A

Computalog South Magnetic Pole Movement 1945-2000

A given value of declination is only accurate for as long as it stays within the precision of the compass,

preferably one degree. Typical

secular change or variation (do not confuse with mariners' and aviators' variation) is 2-25 years per degree. A map that states: "annual change increasing 1.0' " would suggest 60 years per degree, but that rate of change just happened to be slow on the year of measurement, and will more than likely accelerate. The

magnetic

field

has

even

completely

collapsed and reversed innumerable times, which have been recorded in the magnetic alignment of lava as it cooled. One theory to explain magnetic pole reversals is related to large meteorite impacts, which could trigger ice ages. The movement of water from the oceans to high latitudes would accelerate the rotation of the Earth, which would disrupt magmatic convection cells into chaos. These may reverse when a new pattern is established. Another theory is that the reversals are triggered by a slight change the angular momentum of the earth as a direct result of the impacts.

These theories are challenged by the controversial Reversing Earth Theory, which

proposes that the entire crust could shift and reverse the true poles in a matter of days, but that the molten core would remain stationary, resulting in apparent magnetic reversal. The Sun would then rise in the opposite direction.

Diurnal change (negligible to 9 degrees) The stream of ionized particles and electrons emanating from the Sun, known as solar wind, distorts Earth's magnetic field. As it rotates, any location will be subject alternately to the lee side, then the windward side of this stream of charged particles. This has the effect of moving the magnetic poles around an ellipse several tens of kilometers in diameter, even during periods of steady solar wind without gusts. The Geological Survey of Canada shows a map of this daily wander or diurnal motion in 1994. Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without t he expressed written consent of Computalog. Magnetic Declination.doc

8/29/00

1-15

Doc. # TD2003.rev A

Computalog The resulting diurnal change in declination is negligible at tropical and temperate latitudes. For example, Ottawa is subject to plus or minus 0.1 degree of distortion. However; in Resolute, 500 kilometers (300 miles) from the north magnetic pole, the diurnal change cycles through at least plus or minus nine degrees of declination error. This error could conceivably be corrected, but both the time of day and the date would have to be considered, as this effect also varies with seasons.

Solar magnetic activity (negligible to wild) The solar wind varies throughout an 11-year sunspot cycle, which itself varies from one cycle to the next. In periods of high solar magnetic activity, bursts of X-rays and charged particles are projected chaotically into space, which creates gusts of solar wind. These magnetic storms will interfere with radio and electric services, and will produce dazzling spectacles of auroras. The varied colors are caused by oxygen and nitrogen being ionized, and then recapturing electrons at altitudes ranging from 100 to 1000 kilometers (60 to 600 miles). The term "geomagnetic storm" refers to the effect of a solar magnetic storm on the Earth (geo means Earth. The influence of solar magnetic activity on the compass can best be described as a probability. The chance that the declination will be deflected by two degrees in southern Canada over the entire 11year cycle is 1% per day. This implies about four disturbed days per year, but in practice these days tend to be clustered in years of solar maxima. These probabilities drop off rapidly at lower latitudes. During severe magnetic storms, compass needles at high latitudes have been observed swinging wildly.

"Bermuda Triangle" type anomalies (very rare) Legends of compasses spinning wildly in this area of the Atlantic, before sinking a ship, or blowing up an airplane, may be related to huge pockets of natural gas suddenly escaping from the ocean floor. As the gas bubbles up, it could induce a static charge or could ionize the gas, which would create erratic magnetic fields. The gas would cause a ship to lose buoyancy, or a plane flying through a rising pocket of natural gas could ignite it. The ionized gas may show as an eerie green glow at night. It could make people feel light headed and confused because the gas replaces the air, but it would not have the mercaptans that gas companies add to gas to give it its distinctive odor.


8/29/00

1-16

Doc. # TD2003.rev A

Computalog At enormous pressures and low temperatures (as at the bottom of the sea), water and gas molecules form gas hydrates. These compounds resemble ice but, unlike ordinary ice, the water molecules form cages that trap gas molecules such as methane. The solid hydrates retain their stability until conditions, such as higher temperatures or lower pressures, cause them to decompose. The gas may remain trapped under silt, until an earthquake triggers a release. This phenomenon is not restricted to the "Bermuda Triangle". The insurance statistics at the Lloyds of London have not revealed an unusual number of sunken ships in the triangle.

HOW DO I DETERMINE THE DECLINATION DIAGRAMS ON MAPS? Most topographic maps include a small diagram with three arrows: magnetic north, true north and Universal Transverse Mercator grid north. The given value of declination, corresponding to the center of the map, does not take local anomalies into account. The value is usually out of date, since it may have drifted several degrees due to secular change, especially on maps of remote regions with several decades between updates. Some maps, such as the 1:50,000 scale topographic maps by the Canadian Department of Energy, Mines and Resources include the rate of annual change, which is useful for predicting declination, but that rate of change is erratic and reliability of the forecast decreases with time. A rate of change over five years old is unreliable for one-degree precision. The United States Geological Survey's 1:24,000 scale maps do not even mention annual change. For example, the approximate mean declination 1969 on the Trout River, Newfoundland map was 28° 33' west with annual change decreasing 3.0'. This implies a recent (1997) value of: 28° 33' - ((1997-1969) * 3.0) = 27° 93' but IGRF 1995 for 1997 yields 23° 44', which is 3° 25' less, showing that the 28-year prediction was in significant error.

Grid north and declination diagrams (negligible to 2 degrees) Grid north is the direction of the north-south lines of the Universal Transverse Mercator (UTM) grid, imposed on topographic maps by the United States and NATO armed forces. UTM Provides a constant distance relationship anywhere on the map. In angular coordinate systems like latitude and longitude, the distance covered by a degree of longitude differs as you move towards the poles and Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without t he expressed written consent of Computalog. Magnetic Declination.doc

8/29/00

1-17

Doc. # TD2003.rev A

Computalog only equals the distance covered by a degree of latitude at the equator.

With the advent of

inexpensive GPS receivers, many other map users are adopting the UTM grid system for coordinates that are simpler to use than latitude and longitude. The problem with grid north is that is coincident with true north only at the center line of each UTM zone, known as central meridians. The difference between grid north and true north can be over two degrees.

This might not be so bad if it were not for the different conventions with respect to

declination diagrams adopted by different countries. A declination diagram on a topographic Canadian map or an Australian map shows magnetic north with respect to grid north, but a US map shows magnetic north with respect to true north.

Therefore, if you use declination from a

Canadian/Australian style declination diagram, be sure to take bearings to and from the map by making the meridian lines on the compass parallel with the UTM grid (grid north). However, if you use declination from a USGS style declination diagram or any of the other sources below, you must make the meridian lines on the compass parallel with the edges of the map (true north). Canadian maps show a blue fine-lined UTM grid, while some USGS 1:24,000 scale maps show black grid lines, but the others only show blue grid tick marks on the map margins. The choice of grid lines or tick marks on the US maps seems inconsistent by year or by region.

Printed Isogonic charts Isogonic or declination charts are plots of equal magnetic declination on a map, yielding its value by visually situating a location, and interpolating between isogonic lines. Some isogonic charts include lines of annual change in the magnetic declination (also called isoporic lines). Again, the older, the less valid. The world charts illustrate the complexity of the field. A Brunton 9020 compass included a 1995 isogonic chart of North America, on a sheet copyrighted in 1992 The 1:1,000,000 scale series of World Aeronautical Charts include isogonic lines. Hydrographic charts include known magnetic anomalies. The McGraw-Hill Encyclopedia of Science and Technology (1992 edition) provides a small world chart under "geomagnetism." The best is the 1:39,000,000 Magnetic Variation chart of "The Earth's Magnetic Field" series published by the Defense Mapping Agency (USA). The 11th edition is based on magnetic epoch 1995.0 and includes lines of annual change and country borders. Ask for Geophysical Data Chart Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without t he expressed written consent of Computalog. Magnetic Declination.doc

8/29/00

1-18

Doc. # TD2003.rev A

Computalog stock No. 42 (DMA stock No. WOBZC42) at a National (USA) Ocean Service navigation chart sales agent or order from the NOS Distribution Division, about US$10. Size: 1.26 X 0.9 meters (50" X 35"). It covers from 84° N to 70° S. North and south polar areas are on Geophysical Data Chart stock No. 43 (DMA stock No. WOBZC43). European marine chart distributors may have better availability for the 1:45,000,000 scale "The World Magnetic Variation 1995 and Annual Rates of Change" chart published by the British Geological Survey. However; it lacks country borders. Ask for No. 5374, about US$16. A 1:48,000,000 world declination chart of "The Magnetic Field of Earth" series is published by the United States Geological Survey's Earth Sciences Information Center. However; the most recent edition is still based on magnetic epoch 1990.0. It does include lines of annual change and country borders. Look it up at a university map library or order GP-1004-D from the United States Geological Survey. Only US$4.00 (+ US$3.50 for shipping and handling). Size 1.22 X 0.86 meters (48" X 34"). Includes polar regions at 1:68,000,000 scale. A United States declination chart is also published. Scale 1:5,000,000 (Alaska and Hawaii 1:3,500,000), epoch 1990.0, GP-1002-D, US$4.00 + US$3.50 S&H, 1.14 X 0.8 meters (45" X 34"), includes over 100 magnetic anomalies.

On-line Isogonic charts North America 1990, Others 1995: South America, Europe, Middle East, Southeast Asia, Australia/New Zealand, Global: Ricardo's Geo-Orbit Quick Look satellite dish site World, small: United States Geological Survey World, larger, color, 1995: National (USA) Geophysical Data Center or Stanford University in California World, slightly more readable, 1995: National (USA) Geophysical Data Center World, black and white, 1995, seven magnetic parameters, including polar projections: Kyoto University in Japan World, color, 1995, five magnetic parameters and their rates of secular change, click to zoom. USA Department of Defense Canada, CGRF95: Geological Survey of Canada Canada, more detailed (caution: outdated--1985): Search and Rescue Society of British Columbia United States, 1995, small, three magnetic parameters (note: longitudes are in 360° format): United States Geological Survey


8/29/00

1-19

Doc. # TD2003.rev A

Computalog Mexico, IGRF95: Instituto de Geofísica, Universidad Nacional Autónoma de México. The blue lines are declination, and the red lines are annual change. Australia, AGRF95 for 1997.5: Australian Geological Survey Organization (AGSO) Finland, 1998.0: Finnish Meteorological Institute. It has wavy isogones in an attempt to include magnetic anomalies from the Earth's crust. Generate your own: Kimmo Korhonen at the Helsinki University of Technology, Finland wrote this Java applet in which you specify a region and date. Great idea, but the maps lack detail.

On-line and downloadable declination data Use an atlas to find your latitude and longitude before you can use the links below. Pangolin in New Zealand features a Java applet that continuously returns magnetic variation as the pointer is moved over a map of the world. Sorry, no zooms available, but it computes great circle bearings and distances. http://www.pangolin.co.nz/magvar.html Geological Survey of Canada: declination http://www.geolab.nrcan.gc.ca/geomag/e_cgrf.html National (USA) Geophysical Data Center: seven magnetic parameters and their rates of secular change. http://www.ngdc.noaa.gov/cgi-bin/seg/gmag/fldsnth1.pl Interpex Limited: GEOMAGIX freeware http://geomag.usgs.gov/Freeware/geomagix.htm

can

be

downloaded.

Defense Mapping Agency: GEOMAG freeware can be downloaded. ftp://ftp.ngdc.noaa.gov/Solid_Earth/Mainfld_Mag/DoD_Model/Basic_Software/dmabasic.exe Ed William's Aviation page: Geomagnetic Field and Variation Calculator freeware can be downloaded in Mac, Linux, and DOS versions and are suitable for batch processing. http://www.best.com/~williams CBU Software: MAGDEC shareware (30-day trial) provides a plot of declination vs. years, latitude or longitude and will transform bearings from one year to another. It covers USA only, from 1862 to present. http://www.datacache.com/descript.htm

Declinometer/Inclinometer A declinometer/inclinometer is sophisticated instrument makes precision measurements of declination and inclination. It is used to calibrate compasses or to periodically calibrate continuously recording variometers in magnetic observatories. The angle at which its electronic fluxgate magnetometer reads a minimum value, is compared to a sighting through its optical theodolite.

True north is

determined by sighting a true north reference target mounted some distance away, or is derived from celestial navigation calculations on a sighting of the sun or another star.


8/29/00

1-20

Doc. # TD2003.rev A

Computalog

Link to references and acknowledgments.

Questions, comments, corrections, and additions are welcome. Please E-Mail me in French or English at [email protected] [email protected].. Copyright 1997-1999 by Chris M. Goulet.. Updates of this FAQ will be posted at: Communications Accessibles de Montreal http://www.cam.org/~gouletc/decl_faq.html and at:Geocities http://www.geocities.com/Yosemite/Gorge/8998/decl_faq.html

Disclaimer (Lawyer Repellent): Permission is hereby granted to apply the information in this document on the condition that be author not be held responsible nor liable for any damages.

Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced reproduced electronically or used for any purpose without t he expressed written consent of Computalog. Magnetic Declination.doc

8/29/00

1-21

Doc. # TD2003.rev A


Computalog

Directional Drilling Azimuth Reference Systems

This paper discusses the primary azimuth reference systems currently used in directional drilling. This will include True North and Magnetic references with particular detail given to Grid Coordinate systems (i.e. UTM, UTM, Lambert, Geographic, Geographic, and Local). A simple field-proven method is also presented to help avoid confusion when converting from one system to another.

More than one multi-million dollar directional drilling project has missed its intended target(s) due to errors and/or misunderstandings surrounding the azimuth reference system in use. The confusion arises primarily from the necessity to change from one system to another between the well planning phase, where most maps are drawn with respect to a local Grid North, and the drilling phase where surveying is performed with respect to a Magnetic or True North reference. The field company representative is faced with a confusing array of possible conversions, including declination corrections from Magnetic North to True North, True North to Grid North, Magnetic to Grid North, or Grid to Magnetic North. Is the correction to be added or subtracted from the survey measurement? Is the convergence magnitude magnitude and sign correct correct for the grid grid system used? With all these questions, it is easy to see why this this seemingly simple task is is often performed improperly and the mistake not realized until the target is missed.

The rig

foreman often passes on the responsibility convergence the

for

field

application

service

to

company

supplying the surveys or to the directional driller. While this

practice

may

appear

sound in theory, it usually creates additional confusion as basic information is often poorly

communicated

misconstrued.

It

is

or not

uncommon that on projects where

several

service

Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced reproduced electronically or used for any purpose without the expressed written consent of Computalog. Az Ref Systems.doc

8/30/00

2-1

Doc. # TD2002.rev A

Computalog companies perform different surveys (i.e. MWD, single shots, multi-shots, and gyros) that each supplier comes up with a different convergence value.

A case in point involved a recent high high visibility multi-million dollar directional directional drilling project. In this this incident, a well known well planning company drew the well maps with respect to the local grid coordinate system, with a footnote stipulating that the directional contractor would be responsible for grid and magnetic declination convergence. When the operation began, the rig site was manned by a company representative, two consulting drilling engineers, and a directional driller all responsible for deviation control. The directional company was not accustomed to deriving grid corrections and solicited solicited help from the company representative. representative. He assumed the local grid was UTM (later learned to be state plane) and the appropriate UTM convergence was applied. He then had the directional company’s office redraw the well maps rotated by that UTM correction. The office complied and added in the the magnetic declination as well. The directional driller missed this fact, however, and continued to apply a declination correction at the rig site as drilling continued.

It was not until the project was

completed and the target missed that the errors were realized.

This project was more closely supervised than a normal directional well, yet it serves as a classic example of how easily the relative relationships between coordinate systems can be poorly communicated and inappropriately inappropriately applied. The remainder of this paper will examine methods to reduce these azimuth convergence errors by utilizing

field

experience

and

suggested

communication procedures between all involved parties.

AZIMUTH REFERENCES

Azimuth, (AZ) used in directional drilling, may be defined as the direction of the wellbore (at a given point) projected into the horizontal plane measured in a clockwise direction from Magnetic North, True North North or Grid North after after applying a North Reference system. system. Azimuth should be Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced reproduced electronically or used for any purpose without the expressed written consent of Computalog. Az Ref Systems.doc

8/30/00

2-2

Doc. # TD2002.rev A

Computalog o

expressed as a value on a 0°-360 compass

system.

Quadrant

or

bearing systems (i.e. N45° 20’E) may be easier to visualize, but make the probability of convergence mistakes higher than than in an azimuth system. It is therefore recommended to have all survey printouts converted to an azimuth system when making initial convergence directional

corrections. drilling

and

For borehole

surveying, there are three primary azimuth

references.

Magnetic

North

They (MN),

are True

(Geographic) North (TN), and Grid North (GN).

Magnetic North is the direction of the horizontal component of the earth’s magnetic field lines at a particular point on the earth’s earth’s surface pointing to the magnetic pole. A magnetic compass will will align itself to these lines with with the positive pole of the compass indicating indicating North. Magnetic North is usually symbolized on maps by a half arrow head or the letters MN.

True or Geographic North is the horizontal direction from a point on the earth’s surface to the geographic North Pole, which which lien on the earths axis of rotation. rotation. The direction is shown shown on a globe by meridians of longitude. True North i.e. normally symbolized on maps by a star at the tip of the arrow or the letters TN.

Grid North is a reference system devised by map markers in “the complicated task of transferring the curved surface of the earth onto a flat sheet. The meridians of longitude on a globe converge toward the North Pole and therefore do not produce a rectangular grid system. A map can be drawn such that the grid lines are rectangular, for some specified area of the earth, the northerly direction of which is determined by one specified meridian of longitude. This direction is called Grid North and is identical to True North only for that specified central meridian. It is normally symbolized on a map by the letters “GN” at the tip of the arrow.


8/30/00

2-3

Doc. # TD2002.rev A

Computalog

GRID SYSTEMS

Geographic coordinates. One of the oldest systematic methods of location is based upon the geographic coordinate system. While this information is basic, a short review is included for reference. By drawing a set of east-west rings around the globe (parallel to the equator), and a set of north- south rings crossing the equator at right angles and converging at the poles, a network of reference lines is formed from which any point on the earth’s surface can be located. The distance of a point north or south of the equator is known as latitude. The rings around the earth parallel to the equator are called parallels of latitude or simply parallels. Lines of latitude run


8/30/00

2-4

Doc. # TD2002.rev A

Computalog east-west, with north-south distances measured between them. A second set of rings around the globe at right angles to lines of latitude and passing through the poles are known as meridians of longitude or simply meridians. One meridian is designated as the prime meridian. The prime meridian accepted by the majority of the world runs through Greenwich, England, and is known as the Greenwich meridian. The distance east or west of a prime meridian to a point is known as longitude. Lines of longitude (meridians) run north-south, with east-west distances measured between them. Geographic coordinates are expressed angular measurement. Each circle is divided into 360°, each degree into 60 minutes, and each minute into 60 seconds. The degree is 0

symbolized by ( ), the minute by (’), and the second by (‘’). Starting with 0° at the equator, the parallels of latitude are numbered to 90° both north and south. The extremities are the North Pole at 90° north latitude and the South Pole at 90° south latitude. Latitude can have the same numerical value north or south of the equator, so the direction N or S must always be given. It can also be further defined as Geographic/Geodetic or Geocentric Latitude. Geodetic is the angle that a line perpendicular to the surface of the earth makes with the plane of the equator. It is slightly greater in magnitude than the Geocentric latitude, except at the equator and poles where it is the same due to the earth’s ellipsoidal shape. The Geocentric latitude is the angle made by a line to the center of the earth at the equatorial plane.

Starting with 0° at the prime meridian, longitude is measured both east and west around the world. Lines east of the prime meridian are numbered to 0° to +180° and identified as east longitude: lines west of the prime meridian are numbered to 0° to -180° and identified as west longitude. The direction E (+) or W (-) must always be given. The line directly opposite the prime meridian, 180°, may be referred to as either east or west longitude.

Geographic Datum. For most atlas maps and any directional drilling map, the earth may be considered a sphere. Actually it more nearly resembles an oblate ellipsoid flattened by approximately one part in three hundred at the poles due to rotation. On small scale maps this oblateness is negligible. However, different ellipsoids will produce slightly different coordinates for the same point on the earth and therefore warrant a brief summary.

Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without the expressed written consent of Computalog. Az Ref Systems.doc

8/30/00

2-5

Doc. # TD2002.rev A

Computalog More than a dozen principal ellipsoids have been measured in the past two hundred years which are still in use by one or more countries. An official shape was designated in 1924 by the International Union of Geodesy and Geophysics (IUGG) and adopted a flattening ratio of exactly one part in 297. This was called the International Ellipsoid and was based on Hayford’s calculations in 1909 giving an equatorial radius of 6,378,388 meters and a polar radius of 6,356,911,9 meters. Many countries did not adopt this ellipsoid however, including those in North America. The different dimensions of the other established ellipsoids are not only the result of varying uncertainties in the Geodetic measurements that were made, but also are due to a nonuniform curvature of the earth’s surface due to irregularities in the gravity field. It is for this reason that a particular ellipsoid will be slightly more accurate in the areas it was measured, rather than using a generalized ellipsoid for the whole earth. This also includes satellite derived ellipsoids such as WGS72. The table below illustrates some of the official ellipsoids in use today.

Equatorial Radius,a,

PolarRadius

Flattening

Name

Date

Meters

b, metere

f

Use

GRS 19802

1980

6,378,137

6,356,752.3

1/298.257

Newly adopted

WGS 723

1972

6,378,135

6,356,750.5

1/298.26

NASA

Australian

1965

6,378,160

6,356,774.7

1/298.25

Australia

Krasovaky

1940

6,378,245

6,356,863.0

1/298.25

SovietUnion

Internat’1

1924

6,378,388

6,356,911.9

l/297

Remainderof the”world

Hayford

1909

6,378,388

6,356,911.9

1/297

Renainderof the world

Clarke

1880

6,378,249.1

6,356,514.9

1/293.46

Most of Africa;France

Clarke

1866

6,378,206.4

6,356,583.8

1/294.98

North America; Philippines

Map Projections. A map projection is a method of transferring part or all of a round body on to a flat sheet. Since the surface of a sphere cannot be represented accurately on a flat sheet without distortion the cartographer must choose characteristics he wishes to display precisely at the expense of others.

There is consequently no best method of projection for map making in

general. Different applications require different projections.


8/30/00

2-6

Doc. # TD2002.rev A

Computalog Some characteristics normally considered in choosing a particular projection are: true shape of physical features, equal area, true scale and size, great circles as straight lines, rhomb (compass point) lines as straight lines, and correct angular relationships. A map of relatively small size, such as a directional well path, will closely achieve most

or

all

of

these

characteristics with any method of projection.

Map

projections

are

generally classified with respect to their method of construction accordance

in with

the

developable surface from which they were devised, the most common being cylindrical, conical, and planer.

An examination of these projections shows that most lines of latitude and longitude are curved. The quadrangles formed by the intersection of these curved parallels and meridians are of different sizes and shapes, complicating the location of points and the measurement of directions. To facilitate these essential operations, a rectangular grid maybe superimposed upon the projection.

Universal Transverse Mercator Grid (UTM). The most common worldwide grid system used in directional drilling is the UTM.

The U.S. Army adopted this

system in 1947 for designating rectangular coordinates on large scale military maps of the entire world. The UTM is based on the Cylindrical Transverse Mercator Conformal Projection, developed by Johann Lambert in 1772, to which specific parameters have been applied, such as central meridians. Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without the expressed written consent of Computalog. Az Ref Systems.doc

8/30/00

2-7

Doc. # TD2002.rev A

Computalog

The UTM divides the world into 60 equal zones (6° wide) between latitude 84°N and latitude 80°S. Polar regions are normally covered by a separate planer projection system known as Universal Polar Stereo-graphic. Each of the 60 zones has its own origin at the intersection of its central meridian and the equator. The grid is identified in all 60 zones. Each grid is numbered, beginning with zone 1 at the 180th Meridian, International Date Line, with zone numbers increasing to the east. Most of the North America is included in Zones 10-19. Each zone is flattened and a square grid superimposed upon it.

Any point in the zone may be referenced by citing its zone number, its distance in meters from the equator (“northing”) and its distance in meters from a north-south reference line (’easting”). These three components: the zone number, easting and northing make up the complete UTM Grid Reference for any point, and distinguish it from any other point on earth. The Figure below shows a zone, its shape somewhat exaggerated, with its most important features. Note that when drawn on a flat map, its outer edges are curves, (since they follow meridian lines on the globe), which are farther apart at the equator than at the poles.

UTM zones are sometimes further divided into grid sectors although this is not essential for point identification. These sectors are bounded by quadrangles formed every 8° in latitude both north and south and are designated by letters starting with C at 80° South to X at 72° North, excluding I and O.

Dallas for

example is in grid zone 14s covering a quadrangle from 96° to 102°W and from 32° to 40°N.

Sectors may be further

divided into grid Squares of 100,000 meters on a side with double letter designations including partial squares of 10,000 meters, 1,000 meters and 100 meters designated by numbers and letters. Confidential and Proprietary information of Com putalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without the expressed written consent of Computalog. Az Ref Systems.doc

8/30/00

2-8

8

Doc. # TD2002.rev A

Computalog

The two most important features of the zones are the equator, which run east and west through its center, and the central meridian. Easting and northing measurements are based on these two lines. The easting of a point represents its distance in meters from the central meridian of the zone in which it lies. The northing of a point represents its distance in meters from the equator.

By common agreement, there are no negative numbers for the castings of points west of the central meridian. Instead of assigning a value of 0 meters to the central meridian of each zone, each is assigned an arbitrary value of 500,000 meters, increasing to the east. Since along the equator at their widest points, the zones somewhat exceed 600,000 meters from west to east, easting values range from approximately 200,000 meters to approximately 800,000 meters at the equator, with no negative values. The range of possible casting values narrows as the zones narrow toward the poles. Northings for points north of the equator are measured directly in meters, beginning with a value of zero at the equator and increasing to the north. To avoid negative northing values for points south of the equator, the

equator

is

arbitrarily

assigned a value of 10 million meters,

and

points

are

measured with decreasing, but positive, northing values heading southward.

Some

maps,

particularly in the U.S., have converted UTM coordinates from meters to feet.

In

utilizing

the

Transverse

Mercator Projection, the central UTM meridian has been reduced in scale by 0.9996 of True to minimize variation in a given zone.

This scale factor (grid

distance/true distance) changes Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without the expressed written c onsent of Computalog. Az Ref Systems.doc

8/30/00

2-9

Doc. # TD2002.rev A

Computalog slightly as you move away from the central meridian and should be considered if very accurate measurements are desired. However, this error is very small in directional drilling maps and is usually ignored.

Approximately 60 countries use the UTM as the most authoritative and general use projection within the world, although some also use secondary local projections and grid references.

The

Russia, China and other European countries use the Transverse Mercator (Gauss-Kriiger)

with

6°

zones.

Approximately 50 countries use other projections.

Lambert Conformal Conic

Projection. The Lambert System is based on a conformal conic projection and is particularly useful in mapping regions that have a predominately eastwest expanse. This system has heavy use in North America and is the official U.S. state plane coordinate system for more than half of the 48 contiguous states, including the majority of those where oil is drilled and produced (i.e. Texas, Louisiana, Oklahoma, California, Colorado, Kansas, Utah, and Michigan). The remainder of the states, including Wyoming, uses the Transverse Mercator with Alaska using a combination.

This projection was first described by Lambert in 1772, but received little use until the First World War where France revived it for battle maps. The features of this conic projection include: •

Parallels of latitude are unequally spaced arcs of concentric circles

•

Meridians of longitude are equally spaced radii cutting the parallels at right angles

•

Scale is normally true along two defined parallels, but can be true along one

•

Pole in same hemisphere is a point, other pole is at infinity


8/30/00

2-10

Doc. # TD2002.rev A

Computalog Since there is no distortion at the parallels, it is possible to change the “standard parallels” to another pair by changing the scale applied to the existing map and recalculating standards to fit the new scale. Each state or area has it’s own standard parallels, or sets of the same depending on its size, to reduce distortion at the center. For example, Louisiana is divided into three zones as shown in the Table below. Zone

STANDARD PARALLELS

ORIGIN

Long.

Lat.

North

31° 10* N 32° 40t N

92° 301 w 30° 401 N

South

29° 18’ 3C” 42* 91° 201 28° 40’

Offshore

26° 10’ 27° 501

91° 201 25° 40’

The grid origins for most states are measured in feet, with the east-west axis starting at 2,000,000 feet and the north-south axis set at 0 feet.

Local Grid systems. There are numerous local grid systems in use around the world today. These systems all have different base line coordinates and projections, covering different sizes of surface areas, but all serve the same basic purpose as outlined for UTM and Lambert. In the U.S. lease lines often are used as a convenient grid reference, as well as other privately surveyed grids. Outside the U.S., local grids are used in Holland, the U.K., Brunei, Australia, and other countries. Several countries have also shifted the starting of the UTM grid zones to fall inside their own territory.

In some situations when using standard grid coordinates, the well’s target location may lie in a different zone from the surface location. In these cases creating a nonstandard zone normally produces a special local grid. This is done by either extending the surface location zone by a few miles to include the target, or shifting the zone center, as sometimes is done with UTM, 3° to the zone boundary.


8/30/00

2-11

Doc. # TD2002.rev A

Computalog

AZIMUTH REFERENCE SYSTEM CONVERSIONS

Most well proposals are generated from rectangular coordinates derived from the UTM or local grid system. The surface location to target direction will therefore be referenced to Grid North. Since wells must be surveyed with sensors that reference direction to either Magnetic or True North, it will be necessary to convert between these references.

Magnetic

Declination

Correction.

Magnetic

declination correction converts azimuth values between the Magnetic North and True North systems. declination

The

magnetic

correction

is

the

angle between the horizontal component

of

the

earth’s

magnetic field lines and the lines of longitude. When Magnetic North lies to the west of True North, the magnetic declination is said to be westerly, and if to the east, easterly.

Values of magnetic declination change with time and location. Magnetic Declination models are updated every year. Their values and rates of change can be obtained from Computer programs like GEOMAG or “world magnetic variation charts” or “isogonic charts” which are issued by all major hydrographic institutes in the world once every five years (1980, 1985, ’90, etc.). Computer programs like GEOMAG use current magnetic models and calculate up-to-date local declination figures. The most accurate method to determine local declination is to measure the magnetic field with a magnetic transit.

When

magnetic

results

are

recorded, the declination and the date must be included. Local values of magnetic declination


8/30/00

2-12

Doc. # TD2002.rev A

Computalog O

should be stated in the well program to plus or minus 0.1 .

Grid Correction Angle. A grid correction converts azimuth readings between the True North systems and the specified grid system.

The angle of correction is the angle between the

meridians of longitude and the Northings of the grid system at a specified point. The magnitude of the correction angle depends upon its location within the grid and its latitude. The closer the point is to the grid central meridian and to the equator, the smaller the correction.

The computation of the grid correction angle or angle of convergence will require special mathematical techniques depending on the type of projection of the curved earth’s surface on to the flat grid.

The directional software packages will at minimum handle UTM and Lambert

conformal conic convergence. The chosen sign convention displays Grid North as “x” number of degrees east or west of True North. For example, when you convert the geographic coordinates latitude N 30° 00’ 00” and longitude W 95° 00’ 00” to UTM coordinates (using the Hayford International - 1924 Ellipsoid), the computer will display the following results: UTM Coordinates: Hemisphere = North Zone = 15 Northing = 3320517.348 Easting = 307077.096 Grid Convergence = W 1° 0’ 0”

o

This listing indicates a grid convergence of 1 00’ 00”. Grid convergence as calculated by the directional software package is the angular difference in degrees between True North and UTM Grid North. UTM Grid North is said to be “X” number of degrees either east or west of True North.

When working with the UTM system, the calculated direction between two UTM

coordinates is referenced to Grid North. To convert this UTM Grid North direction to a True North direction, you must apply the grid convergence to the calculated UTM Grid North direction. This sign convention is not necessarily the same for all contractors and should be clearly communicated and understood before drilling begins.


8/30/00

2-13

Doc. # TD2002.rev A

Computalog System Conversions. Once accurate magnetic declination and grid convergence angles are acquired, all that is needed to change reference systems is to add or subtract these angles from one another. While this seems a simple task, misunderstandings surrounding the relationship between these references can cause a target to be missed.

To avoid this confusion,

declination/grid conversion polar diagrams should be drawn on all maps and clearly defined on al l survey printouts. With this in mind, the following procedure is suggested: 1.

Convert quadrant/bearing readings, including declination and grid convergence, to a 0360 degrees azimuth system.

2.

Draw a polar diagram showing True North at 0 degrees azimuth (12 o’clock).

3.

Draw an arrow for Magnetic North using an exaggerated angle east or west of True North showing the declination angle (east declination is east of True North and west is west).

4.

Draw an arrow for Grid North using an exaggerated angle east or west of True North showing the grid convergence angle (be sure of the sign convention of the grid convergence value used, for example does a west convergence angle put Grid North west of True North or visa versa?).

5.

Draw an arrow pointing east (azimuth of 90°) for an arbitrary borehole azimuth reference.

6.

Label the borehole azimuth with reference to each system.

True North azimuth will equal 90°; Magnetic azimuth will equal 90° plus/minus declination; Grid azimuth will equal 90° plus/minus grid convergence. With these three references it is a simple matter to determine whether declination and/or convergence need to be added or subtracted to switch from one system to the other.

Example one depicts a situation with a 3.0 west grid convergence and a 5.0

o

o

declination. The diagram clearly shows the arbitrary True North azimuth of 90

o

east magnetic to equal 93.0

o

o

Grid North reference and 85.0 Magnetic North reference. To convert from Magnetic azimuth to True azimuth add 5.0

o

to all Magnetic North azimuths and so forth. The chart adjacent to the

polar diagram shows all possible combinations to change between systems. The survey printout should include, under an azimuth reference heading, the following data: 1) Grid North is 3.0°W (CCW) from True North; 2) Magnetic North is 5.0° (CW) from True North and 8.0°E (CW) from Grid North, December 1987; and 3] Survey printout is referenced to Grid North. Example two depicts a similar situation with a 3.0° east grid convergence and an 8.0° east magnetic declination. Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without the expressed written consent of Computalog. Az Ref Systems.doc

8/30/00

2-14

Doc. # TD2002.rev A

Computalog

COMMUNICATION

Accurate communication, both written and oral, is the key to avoiding convergence errors. This function can generally be divided into two or three groups depending on the size of the organization and the complexity of the project.

The initial group will normally consist of seismic crews, geophysical and geology departments, who will be responsible for developing structure maps and choosing targets with respect to a common coordinate system. The next group might be land/hydrographic survey crews, geology, drilling engineering, and a directional service company who might be responsible for developing well plans to the proposed targets from selected surface locations.

At this point the grid

convergence and magnetic declination angle should be computed, cross checked, and documented on the well prognosis and directional maps using a polar grid convergence diagram. All groups should be in agreement with these values before release to operations. The final group might consist of drilling engineering, operations drilling foremen, and directional drillers who will be responsible for drilling the well to target as planned. This is the stage where most errors and miscommunication are likely to occur. Never assume the man on the rig will understand your written communications. A meeting should be held, at the rig site if necessary, to assure that all parties understand the map azimuth reference and the magnitude and sense of necessary correction angles.

CONCLUSION

A missed target for any reason can be a financial disaster; a missed target for azimuth reference convergence error is inexcusable. This mistake can be avoided by: •

TRAINING responsible personnel basic grid systems, magnetic declination, convergence angle corrections, and use of polar grid convergence diagrams.


8/30/00

2-15

Doc. # TD2002.rev A

Computalog

•

COMMUNICATION, both written and oral, of azimuth references and conversion corrections to all responsible parties from geophysics to geology to drilling engineering to operations to directional drilling contractors.

•

PROFESSIONAL SUPERVISION provided by drilling engineering, operations drilling superintendents, rig foremen, and directional drilling contractors.

NOMENCLATURE

GN Grid North MN Magnetic North TN True North UTM Universal Transverse Mercator Grid System x, y Equatorial Earth’s Radius z Polar Earth’s Radius

REFERENCES 1.

Synder, John P.: Map Projections Used by the U.S. Geological Survey, United States Government Printing office, Washington, D.C. (1982) Page 15

2.

Synder, John P.: Map Projections Used by the U.S. Geological survey, United States Government Printing Office, Washington D.C. (1982) page 60.

3.

Gillan, C. and Wadsworth D.: “Automated Drilling Data Provides Instant Insights into Complex Problems” American Oil and Gas Reporter

BIBLIOGRAPHY

1.

Judson, Sheldon, and Left, Don L.: Physical Geology, Prentice-Hall, Inc, Englewood Cliffs, New Jersey, (1965)

2.

Englewood Cliffs, New Jersey, (1965) & Piloting, Naval Institue Press, Annapolis, Maryland (1985) Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without the expressed written consent of Computalog. Az Ref Systems.doc

8/30/00

2-16

Doc. # TD2002.rev A

Computalog 3.

Synder, John P.: Map Projections Used by the U.S. Geological Survey, United States Government Printing office, Washington, D.C. (1982)


8/30/00

2-17

Doc. # TD2002.rev A

Coordinate Systems

Coordinate Systems Geographic Coordinates

One of the most accurate means of depicting a point on the earth’s surface is by referring to its geographic coordinates. The earth, as a sphere, is divided into theoretical lines (or meridians) of longitude (running from pole to pole) and parallels of latitude (running parallel to the equator). The meridians of longitude run 180° east and west of 0° (running through Greenwich). The parallels of latitude run 90° north and south of the equator (0° latitude). In this way, any point on the earth's surface can be referred to by its latitude and longitude. While this system is very accurate for defining the position of a point with reference to the center of the earth, it becomes quite an involved process to refer two points to each other and to represent them in two dimensions.

EARTH

Parallels of Latitude

P

ß ø Point: P can be expressed in terms of degrees of Latitude: ß and degrees of Longitude: ø

2-18

Meridians of Longitude

Universal Transverse Mercator System

Universal Transverse Mercator System In the UTM System, the world is divided up into 60 equal zones (each 6 ° wide) between 80° north and 80° south; polar regions are covered by other special projections. Each zone has its own origin at the intersection of its central meridian and the equator. Each zone is flattened and a square imposed on it. Thus, its outer edges are curved when drawn on a flat map since they follow the meridian lines on the globe. Each of the 60 zones is numbered, starting with zone 1 at the 180th meridian. The areas east and west of the Greenwich Meridian are covered by zones 30 and 31. Any point on the earth may be identified by its zone number, its distance in meters from the equator (northing) and its distance in meters from a north south reference line (easting). Zones are sometimes divided into sectors representing intervals of 8 ° latitude, starting with zone C at 80° S and ending with zone X at 72° N (omitting I and O). It is not essential to use the grid sector letter to identify the position of a point on the globe. To avoid negative values for eastings, the central meridian in any zone is assigned the arbitrary eastings value of 500,000 meters. Along the equator a zone is about 600,000 meters wide, tapering towards the polar region. Eastings range in value from approximately 200,000 to 800,000. For points north of the equator, northings are measured directly in meters, with a value of zero at the equator and increasing toward the north. To avoid negative northing values in the Southern Hemisphere, the equator is arbitrarily assigned a value of 10,000,000 meters and displacements in the southern hemisphere are measured with decreasing, but positive, values as one heads south. TRUE NORTH

# NORTHERN HEMISPHERE #

#

H T R O N D I R G

H T R O N D I R G

NORTHERN HEMISPHERE #

N IA ID R E M

EQUATOR L A R T N E C

#

SOUTHERN HEMISPHERE

2-19

#

E H U T R R T O N

SOUTHERN HEMISPHERE

UTM System

UTM System Convergence is the difference between grid north and true north. Clearly, at the central meridian, grid north equals true north. Convergence will vary with distance away from the central meridian and with distance away from the equator.

TRUE NORTH GRID NORTH

GRID NORTH

(West of True North)

(East of True North)

GRID PROJECTION LATITUDE

90°

80°

70° 60° 50° 40° 30°

LONGITUDE

20°

10°

0° E

R T O A E Q U

100° 90°

CENTRAL MEDIAN True North = Grid North

2-20

80° 70°

60°

50°

40°

30°

20°

10°

0°

UTM System continued

UTM System continued The well proposal is usually derived from coordinates in a grid system and, therefore, directions will be in terms grid north. However, the well surveys will use sensors that reference either magnetic or true north, the user must, therefore, be able to convert from one reference to the other. True North Grid North

Corrected Borehole Azimuth

ß ø

Grid Convergence is ß°West True Azimuth is Ø° Grid Azimuth is (Ø + ß)°

Magnetic Declination Correction

Magnetic Declination Correction is the angle between magnetic north and true north. Values of magnetic declination change with time and location. As the movement of magnetic north is constant and predictable, magnetic declination can be calculated for any given point on the earth at any given time. Charts depicting the various declinations and rate of change (usually expressed as an annual change) are widely used. An easterly declination is expressed as a positive value and a westerly declination is expressed as a negative value. Although converting from one reference to another appears a simple task, considerable care is needed, depending on the relative directions of convergence and magnetic declination. True North Magnetic North

Hole Direction

ß

Magnetic Declination is ß°West Magnetic Hole Direction is Ø° Corrected Hole Direction is (ß - Ø)°

2-21

ø

Leaseline or Boundaries

Leaseline or Boundaries In some countries, oil and gas leases are sold. These leases are normally administered by local governing bodies or agencies and have clearly defined boundaries. Any point within a lease can be defined in terms of distance from any two adjoining boundaries.

Northern Boundary

SURFACE LOCATION

y r a d n u o B n r e t s e W

o y t r c e j T r a d e o s p o r P

E a s t e r n B o u n d a r y

TARGET

Southern Boundary

Hardlines

Lines drawn on the plot which should not be crossed for geological and legal reasons.

Land Locations

Planning a directional well presupposes some limiting factors in the positioning of the surface location. With land wells, the surface locati on of the well will usually be determined by the factors originally prompting the decision to drill a directional well as opposed to a vertical well.

Offshore Locations

The main difference between positioning a surface location on land and offshore is that offshore directional programs tend to be drilled from multiwell structures and are not normally as restricted as on land (mountains, jungles, cities, etc.). In most cases, an offshore drilling rig can be placed anywhere above a reservoir. The decision concerning the placement of the surface structure tends to be more affected by reservoir management considerati ons than geographic necessity.

2-22

Bottomhole Targets

Bottomhole Targets Geological Requirements

The first step in planning any well is to define the objective(s). A directional well can have one or more objectives: 

Geological structures

•

Coring points

•

Geological features (such as faults or pinch outs)

•

Other wellbores (as with relief well drilling)

•

Combination of these

In this section, we look at the way in which targets are defined. As we have seen, there are various means of referring to a surface location (UTM, geographic, etc.). The same is true for the target location with the addition of the vertical depth of the target. Partial Coordinates

When planning and drilling a well, it is simpler to use partial coordinates when referring to the target. This involves using the surface location as a reference point (surface reference point) and attributing this point with the value 0,0. All other coordinates can then be referred back to this point, thus simplifying calculation and plotting procedures. The Surface Reference Point (SRP) is usually the rotary kelly bushing, the wellhead or the platform reference point. Once the exact location of the surface reference point and the target are known, the partial coordinates can easily be determined. Normally, these are either rectangular or polar.

North

SURFACE LOCATION

Rectangular Coordinate: East Polar Coordinates A z im u th

D e p a r t u r e

Rectangular Coordinate: South TARGET

2-23

East

Bottomhole Targets

Bottomhole Targets

North

SURFACE LOCATION

Rectangular Coordinate: East

East

Polar Coordinates A z im u th

D e p a r t u r e


Rectangular

Rectangular coordinates are usually given in feet/meters north or south and east or west of the SRP. They can easily be derived by subtracting the UTM coordinates of the SRP from those of the target. For example: N/S (feet)

E/W (feet)

UTM Coordinates Target

62,354,500.00 N

5,262,744.00 E

UTM Coordinates Surface

-62,355,000.00 N

-5,262,544.00 E

Partial Coordinates

-500.00

200.00

A positive value denotes north or east; a negative value denotes south or west. The target in the above example is 500 feet south (-ve) and 200 feet east (+ve) of the SRP.

2-24

Bottomhole Targets

Bottomhole Targets

North

SURFACE LOCATION


East

Polar Coordinates A z im u th

D e p a r t u r e


Polar

Polar coordinates are derived from the rectangular coordinates and are expressed as a distance (departure) and a direction (either quadrant or azimuth). These are derived from the rectangular (or Cartesian) coordinates as follows: Azimuth = tan-1( E/W Coord ÷ N/S Coord ); or, in this case: tan-l( 200 ÷ 500 ) = 21.8° As we know, the target is south and east of the surface reference point, we know the direction of the target from the rig is: S 21.80 E in quadrant format or 158.2° Azimuth Departure = 538.5

2

2

( E/W Coord + N/S Coord ) , or in this case: =

2

2

( 200 + 500 ) =

We can refer to our target in polar coordinates being 538.5 feet (or meters) at Azimuth 158.2°.

2-25

Bottomhole Targets

Bottomhole Targets Target Size

During the drilling phase of a directional well, the trajectory of the wellbore in relation to the target is constantly monitored. Often, costly decisions have to be made in order to ensure that the objectives of the well are met. A well-defined target is essential in making these decisions. The technology available today allows us to drill extremely accurate wells. The cost of drilling the well is largely dependent on the accuracy required, so the acceptable limits of the target must be well-defined before the well is commenced. Cost versus accuracy is the key consideration. In many cases, operating companies adopt an arbitrary in-house target size (or radius of tolerance), particularly in multiwell projects. The size of the target radius often reflects the convention rather than the actual geological requirements of the well. It is common for specific restrictions or hard lines to be specified only when they depict critical features such as: •

Fault lines

•

Pinch outs

•

Legal restrictions

•

Lease line boundaries

Many directional wells have been unnecessarily corrected or sidetracked in order to hit a target radius which, in fact, did not represent the actual objective of the well.

2-26

HOW TO DETERMINE MUD PULSE & EM TOOLFACE OFFSETS

3-1

Toolface Offset Determination

NEGATIVE PULSE OFFSET TOOL FACE OFFSET TOOL FACE (OTF) SHEET This sheet is possibly the most important form that must be filled out correctly. All other work and activity performed by the MWD Operator means naught if the well must be plugged back with cement because of an incorrect OTF calculation (or the correct OTF not being entered into the TLW 2.12 software). Ensure that the OTF calculation is correct, entered into TLW 2.12 correctly and verified by the Directional Driller. The procedure for measuring the OTF is as follows: 1. Measure in a clockwise direction the distance from the MWD high side scribe to the motor high side scribe. Record this length into the OTF work sheet as the OTF distance. In the following example, this value is 351 mm. 2. Measure the circumference of the tubular at the same location where the OTF distance is being measured. Record this length into the OTF work sheet as the Circumference of Collar. 3. Calculate the OTF angle using the following formula: OTF Angle=

OTF Distance x 360 Collar Cirumference

From the above example, if the collar circumference is 500 mm, OTF Angle= (351/500) x 360 = 0.702 x 360 = 252.72o A sample form is as follows:

3-2

Toolface Offset Determ ination

NEGATIVE PULSE OFFSET TOOL FACE (O.T.F. MEASUREMENT) Well Name:

Enter in the Well Name here

Date: Enter in date OTF taken

LSD: Enter in the LSD here

Time: Enter in time OTF taken

Job #: Enter in the MWD job number here

Run #: Enter in the run number

TOP VIEW OF MWD

MWD SCRIBE

PROPER DIRECTION OF OTF

MEASUREMENT

MOTOR SCRIBE (HIGH SIDE)

O.T.F. Distance (Anchor Bolts to Collar Scribe):

351 mm

Circumference of Collar:

500 mm

O.T.F. Angle (Distance / Circumference) x 360:

252.72 degrees

O.T.F Angle entered into Computer as:

252.72 degrees

O.T.F. Distance measured by:

Both MWD Operator Names

O.T.F. Calculated by:


O.T.F Entered into computer by:


O.T.F. Measurement and calculation Witnessed by: Name(s)

3-3

Directional Driller(s)


NEGATIVE PULSE OFFSET TOOL FACE

252.72

3-4


POSITIVE PULSE Toolface Offset INTERNAL TOOL FACE OFFSET (TFO) SHEET Note: For the positive pulse MWD, the OTF is zero . Ensure that a zero OTF has been entered into TLW 2.12. The positive Tool Face Offset (TFO) sheet entries are as follows: 1. Positive Puls e Pulser Set to High Side / Directional Driller: Enter the names of the MWD Operator and Directional Driller respectively. 2.Positive Pulse T.F.O. from PROGTM: Enter the T.F.O. value reported from the high side tool face calibration from TLW 2.12. TFO internal toolface offset

3-5

Toolface Offset Determ ination

POSITIVE PULSE T.F.O. MEASUREMENT Well Name:

Enter in the Well Name here

Date: Enter in date OTF taken

LSD: Enter in the LSD here taken

Time: Enter in time OTF

Job #: Enter in the MWD job number here number

Run #: Enter in the run

ROTATE PULSER TO HIGH SIDE

PULSER KEY WAY

PROPER DIRECTION OF TFO

MEASUREMENT

DAS HIGH SIDE TAB

Positive Pulse Pulser Set to High Side:

Name of MWD hand

Directional Driller:

Name of Directional hand

Witness Witness

Positive Pulse T.F.O. from PROGTM:

163.25 degrees

Gravity Tool Face (gtface) Should Equal Zero:

0.00

Motor Adjustment:

2.12 / G degrees/setting

degrees

nd

Alignment of Mule Shoe Sleeve Key to Motor Scrib e: Name of 2 MWD hand Witness O.T.F.=0, Entered into Computer by: All Calculations Witnessed by: Driller

3-6

Name of MWD hand Signature of Directional


MWD - Positive Pulse OTF – External Drill Collar Offset Magnetic Declination Toolface switch over

3-7


EM MWD Toolface Offset Magnetic Declination

The “Bearing Display” GEOGRAPHIC radio button must be selected for the Declination value to be applied (by the surface software) to the transmitted magnetic hole direction.

3-8


Toolface Offset

Zero tool face offset G4 – this is the internal of fset for the CDS probe; this value must always be entered as a NEGATIVE number fr om 0 to –360; this value is applied by the surface software. Tool face offset DC – this is the external (drill collar) offset; must be m easured clockwise (looking toward bit) from the muleshoe boltholes to the mud motor scribeline (if using a stinger). For slimhole, measure from the CSGx locking bolts to the mud motor scribeline. When using a bipod measure from the tool carrier scribeline to the m ud motor scribeline.

3-9


The main page software display can be checked to verify that the appropriate declination and toolface offset are being applied to the transmitted data.

3-10


Toolface Offset Summary

Mud Pulse System

Internal Offset

Negative Pulse

Positive Pulse

None

Directional Probe (DAS)

DAS highside is mechanically oriented to align with pulser anchor bolts

Determine offset as per procedure and PROGTM into the DAS

Surface Software

Surface Software

Measure clockwise from anchor bolts to motor

Typical: Muleshoe sleeve is aligned with motor scribeline, therefore offset = 0 °

External Offset 0 to +360 values permitted °

°

Optional : If muleshoe sleeve is not aligned with motor scribeline, calculate offset as per procedure 0 to +360 values permitted °

3-11


°

EM System

Electromagnetic Telemetry Surface Software

Internal Offset

Determine offset as per procedure and always enter value as a NEGATIVE number. (Zero toolface offset G4, “Job Data” screen) 0 to -360 values permitted °

°

Surface Software Bipod : Measure clock wise from the tool carrier key to the mud motor scribeline. 0 to +360 values permitted. °

External Offset

°

S tinger : Measure clockwise from muleshoe boltholes to mud motor scibeline. 0 to +360 values permitted. °

°

Slimhole: With CSGx module, measure clockwise from the CSGx locking bolt to mud motor scribeline. 0 to +360 values permitted. °

3-12


°

Precision LWDTM Tool Face Offset The Tool Face Offset is an external (drill collar) offset and must be measured clockwise, looking downward toward the bit from the HEL tool scribeline to the mud motor scribeline. This is one of the most important measurements that the LWD Engineer makes and MUST be done correctly. All other work and activity performed by the LWD Engineer means naught if the well must be plugged back with cement because of an incorrect TFO calculation (or the correct TFO not being entered into the Spectrum software). Ensure that the TFO calculation is correct, entered into Spectrum correctly and verified by the Directional Driller. The procedure for measuring the TFO is as follows: 1. Measure in a clockwise direction the distance from the HEL tool’s high side scribe to the motor high side scribe. Record this length into the TFO work sheet as the TFO distance. In the following example, this value is 351 mm. 2. Measure the circumference of the tubular at the same location where the TFO distance is being measured. Record this length into the TFO work sheet as the Circumference of Collar. 3. Calculate the TFO angle using the following formula:

TFO Angle

=

TFO Dis tan ce Collar Circumference

∗

360

From the above example, if the collar circumference is 500 mm,

TFO Angle

=

351 500

∗

360

=

0.702 ∗ 360

=

252.72o

A sample form is as follows:

Computalog USA, Inc. This document contains Company proprietary information which is the confidential property of Computalog Drilling Services and shall not be copied, reproduced, disclosed to others, or used in whole or in part for any other purpose or reason except for the one it was issued without written permission.

Computalog USA, Inc. This document contains Company proprietary information which is the confidential property of Computalog Drilling Services and shall not be copied, reproduced, disclosed to others, or used in whole or in part for any other purpose or reason except for the one it was issued without written permission.

Computalog Drilling Services

Directional Sensors

Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without the expressed written consent of Computalog. Survey intro.doc

date

4-1

Doc. # TD2007.rev A


INTRODUCTION The Directional Sensor is made up of electronic printed circuit boards, a Tensor Tri-Axial Magnetometer and a Tensor Tri-Axial Accelerometers, and Temperature sensor. These modules are configured into a directional probe and are run in the field mounted in a nonmagnetic drill collar. The Directional Sensor provides measurements, which are used to determine the orientation of the drill string at the location of the sensor assembly. The Directional Sensor measures three orthogonal axis of magnetic bearing, three orthogonal axes of inclination and instrument temperature.

These measurements are

processed and transmitted by the pulser to the surface. The surface computer then uses this data to calculate parameters such as inclination, azimuth, high-side toolface, and magnetic toolface. The sensor axes are not perfectly orthogonal and are not perfectly aligned, therefore, compensation of the measured values for known misalignments are required in order to provide perfectly orthogonal values. The exact electronic sensitivity, scale factor and bias, for each sensor axis is uniquely a function of the local sensor temperature. Therefore, the raw sensor outputs must be adjusted for thermal effects on bias and scale factor. Orthogonal misalignment angles are used with the thermally compensated bias and scale factors to determine the compensated sensor values required for computation of precise directional parameters.


date

4-2

Doc. # TD2007.rev A


DIRECTIONAL SENSOR HARDWARE The figure above shows the basic configuration of the Directional Sensor probe. The directional probe is mounted to the MWD assembly and keyed into a Non-Magnetic Drill Collar. The nominal length of the sub is 30 feet. The nonmagnetic collar is usually referred to as Monel.

DIRECTIONAL SENSOR COMPONENTS Contained inside the assembly is a Single Port MPU, Triple Power Supply and a Digital Orientation Module. The Single Port MPU is a modular micro-controller assembly based on the Motorola MC68HCll microprocessor implementing Honeywell's qMIXTM communications protocol (qMIX/ll TM). The Triple Power Supply provides regulated power for the complete assembly. The microprocessor provides the control and timing to interface the logic circuit controls the analog power switch. With the analog power switch off only the 5 volt circuits are active and the current drain from the sub bus is approximately 8 milliamps. When the logic board switches on the analog power switch, battery power is directed to the 12 volt regulator on the analog circuit. The current drain with the analog power switch on and the sensors off is approximately 80 milliamps. With the accelerometers powered up the current drain is approximately 120 milliamps. With the magnetometer powered up the current drain is approximately 140 milliamps.


date

4-3

Doc. # TD2007.rev A


ANALOG Circuit The Analog Circuit provides an interface with the inclinometer, magnetometer, and pressure transducer sensors. The 16 channel multiplexer on the analog circuit takes input from various sensor outputs and sends the data to the logic circuit for transmission. A sensor power switch takes power from the 12 volt regulator and selectively powers up the accelerometers and magnetometers. A 5 volt excitation supply from the 12 volt regulator is used to power the pressure transducer. The status voltages appear on the surface probe test and are defined as follows: 1. Sub Bus Voltage - battery voltage on the sub bus. 2. 5 Volt Supply - the 5 volt excitation supply from the 12 volt regulator that

powers the pressure transducer. 3. Accelerometer Power Status - voltage that is currently being supplied to the

inclinometer

(0 or 12.5v).

4. Magnetometer power Status - voltage that is currently being supplied to the

magnetometer (0 or

12.5v).

5. Steering Mode Status - 4.5 volts when steering mode is set.

TENSOR INCLINOMETER The TENSOR Tri-axial Accelerometer measures three orthogonal axes of inclination (Gx, Gy, and Gz) and also includes a temperature sensor. The inclinometer has a 1g full scale output in survey mode and a 7 g full scale output in steering mode. The sensor operates within the following parameters: 1. Input Voltage

+/- 12.5 to 15.5 volts

2. Input Current < 80 ma/g 3. Accelerometer Output

3.0 ma/g


date

4-4

Doc. # TD2007.rev A


AC C ELER O M ETER AC CE LER AT IO N

U P PE R M A G N E T

CAP ACITAN CE PICK O FF

TOR Q UER COIL

CH EM ICA LLY M ILLED H IN G E

Q U A R T Z PR O O F M ASS

LEAD SUPPO RT PO STS

LO W ER M AG N ET

The inclinometer is made up of three accelerometers. The operation of the accelerometer is based on the movement of a quartz proof mass during acceleration. The figure above is a diagram of a accelerometer. The accelerometer consists of two magnets and a quartz disc with a coil attached to it. The quartz disc is a proof mass with a hinge that has been chemically etched to allow movement in one direction. A torquer coil is attached to the proof mass, which is suspended between the two permanent magnets. The proof mass position is maintained by applying current to the torquer coil.

The magnets have

reference plates, which measure the capacitance between the two magnets. When a force is applied to the accelerometer, movement of the proof mass changes the capacitance. A circuit detects the change in capacitance and applies current to the torquer coil to restore the proof mass to its original position. The amount of current required to restore the proof mass to its original position is a function of the amount of force applied to the accelerometer. Force is related to acceleration by F = ma. We measure the acceleration of gravity in g's (gravity units) in Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without the expressed written consent of Computalog. Survey intro.doc

date

4-5

Doc. # TD2007.rev A


three orthogonal directions relative to the Directional Sensor probe. This allows us to calculate the inclination of the tool relative to vertical. The scaling of the X and Y accelerometer channels depends on the operational mode (survey or steering), while the Z channel and the temperature sensor have the same scaling for both modes. The full scale output voltage sensitivity for each mode is as follows:

CHANNEL

SURVEY

STEERING

1. X Accelerometer

4.5 v/g

642 mv/g

2. Y Accelerometer

4.5 v/g

642 mv/g

3. Z Accelerometer

4.5 v/g

4.5 v/g

4. Temperature

10 mv/deg K

10 mv/deg K

TENSOR MAGNETOMETER The Tensor Tri-axial Magnetometer measures three orthogonal axes of magnetic bearing (Bx, By, and Bz) as well as temperature. The Tensor Model 7002MK Magnetometer has an output operating range of plus and minus 100,000 Nanotesla (the earth's field is about 50,000 Nanotesla) and operates within the se parameters:

1. Input voltage +/- 12 - 18 vdc 2. Input current 25 milliamps 3. Flux Gate Output 1 mv / 20 Nanotesla 4. Temperature Output Voltage 10 mv / oK


date

4-6

Doc. # TD2007.rev A


TE N S O R R IN G C O R E FLU X G A T E M A G N E TO M E TE R

EXTERNAL M A G N ETIC FIELD

O SC

PEAK DET

OUTPUT A M P

D R IVE R SERVO A M P

The Tensor magnetometer is a saturable core device. It consists of two coils with a

core between them, which has a certain magnetic permeability. A magnetic field produced by one coil travels through the core and induces a current in the other coil. The core will only transmit a certain amount of magnetic field, that is , when the level of magnetic flux gets to a certain point the core will become saturated and greater amounts of flux will not pass through the core. The point at which a substance becomes saturated is a property of that substance, i.e. certain metals will saturate sooner than others. The magnetometer continually drives the core to saturation. In the presence of an external magnetic field the point that the core saturates is shifted. The signal shift is detected, amplified, and fed back as a bucking magnetic field to maintain the core at a balanced around zero magnetizing force. The servo amplifier offset caused by the signal shift is further amplified and presented as the output of the magnetometer. In the tri-axial set of magnetometers, the three flux gate channels and temperature channel are supplied power conditioned by a common pair of internal regulators. The individual magnetometer transducers come in biaxial sets. The magnetometer Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without the expressed written consent of Computalog. Survey intro.doc

date

4-7

Doc. # TD2007.rev A


package contains two biaxial magnetometers, of which only three axes are used. The sub bus around the magnetometer requires particular attention because the current through the sub bus is alternating current, any change in that current will produce a magnetic field that can affect the magnetometer.

DIRECTIONAL SENSOR MEASUREMENTS AND CALCULATION The measurements that we make with the DIRECTIONAL SENSOR are made relative to these axes. The X-axis is perpendicular to the tools long axis and is in the direction of the scribe line etched on the DIRECTIONAL SENSOR nonmag sub. The Y-axis is also perpendicular to the long axis. The Z-axis is along the long axis of the DIRECTIONAL SENSOR; in the direction the hole is being drilled. The scribe line on the DIRECTIONAL SENSOR sub allows measurement of the relationship between the tools axis and the bent sub or mud motor scribe line. This measurement is called the toolface offset. The toolface offset is measured by extending the bent sub scribe line to the DIRECTIONAL SENSOR scribe line and measuring the degrees offset with a compass. The measurement is made from _________ scribe line to _____________ scribe line using the right hand rule, thumb pointing in the direction of the hole, measure in the direction the fingers of your right hand are pointing. Running a highside orientation program in the MWD software can also make the measurement.

TO O L PH YS IC A L A XIS

X

scribe line

Y

Z


date

4-8

Doc. # TD2007.rev A


The main parameters that we calculate with the raw data from the DIRECTIONAL SENSOR are as follows: Highside Toolface is the angle between the deflection tool scribe line and the top or

highside of the hole. This is calculated using the X-axis and Y-axis inclinometer measurements. Magnetic Toolface is the direction that the deflection tool scribe line is pointing relative

to true or grid north. This is calculated using the X-axis and Y-axis magnetometer measurements.


date

4-9

Doc. # TD2007.rev A


Inclination is the angle between vertical and the wellbore in the vertical plane. We

measure this angle by measuring the direction that gravity acts relative to the tool. Gravity acts in a vertical direction and has a magnitude of 1 g at sea level at the equator. Azimuth is the direction of the wellbore relative to true or grid north in the horizontal

plane. We measure this angle by measuring the direction of the earth's magnetic field relative to the tool. Magnetic Declination is the difference in degrees between magnetic north and true north

or grid north for a particular location on the earth. This value changes with time and location and must be determined using the software program. On a directional well it is important that the value for magnetic declination that we use is the same one that the directional driller is using. Usually there will be a difference between the value that the software calculates and the one that the directional driller provides, however, always use the value provided by the directional driller. Magnetic Field Strength is the total magnitude of the earth's magnetic field in Nanotesla

for a particular location on the earth. This value also changes

with

time

and

location

and

can

be

determined

using

the

software program. Magnetic Dip Angle is the

angle between horizontal and the earth's magnetic field force lines. This angle increases as you go north toward the magnetic north pole. If you were exactly on top of the magnetic north pole the angle would be 90 degrees.


date

4-10

Doc. # TD2007.rev A


HIGHSIDE TOOLFACE The X-axis and Y-axis inclinometer measurements are required to calculate highside toolface. The figure below is a vector diagram showing the highside toolface measurement. On the left is a diagram of the tool and its relationship to the X - Y plane and the gravity vector, along with the components of gravity in the X - Y plane and on the Z-axis. Gxy is the vector sum of the X and Y components of the gravity vector

measured by the tool. On the right is a diagram of the X - Y plane showing the X and Y components of the gravity vector and the sum Gxy. Highside toolface is the angle between the X axis and the highside of the hole and is calculated as follows: Gxy = ( Gx2 + Gy2)1/2 COS ( HSTF) = -Gx / Gxy SIN (HSTF) = Gy / Gxy HSTF = ATAN ( Gy / -Gx ) or

Where:

HSTF = ATAN2 ( Gy, -Gx)

Gx = Gravity vector in the X direction Gy = Gravity vector in the Y direction Gxy = Sum of the X and Y vectors HSTF = Highside toolface and all vectors are in gravity units.


date

4-11

Doc. # TD2007.rev A


MAGNETIC TOOLFACE The X-axis and Y-axis magnetometer measurements are required to calculate magnetic toolface. Bxy is the vector sum of the X and Y components of the magnetic vector measured by the tool. Magnetic toolface is the direction the scribeline is pointing and is calculated as follows: Bxy = ( Bx2 + By2)1/2 MTF = ATAN ( By / -Bx )

Where:

or

MTF = ATAN2 ( By, -Bx)

Bx = Magnetic vector in the X direction By = Magnetic vector in the Y direction Bxy = Sum of the X and Y vectors MTF = Magnetic toolface and all vectors are in gravity units.


date

4-12

Doc. # TD2007.rev A


INCLINATION

To calculate inclination we use the X, Y, and Z inclinometer measurements. The figure shows a diagram of the tool and the relevant axes. Again, Gxy is the sum of the X and Y components of the gravity vector as calculated above. Gz is the Z component of the gravity vector as measured by the tool. Gtotal is the total gravity vector and is the sum of the X, Y, and Z components. This sum should be equal to 1 g, as long as your elevation is relatively close to sea level. Inclination is the angle between the Z axis and vertical and is calculated as follows: Gtotal = ( Gxy2 + Gz2 )1/2 Sin ( INC ) = Gxy / Gtotal

or

INC = ASin Gxy

Cos ( INC) = Gz / Gtotal

or

INC = ACos Gz

INC = ATAN ( Gxy / Gz ) INC = ATAN2 (Sin (HSTF) Gy – Cos (HSTF) Gx, Gz) Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without the expressed written consent of Computalog. Survey intro.doc

date

4-13

Doc. # TD2007.rev A


Where:

Gxy = the sum of X and Y gravity components Gz = the Z axis gravity component Gtotal = the sum of the X, Y, and Z gravity components INC = inclination units are in g's.

Note that since we know that Gtotal is 1 g, we can calculate inclination from only the X and Y measurements, or only the Z measurement if one of the accelerometers fail, however, if only Gz is known the accuracy at low angles is less because the Z accelerometer is near full scale.

For Gz only: Not accurate for inclination less than 15o +/- 1/2o accuracy for inclination greater than 15 o and less than 30o +/- 1/4o accuracy for inclination greater than 30 o and less than 45o +/- 1/8o accuracy for inclination greater than 45 o

LONG COLLAR AZIMUTH To calculate azimuth using the conventional method the following data is required:

1. Bx = magnetic field vector in the X direction 2. By = magnetic vector in the Y direction 3. Bz = magnetic vector in the Z direction 4. HSTF = highside toolface 5. INC = inclination Azimuth is referenced in the horizontal plane to true or grid north. The magnetic field that we measure, however, is at some angle from the horizontal, that is the magnetic dip angle. Therefore to reference our measurement to true north in the horizontal plane we Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without the expressed written consent of Computalog. Survey intro.doc

date

4-14

Doc. # TD2007.rev A


must project the magnetic vector to the horizontal. This is why you need HSTF and inclination to calculate azimuth.

Where:

Bn = horizontal component of the magnetic vector Btotal = total magnetic field strength DIP = magnetic dip angle

Combining the above equations for raw azimuth yields the following:

Bx Sin (HSTF) + By Cos (HSTF) AZ = ATAN {--------------------------------------------------------------------------} (Bx Cos (HSTF) - By Sin (HSTF)) Cos (Inc) + Bz Sin (Inc)


date

4-15

Doc. # TD2007.rev A


SHORT COLLAR AZIMUTH Traditional compass type surveying instruments with their ability to sense only the direction of the local magnetic field vector must be used in conjunction with enough nonmagnetic drill collars so that the local magnetic field vector is

uncorrupted by drill string magnetization. With solid state magnetometers and their ability to measure 3 orthogonal axes of the local magnetic vector it is possible to compensate for axial magnetization and use much shorter lengths of nonmagnetic material. Azimuth is defined as any azimuth measurement made with respect to the local magnetic field without correction, ie. the long collar azimuth. When there is no magnetic interference the azimuth is the true azimuth, otherwise an extraneous magnetic field produces a systematic error in the azimuth measurement and the long collar azimuth differs from the true azimuth. The short collar azimuth is based upon a patented technique that uses the magnitudes of the magnetic field components Bx and By in conjunction with the known values of the earth's magnetic field strength and dip angle to compensate for the corrupted Bz measurement. An instrument used with the corrected azimuth technique requires highly accurate calibration, because the absolute magnitudes of the field vector components are required. The long collar azimuth, however, requires only ratios of the magnitudes of these components, thus reducing the calibration complexity and scale factor errors for this measurement.

SURVEY QUALITY The following items will be used to validate a MWD survey: 2

2

2

Gtotal = (Gx + Gy +Gz ) ½ G total - this value is equal to (G x2 + Gy2 + Gz2)1/2, and should be within

+0.003 g of the local gravity, which is 1.000 g in most locations. A G total value outside of these limits may indicate that the Directional Sensor did not achieve stability during accelerometer polling, there was a hardware failure, BHA movement or improper misalignment and/or scale/bias values were used.


date

4-16

Doc. # TD2007.rev A

Computalog Drilling Services 2

2

2

Btotal = (Bx + By +Bz ) ½ B total is equal to (Bx2 + By2 + Bz2)1/2, and should trend consistently over the interval

of a bit run. Under ideal conditions, i.e., no cross-axial or axial magnetic interference, Btotal should read the earth's local magnetic field strength. Abrupt variations in Btotal during a bit run will be caused by a "fish", a nearby cased well bore, certain mineral deposits, solar events, localized magnetic anomalies, or a hardware failure. Since all of the above will typically affect all three magnetometer responses, magnetic interference will be detectable by tracking the B total value. As a general guideline, B total should not vary by more than +- 350 Nanotesla from the local magnetic field strength or from survey to survey during a bit run. The local magnetic field strength is determined by using magnetic modeling software or directly measuring it through infield referencing. Surveys which do not conform to this guideline should alert the field engineer that some magnetic interference is probable or that there was a hardware failure. Btotal may also change abruptly from bit run to bit run due to a change in BHA configuration, which does not have the correct Monel spacing. Magnetic Dip Angle should trend consistently over the interval of a bit run.

Under ideal conditions, (i.e., no cross-axial or axial magnetic interference or pipe movement), MDIP should read the earth's local magnetic dip angle. Abrupt variations in MDIP during a bit run will be caused by a "fish", a nearby cased well bore, certain mineral deposits, solar events, localized magnetic anomalies, pipe movement or a hardware failure. (Bx * Gx) + (By * Gy) + (Bz * Gz) MDIP = ASIN {-------------------------------------------------------} Gtotal * Btotal

As a general guideline, MDIP should not vary by more than +- 0.3 degrees from the local magnetic dip angle or from survey to survey during a bit run. The local magnetic dip angle is determined by using magnetic modeling software or directly measuring it through infield referencing. Surveys which do not conform to this guideline should alert the field engineer that some magnetic interference or pipe movement is probable, or that there was a hardware failure. MDIP may also Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without the expressed written consent of Computalog. Survey intro.doc

date

4-17

Doc. # TD2007.rev A


change abruptly from bit run to bit run due to a change in BHA configuration, which does not have the correct Monel spacing.

MAGNETIC INTERFERENCE Magnetic interference problems when surveying a well are usually due to casing or a fish that has been left in the hole. Unfortunately, the majority of the magnetic interference problems occur when the accuracy of our azimuth is very critical. A well is usually kicked off just below a casing shoe or through a window in the casing. The casing is a large concentration of magnetic material, the ends of which act like magnetic poles from which the curving flux lines cause magnetic interference. On production platforms or pads nearby wells can cause interference as well. The magnetic interference that we are primarily concerned with is in the X and Y direction. This is due to the fact that magnetic toolface uses the X and Y magnetometers to calculate toolface. Also with the Short collar method of surveying, only the X and Y magnetometers are used. A good way of determining how much magnetic interference we are getting on the Z-axis with the Short collar method is to compare Btotal measured with Btotal calculated. The X and Y magnetometers will react to magnetic interference in the same manner as the Z magnetometer. This would mean that a perpendicular distance of about 30' would be required when kicking off near casing. The orientation of the casing with respect to the magnetometers may have some effect on how much azimuth is affected. As the tool is rotated, X and Y interference changes, but Btotal should stay the same.


date

4-18

Doc. # TD2007.rev A


Non-Mag Spacing

When kicking off a well below casing, it is necessary to have at least 10 diameters of clearance between the shoe and the DIRECTIONAL SENSOR. When kicking off next to another well or a fish, where the magnetic interference is perpendicular to the tool, up to 30' clearance may be required to obtain good magnetic toolface or surveys. Take special care when running a magnetic survey to prevent the effects of magnetic interference. Such interference can be caused by proximity to steel collars and by adjacent casing, hot spots in nonmagnetic collars, magnetic storms, and formation with diagenetic minerals.

Nonmagnetic drill

collars

are

used

to

separate

the

electronic

survey

instrumentation from the magnetic fields of Drill string both above and below and prevent the distortion of the earth's magnetic field at the sensor. The collars are of four basic compositions: (I) K Monel 500, an alloy containing 30% copper and 65% nickel, (2) chrome/nickel steels (approximately 18% chrome, 13% nickel), (3) austenitic steels based on chromium and manganese (over 18% manganese) and (4) copper beryllium bronzes. Currently, austenitic steels are used to make most nonmagnetic drill collars. The disadvantage of the austenitic steel is its susceptibility to stress corrosion in a salt mud environment. The K Monel and copper beryllium steels are to expensive for most drilling operations; both however are considerably more resistant to mud Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced electronically or used for any purpose without the expressed written consent of Computalog. Survey intro.doc

date

4-19

Doc. # TD2007.rev A


correction than austenitic steels. The chrome/nickel steel tends to gall, causing premature damage to the threads. When the electronic survey instrumentation is located in a nonmagnetic collar between the bit and steel collars the distortion of the earths magnetic field is minimized and it is isolated from drill string interference generate both above and below the electronic survey instrumentation unit. The number of required nonmagnetic collars depends on the location of the well bore on the earth and inclination and direction of the well bore. The figure above is a compilation of empirical data that are fairly reliable in selecting the number of nonmagnetic drill collars. First, a zone is picked where the well bore is located either zone 1, 2 or 3. Then the expected inclination and direction are used locate the curve, either A, B or C. Example, on the north slope of Alaska a well plan calls for an inclination of 60 degrees and a magnetic north azimuth of 50 degrees. Solution, The north slope of Alaska is in zone 3. From the chart for zone 3 at 60 degrees inclination and 50 degrees magnetic north azimuth, the point falls in Area B, indicating the need for two 30’ magnetic collars with the electronic survey instrumentation unit 8 -10 feet below the center. This is just a recommendation and the survey should always be checked to make sure it is with in acceptable tolerances of the (non-corrupted) earth's magnetic field.


date

4-20

Doc. # TD2007.rev A


Empirical Data Charts for Nonmagnetic Drill Collar Spacing

ZONE 1

ZONE 2

ZONE 3

90

90

90

80

80

80

70

70

70

60

60

60

50

50

50

40

40

40

30

30

30

20

20

20

10

10

10

10 20 30 40 50 60 70 80 90

10 20 30 40 50 60 70 80 90

10 20 30 40 50 60 70 80 90

Direction Angle from Magnetic N or S



Compass Spacing

Compass Spacing

Compass Spacing

Area A 18’ collar: 1’ to 2’ below center Area B 30’ collar: 3’ to 4’ below center Area C tandem 18’+25’: center of bottom collar

Area A 30’ collar: 3’ to 4’ below center Area B 60’ collar: at center Area C 90’ collar: at center

Area A 60’ collar: at center Area B 60’ collar: 8’ to 10’ below center Area C 90’ collar: at center


date

4-21

Doc. # TD2007.rev A


SURVEY ACCURACY Survey accuracy is a function of both instrument related uncertainties and systematic uncertainties. Instrument related uncertainties include such things as sensor performance, calibration tolerances, digitizer accuracy, and resolution. This is defined as the baseline uncertainty and it is present in all survey sensors. Systematic uncertainties are a function of magnetic interference from the drill string and can be reduced by housing the instrument in a longer nonmagnetic drill collar. The total uncertainty is equal to the baseline uncertainty plus the systematic uncertainty. The long collar azimuth, when measured in an environment free from magnetic interference, will always provide the most accurate azimuth, the only uncertainty being the baseline uncertainty. The Short collar algorithm corrects for systematic uncertainties due to the presence of magnetic interference along the Z axis of the magnetometer. For the Short collar method, the systematic uncertainty is in the values that we obtain for the magnetic field strength and dip angle. Due to the fact that this uncertainty is along the Z axis, survey accuracy will be a function of inclination and azimuth, as well as dip angle and magnetic field strength. If we consider only the baseline uncertainty, in the absence of magnetic interference, survey accuracy will be a function of inclination and magnetic dip angle. This relationship is shown in figures below, where Bn (Bnorth) is defined as the projection of the magnetic field vector in the horizontal plane, Berror is defined as the baseline uncertainty and has a constant value, and Bref is defined as the measured measured magnetic magnetic field field vector (Bref = Bn + Berror). As shown in the figure below, as the inclination increases, the horizontal projection of Berror is a larger percentage of Bref resulting in a decrease in survey accuracy. In the figure below, the effect of magnetic dip angle on survey accuracy is shown. As the magnetic dip angle increases, the size of the horizontal

Confidential and Proprietary information of Computalog USA and Computalog LTD. This material is not to be reprinted, reproduced reproduced electronically or used for any purpose without the expressed written consent of Computalog. Survey intro.doc

date

4-22

Doc. # TD2007.rev A


S U R V E Y A C C U R A C Y A S A F U N C T IO N O F IN C LIN A TIO N

B ref @ IN C 2

B err erro r

B ref @ IN C 1 N O R T H

B n2 IN C 1 B error IS A LA R G E R P E R C E N T A G E O F B re ref A T H IG H E R IN C LIN A TIO N S

IN C 2

B n1

V E R T IC A L

projection of Bn decreases, resulting in a larger percentage of Berror in Bref. Thus anything that causes the horizontal projection of Berror to increase or Bn to decrease results in a decreased survey accuracy.

For systematic uncertainty, the uncertainty is along the Z-axis. This will result in decreased survey accuracy when drilling east or west as opposed to drilling north or south. This is due to the fact that Berror will tend to pull Bref in the direction of the Zaxis, away from Bn. This relationship is shown in the figure below.


date

4-23

Doc. # TD2007.rev A


SUR VEY ACC UR AC Y AS A FUNC TIO N O F M A G N ETIC D IP

CONSTANT B error

B ref B ref N O R TH

A S M A G D IP IN C R EA SE S B error IS A LA R G ER PE R C EN TA G E O F B ref

Bn Bn

IN C R EA SIN G M A G D IP VE R TIC A L

E F F E C T D R IL L IN G E A S T O R W E S T O N S U R VE Y A C C U R A C Y

N O R T H

B re f = B n + B e rr rro r B n

A Z IM U T H

Z A X IS

E R R O R IN A Z IM U T H B e rr rro r EAST


date

4-24

Doc. # TD2007.rev A


DIRECTIONAL SENSOR CALIBRATION The accuracy of borehole azimuth and inclination measurements are largely dependent on our ability to identify and correct constituent errors in the individual sensors that are used to calculate the directional parameters of the well bore. These sensors include the three orthogonal accelerometers and three orthogonal magnetometers. The calibration process is based upon the known value of the total field intensity of both the gravity and magnetic fields at the location of the calibration. Each sensor is rotated through the known field and its output is compared with known values. This process yields a set of values for bias, scale factor, and alignment corrections over a range of temperatures from room temperature to the upper operating limit. The data is fit to a third order polynomial so that the correction factors can be applied at any given temperature within the operating range of the tool. To be certain that the a calibration technique will meet the performance as well as maintenance objectives it must meet the following objectives:

1. Total package evaluation 2. Repeatability 3. Tolerant of positioning errors during calibration 4. Reliability under down hole conditions The calibration is performed at the highest level of assembly through the instruments data acquisition system and final housing. This allows a total package model to be built so that errors do not accumulate as separate modules are incorporated into each other. Repeatability and tolerance to positioning errors during calibration is achieved by establishing specific performance standards for each sensor and through the methodology of the calibration itself. Reliability under down hole conditions is addressed at the Materials Testing Laboratory by exposing each sensor to vibration and thermal cycling while monitoring their output. Reliability is also achieved through failure analysis and design and modification of the sensor package.


date

4-25

Doc. # TD2007.rev A


CALIBRATION METHODOLOGY The calibration procedure consists of rotating the sensor through the field of investigation for each axis and comparing the output with known values. Examine the ideal response of a single axis rotation, at 0 degrees the sensor axis is aligned with the field and the output voltage is at a maximum. As you rotate the sensor counter clockwise the voltage decreases until at 90 degrees the output goes to 0 volts. As you continue to rotate the sensor counter clockwise the output voltage goes negative above 90 degrees and reaches a maximum negative value at 180 degrees. The response as you go from 180 to 360 degrees is similar. Note that this response applies to both accelerometers and magnetometers when rotated through the gravity or magnetic field. Scale factor corrections scale the output of the sensor to a given standard so that all sensors will have the same voltage response to a given field. Alignment errors are positioning errors between the individual transducers and the DIRECTIONAL SENSOR probe true physical axis. The computation of bias, scale factor, and alignment corrections based on the examination of a single axis would put considerable accuracy requirements upon both the calibration fixtures and the personnel that operate operate them. By performing an analysis using data simultaneously obtained from multiple axes greatly reduces sensitivity to positioning errors and improves repeatability.


date

4-26

Doc. # TD2007.rev A


REFERENCES 1.

Estes, R. A., and

Walters, P. A.,

"Improvement of MWD Azimuth

Accuracy by use of Iterative Total Field Calibration Technique Technique and Compensation for System Environmental Effects", SPE paper presented at the 1986 MWD Seminar, May 16. 2.

Russell, A. W., and Roesler, R. F., "Reduction of Nonmagnetic Drill Collar

Length Through Magnetic Magnetic Azimuth Correction Technique" , paper SPE / IADC IADC 13476 presented at at the 1985 Drilling Drilling Conference, New Orleans Orleans


date

4-27

Doc. # TD2007.rev A


Goxy = (gx2 + gy2) 1/2

Boxy =(bx2 + by2) 1/2

Gtotal = (gx2 + gy2 +gz2 ) 1/2

Btotal = (bx2 + by2 +bz2 ) 1/2

HSTF = ATAN (Gy / -Gx) this does not correct for quadrant

HSTF = ATAN2 ( Gy, -Gx) this does correct for quadrant

MTF = ATAN (By/ -Bx) this does not correct for quadrant

MTF = ATAN2 (By, -Bx) this does correct for quadrant o

INC = ATAN (Goxy / Gz) this does not work above 90

o

INC = ATAN2 (Sin (HSTF) Gy – Cos (HSTF) Gx, Gz) this works above 90

INC = ASIN (Goxy)

INC = ACOS (Gz)

Bx Sin (HSTF) + By Cos (HSTF) AZ = ATAN {--------------------------------------------------------------------------} (Bx Cos (HSTF) - By Sin (HSTF)) Cos (Inc) + Bz Sin (Inc)

(Bx * Gx) + (By * Gy) + (Bz * Gz) MDIP = ASIN {-------------------------------------------------------} Gtotal * Btotal


Take special care when running a magnetic survey to prevent the effects of magnetic interference. Such interference can be caused by proximity to steel collars and by adjacent casing, hot spots in nonmagnetic collars, magnetic storms, and formation with diagenetic minerals. Nonmagnetic drill collars are used to separate the electronic survey instrumentation from the magnetic fields of Drillstring both above and below and prevent the distortion of the earth’s magnetic field at the sensor. The collars are of four basic compositions: (1) K Monel 500, an alloy containing 30% copper and 65% nickel, (2) chrome/nickel steels (approximately 18% chrome, 13 % nickel), (3) austenitic steels based on chromium and manganese (over 18% manganese) and (4) copper beryllium bronzes. Currently, austenitic steels are used to make most nonmagnetic drill collars. The disadvantage of the austenitic steel is its susceptibility to stress corrosion in a salt mud environment. The K Monel and copper beryllium steels are to expensive for most drilling operations; both however are considerably more resistant to mud corrosion than austenitic steels. The chrome/nickel steel tends to gall, causing premature damage to the threads. When the electronic survey instrumentation is located in a nonmagnetic collar between the bit and steel collars the distortion of the earths magnetic field is minimized and it is isolated from drill string interference generate both above and below the electronic survey instrumentation unit. The number of required nonmagnetic collars depends on the location of the wellbore on the earth and inclination and direction of the wellbore. The figure above is a compilation of empirical data that are fairly reliable in selecting the number of nonmagnetic drill collars. First, a zone is picked where the wellbore is located either zone I, II or III. Then the expected inclination and direction are used locate the curve, either A, B or C. Example , on the north slope of Alaska a well plan calls for an inclination of 55 degrees and an azimuth of 40 degrees. Solution, The north slope of Alaska is in zone III. From the chart for zone III at 55 degrees inclination and 40 degrees azimuth, the point fall just below curve B, indicating the need for two magnetic collars with the electronic survey instrumentation unit 8 – 10 feet below the center. This is just a recommendation and the survey should always be checked to make sure it is with in acceptable tolerances of the (non-corrupted) earth’s magnetic field. Tolerances Total Magnetic Field +/- 0.003 gauss Magnetic Dip Angle +/1 .15 degrees Reference

Bourgoyne, Millhelm, Chenevert, Young: “Applied Drilling Engineering” SPE textbook series, vol. 2, 1991.

Basic Math Concepts Module Objectives

Basic Math Concepts Directional drillers require a knowledge of basic math concepts, including a minimum competence in algebra, geometry, and trigonometry. You generally perform any calculations required at the rigsi te using a computer or programmable calculator, but it is useful to check them by hand.

Module Objectives Solve simple trigonometric equations. Understand basic trigonometric functions.

Geometry The directional driller may be asked to perform calculati ons involving angles, right triangles, and similar triangles.

6-1

Basic Math Concepts Geometry

Right Triangles A right triangle is one in which one of the angles equals 90 o. Consequently, the sum of the other two angles is also 90o. In the illustration below, if b = 28o15’, find angle a.

c = 90°

a

b = 28° 15’

c

b

Figure 1 Finding missing angles in a right triangle

c = 90o b + a = 90o a = 90o - 28o15’ a = 61o45’

6-2

Basic Math Concepts Trigonometry

Trigonometry The directional driller may be asked to solve simple trigonometric equations. In a right triangle, such as the one shown below, the side opposite to the right angle (side C ) is called the hypotenuse.

a C B

c = 90°

b A

Figure 2 Relationship of angles to sides in a right triangle

6-3


Sines, Cosines, Tangents, and Cotangents The following trigonometric functions are defined:

) t n e c a j d A ( B

a C ( H y p o t e n u s e )

c = 90°

b A (Opposite)

Figure 3 Trigonometric functions for angle a

Opposite A sin a = ------------------------------- = --- Hypotenuse C

Adjacent B cos a = ------------------------------- = --- Hypote nuse C

Opposite A tan a = ------------------------ = -- Adja cen t B

6-4


a C B

c = 90°

b A

Figure 4 Relationships among complementary angles in a right triangle

A sin a = ---C

B cos a = ---C

B sin b = ---C

A cos b = ---C

Therefore, sin a = cos b and cos a = sin b. In a right triangle, the sum of the two complementary angles is 90 o. The sine of one complementary angle is the same as the cosine of its complement. The cosine of one complementary angle is the same as the sine of its complement. If the complementary angle of a right triangle are 60 o and 30o, then: sin 60o = cos 30o = 0.866025 cos 60o = sin 30o = 0.5

The components of a right triangle are three sides and two angles (the third angle is 90o). Knowing the value of two components, you c an solve for the other components.

6-5


a = 60°

C = ?

0 3 = B

c = 90°

b A = ?

Figure 5 Solving for components in a right triangle

Given B = 30 and a = 60o: B cos a = ---C

B C = ----------cos a

30 C = -------------cos 60

30 cos 60 = 0.50 Therefore, C = ---------- = 60 0.50 A sin a = ---C A = C × sin a A = 60 × sin 60

sin 60 = 0.866025 A = 51.96

6-6


Derivations of Sine Opposite sin a = ------------------------------ Hypotenuse Using the equation for sine, we can use algebra to find for any of the variables. Use the Sine equation to find the Hypotenuse: Opposite sin a = ------------------------------ Hy po te nu se

Multiply both sides by the Hypotenuse

Opposite sin a × Hypotenuse = ------------------------------ Hy po te nu se

× Hypotenuse

Cancel the Hypotenuse.

sin a × Hypotenuse = Opposite

Divide both sides by sin a.

sin a × Hypotenuse Opposite ------------------------------------------------ = -----------------------sin a sin a

Cancel the sin a.

Opposite Hy po ten us e = -----------------------sin a

Finally, we get an equation to find the Hypotenuse.

Use the Sine equation to find the Opposite: Opposite sin a = ------------------------------ Hy po te nu se


Opposite sin a × Hypotenuse = ------------------------------ Hy po te nu se

× Hypotenuse

sin a × Hypotenuse = Opposite Opposite = sin a × Hypotenuse


Switch the equation. Finally, we get an equation to find the Opposite.

Use the Sine equation to find the Angle: Opposite sin a = ------------------------------ Hy po te nu se

Multiply both sides by the inverse of sin (asin). 1 Note: The inverse of Sine (asin) is the same as ------sin

Opposite asin sin a = asin ------------------------------ Hy po ten us e

Cancel the sin and asin.

Opposite a = asin ------------------------------ Hy po ten us e

Finally, we get an equation to find the Angle.

6-7


Derivations of Cosine Adjacent cos a = ------------------------------ Hypote nuse Using the equation for cosine, we can use algebra to find for any of the variables. Use the Cosine equation to find the Hypotenuse: Adjacent cos a = ------------------------------ Hy po te nu se


Adjacent cos a × Hypotenuse = ------------------------------ Hy po te nu se

× Hypotenuse


cos a × Hypotenuse = Adjacent

Divide both sides by cos a.

cos a × Hypotenuse Adjacent ------------------------------------------------- = ----------------------cos a cos a

Cancel the cos a.

Adjacent Hy po te nu se = ----------------------cos a

Finally, we get an equation to find the Hypotenuse.

Use the Cosine equation to find the Adjacent: Adjacent cos a = ------------------------------ Hy po ten us e


Adjacent cos a × Hypotenuse = ------------------------------ Hy po ten us e

cos a × Hypotenuse = Adjacent

× Hypotenuse


Switch the equation.

Ad ja ce nt = cos a × Hypotenuse Finally, we get an equation to find the Adjacent.

Use the Cosine equation to find the Angle: Adjacent cos a = ------------------------------ Hy po te nu se

Multiply both sides by the inverse of cos (acos).

Adjacent acos cos a = acos ------------------------------ Hy po te nu se

Cancel the cos and acos.

Adjacent a = acos ------------------------------ Hy po te nu se


6-8


Derivations of Tangent Opposite tan a = ----------------------- Adja cen t Using the equation for Tangent, we can use al gebra to find for any of the variables. Use the Tangent equation to find the Adjacent: Opposite tan a = ----------------------- Ad ja ce nt

Multiply both sides by the Adjacent.

Opposite tan a × Adjacent = ------------------------ × Adjacent Cancel the Adjacent. Ad ja ce nt

tan a × Adjacent = Opposite

Divide both sides by tan a.

tan a × Adjacent Opposite ----------------------------------------- = -----------------------tan a tan a

Cancel the tan a.

Opposite Ad ja ce nt = -----------------------tan a

Finally, we get an equation to find the Adjacent.

Use the Tangent equation to find the Opposite: Opposite tan a = ----------------------- Ad ja ce nt

Multiply both sides by the Adjacent

Opposite tan a × Adjacent = ------------------------ × Adjacent Ad ja ce nt

tan a × Adjacent = Opposite

Cancel the Adjacent.

Switch the equation.

Opposite = tan a × Adjacent

Finally, we get an equation to find the Opposite.

Use the Tangent equation to find the Angle: Opposite tan a = ----------------------- Ad ja ce nt

Multiply both sides by the inverse of tan (ata n).

Opposite atan tan a = atan ----------------------- Ad ja ce nt

Cancel the tan and atan.

Opposite a = atan ----------------------- Ad jac en t


6-9


Summary of Derivations of Sine, Cosine, and Tangent



c = 90°

b A (Opposite)


Opposite sin a = ------------------------------ Hypotenuse

Adjacent cos a = ------------------------------ Hypotenuse

Opposite Hy po ten us e = -----------------------sin a

Adjacent Hypotenuse = ----------------------cos a

Opposite = sin a × Hypotenuse

Adjacent = cos a × Hypotenuse

Opposite a = asin ------------------------------ Hy po ten us e

Adjacent a = acos ------------------------------ Hy po te nu se

Opposite tan a = ----------------------- Adjacen t Opposite Ad ja ce nt = -----------------------tan a Opposite = tan a × Adjacent Opposite a = atan ----------------------- Ad ja ce nt

6-10


Examples of Sine, Cosine, and Tangent Formulas



c = 90°

b A (Opposite)


Solve for the following: 1.

a = 60° A = 30 B= ? C=?

2.

A = 25 C = 50 a = ?° B=?

3.

C = 1200 a = 23° 15’ A=? B=?

4.

A = 36 B = 67 a = ?° C=?

5.

C = 3820 B = 988.69 a = ?° A=?

6-11


Problem 1 a = 60°

A(Opposite) = 30

A C = ---------sin a

30 C = ------------sin 60

30 C = ---------------------0.866025

C = 34.64

B = cos a × C

B = cos 60 × 34.64

B = 0.50 × 34.64

B = 17.32

a = 30 °

a = 60° A = 30 B = 17.32 C = 34.64

Problem 2 A(Opposite) = 25

C(Hypotenuse) = 50

A a = asin ---C

25 a = asin -----50

a = asin 0.50

B = cos a × C

B = cos 30 × 50

B = 0.866025

× 50

B = 43.30

A = sin a × C A = sin 23 ° 15 ′ × 1200

A = 0.394744

× 1200

A = 473.69

B = cos a × C B = cos 23 ° 15 ′ × 1200

B = 0.918791

× 1200

B = 1102.55

A = 25 C = 50 a = 30° B = 43.30

Problem 3 C(Hypotenuse) = 1200

a = 23° 15’

C = 1200 a = 23° 15’ A = 473.69 B = 1102.55

6-12


Problem 4 A(Opposite) = 36

B(Opposite) = 67

A a = atan -- B

36 a = atan -----67

a = atan 0.537313

a = 28.25

A C = ---------sin a

36 C = --------------------sin 28.25

36 C = ------------------------0.0473320

C = 76.06

A = 36 B = 67 a = 28.25° C = 76.06

Problem 5 C(Hypotenuse) = 3820

B(Adjacent) = 988.69

B a = acos ---C

988.69 a = acos ---------------3820

a = acos 0.258819

A = sin a × C

A = sin 75 × 3820

A = 0.965926

B = 988.69 C = 3820.00 a = 75.00° A = 3689.84

6-13

× 3820

a = 75.00

A = 3689.84


Pythagorean Theorem The square of the hypotenuse is equal to the sum of the squares of the other two sides. C 2 = A2 + B2 and C =

2

A + B

2

Thus, knowing the lengths of two sides in a right triangle, you can find the length of the third side.

a 0 3 =

C=?

B

c = 90°

b A = 51.96

Figure 8 Right triangle showing sides opposite angles

C 2 = A2 + B2 and C = 2

2

A + B

2

2

C =

51.96 + 30

C =

2699.84 + 900

C =

3599.84

C = 60

Note: This is how you calculate horizontal displacement or closure from the rectangular coordinates.

6-14


Circles

O

B

D

R

A

C

Figure 9 A circle

A circle is a figure consisting of all points located the same distance R from a fixed point O called its center. In this figure, the segment OA is the radius. The distance around the circle is called the circumference C and is calculated using C = 2 × π × R .

6-15


The Tangent TE , in the illustration below, is a tangent to the circle. It touches the circle at only one point ( E ), the point of tangency. The tangent forms a right angle with the radius of the circle ( R) at the point of tangency, because the radius is the shortest distance from the tangent to the center of the circle.

E

R

Figure 10 Tangency

6-16

T


The Arc An arc is a portion of a 360 o circle. For any angle, the ratio of an arc to the circumference is the same as the ratio of the angle to 360 o.

R

R

B

O a

R C A

Figure 11 An arc 2π × R × a 360 °

π×R×a 180°

In the illustration above, arc AB = ------------------------- = ---------------------If R = 25m and a = 40o, the circumference (C ) can be calculated using the equation below. C = 2 π × R = 2 π × 25 = 157.08m

The arc AB can be calculated using the equation below. 2π × R × a 360 °

2 π × 25 × 40 360 °

arc AB = ------------------------- = ------------------------------- = 17.45m

If R = 50 ft and a = 60o, the circumference (C ) can be calculated using the equation below. C = 2π × R =

π × 50 = 314.16 ft

The arc AB can be calculated using the equation below. 2π × R × a 360 °

2 π × 50 × 60 360 °

arc AB = ------------------------- = ------------------------------- = 52.36 ft

6-17

Well Planning Module Objectives

Well Planning Directional drillers require a knowledge of basic math concepts, including a minimum competence in algebra, geometry, and trigonometry. You generally perform any calculations required at the rigsite using a computer or programmable calculator, but it is useful to check them by hand.

Module Objectives Understand well reference points with respect to lease boundaries. Differentiate among partial coordinates, rectangular coordinates, and polar coordinates. Identify the factors determining kick-off point, maximum inclination, and build/ drop rates. Calculate the radius of curvature. Calculate various sections of a well. Calculate the toolface setting required to project ahead. Convert rectangular coordinates to polar coordinates. Calculate dogleg.

6-18

Well Planning Leaseline or Boundaries

Leaseline or Boundaries In some countries, oil and gas leases are sold. These leases are normally administered by local governing bodies or agencies and have clearly defined boundaries. Any point within a lease can be defined in terms of distance from any two adjoining boundaries.

Northern Boundary Surface Location

y r a d n u o B n r e t s e W

s e d r y o p o P r o a j e c t T r

y r a d n u o B n r e t s a E

Target Southern Boundary Figure 1

Lease boundaries

Hardlines

Lines drawn on the plot which should not be crossed for geological and legal reasons.

Land Locations

Planning a directional well presupposes some limiting factors in the positioning of the surface location. With land wells, the surface location of the well will usually be determined by the factors originally prompting the decision to drill a directional well as opposed to a vertical well.

Offshore Locations

The main difference between positioning a surface location on land and offshore is that offshore directional programs tend to be drilled from multiwell structures and are not normally as restricted as on land (mountains, jungles, cities, etc.). In most cases, an offshore drilling rig can be placed anywhere above a reservoir. The decision concerning the placement of the surface structure tends to be more affected by reservoir management considerations than geographic necessity.

6-19

Well Planning Bottomhole Targets

Bottomhole Targets Geological Requirements

The first step in planning any well is to define the objective(s). A directional well can have one or more objectives: •

Geological structures

•

Coring points

•

Geological features (such as faults or pinch outs)

•

Other wellbores (as with relief well drilling)

•

Combination of these

In this section, we look at the way in which targets are defined. As we have seen, there are various means of referring to a surface location (UTM, geographic, etc.). The same is true for the target location with the addition of the vertical depth of the target. Partial Coordinates

When planning and drilling a well, it is simpler to use partial coordinates when referring to the target. This involves using the surface location as a reference point (surface reference point) and attributing this point with the value 0,0. All other coordinates can then be referred back to this point, thus simplifying calculation and plotting procedures. The Surface Reference Point (SRP) is usually the rotary kelly bushing, the wellhead or the platform reference point. Once the exact location of the surface reference point and the target are known, the partial coordinates can easily be determined. Normally, these are either rectangular or polar.

North


Surface Location

Angle

East

D C l o i s s t a u n r e c e

Target

Rectangular Coordinate: South

Rectangular Coordinate = (East(x), South(y)) Polar Coordinate = Closure Distance at Angle° Figure 2

Rectangular/Polar coordinates

6-20


Surface Location UTM Coordinates 62,355,000 N (N/S), 5,262,544 E (E/W) North

UTM Coordinates 5,262,744 E Rectangular Coordinate: East

UTM Coordinates 62,354,500 N

Figure 3

Rectangular Coordinates

East

Target Rectangular Coordinate: South

Rectangular coordinates

Rectangular coordinates are usually given in feet/meters north or south and east or west of the SRP. They can easily be derived by subtracting the UTM coordinates of the SRP from those of the target. For example: N/S (feet)

E/W (feet)

UTM Coordinates Target

62,354,500.00 N

5,262,744.00 E

UTM Coordinates Surface

62,355,000.00 N

5,262,544.00 E

Partial Coordinates

-500.00

200.00

A positive value denotes north or east; a negative value denotes south or west. The target in the above example is 500 feet south (-ve) and 200 feet east (+ve) of the SRP.

6-21


North Surface Location

200 East D C l o i s s t a u n r e c e

Angle

500

Figure 4

Polar Coordinates

Target

Polar coordinates

Polar coordinates are derived from the rectangular coordinates and are expressed as a closure distance and a direction (either quadrant or azimuth). These are derived from the rectangular (or Cartesian) coordinates as follows: E or W Coord An gl e = atan  ---------------------------------  N or S Coord 

or, in this case: =

200 atan  ---------  500

= 21.8°

As we know, the target is south and east of the surface reference point; we know the direction of the target from the rig is: S 21.80 E in quadrant format, or 158.2° Azimuth

Closure Distance

2

E or W Coord + N or S Coord

2

, or in this case:

=

 200 2 + 500 2 = 538.5  

We can refer to our target in polar coordinates being 538.5 feet (or meters) at Azimuth 158.2°.

6-22

Well Planning Target Size

Target Size During the drilling phase of a directional well, the trajectory of the wellbore in relation to the target is constantly monitored. Often, costly decisions have to be made in order to ensure that the objectives of the well are met. A well-defined target is essential in making these decisions. The technology available today allows us to drill extremely accurate wells. The cost of drilling the well is largely dependent on the accuracy required, so the acceptable limits of the target must be well-defined before the well is commenced. Cost versus accuracy is the key consideration. In many cases, operating companies adopt an arbitrary in-house target size (or radius of tolerance), particularly in multi-well projects. The size of the target radius often reflects the convention rather than the actual geological requirements of the well. It is common for specific restrictions or hard lines to be specified only when they depict critical features such as: •

Fault lines

•

Pinch outs

•

Legal restrictions

•

Lease line boundaries

Many directional wells have been unnecessarily corrected or sidetracked in order to hit a target radius which, in fact, did not represent the actual objective of the well.

Kick-off Point The kick-off point is the vertical depth where the well is deviated in a specific direction, inclination and build rate. The kick-off point is determined by: •

Well path

•

Formation type

•

Formation pressure

6-23

Well Planning Maximum Inclination

Maximum Inclination Maximum inclination is determined by: •

KOP and target location

•

Formation characteristics

•

Hole cleaning

Build/Drop Rates Build/drop rates are determined by: •

Formation characteristics (hard/soft)

•

Deflection tools available

•

Mechanical limitations of the drillstring or casing

•

Mechanical limitations of the downhole instrumentation

•

Mechanical limitations of the production string or equipment

•

Key seats

Common build rates range from 1° to 3°/100 ft (30m) for traditional wells. Horizontal or extended reach wells may have build rates of well over 100 o /100 ft (30 m) in short radius applications.

6-24

Well Planning Basic Principle: Right Triangle

Basic Principle: Right Triangle

a C B

c = 90°

b A

Figure 5

1.

Basic principle of the right triangle

Opposite sin a = ---------------------------Hypotenuse

or

Opposite Hypotenuse = --------------------sin a

or

Opposite = sin a 2.

× Hypotenuse

Adjacent cos a = ---------------------------Hypotenuse

or

Adjacent Hypotenuse = --------------------cos a

or

Adjacent = cos a × Hypotenuse 3.

Opposite tan a = --------------------Adjacent

or

Opposite Adjacent = --------------------tan a

or

Opposite = tan a × Adjacent 4.

A a = atan -- B

5.

C = A + B

2

2

B b = atan -- A

or 2

or

C =

6-25

2

A + B

2

Well Planning Calculating the Radius of Curvature

Calculating the Radius of Curvature Knowing the build-up rate ( BUR), you can calculate the value of the radius of curvature, Rc, for the build-up section of a well. Knowing the values for inclination at the start of the arc ( I 1) and the end of the arc ( I 2), you can find the incremental values for horizontal displacement ( HD ), vertical depth (VD ), and measured depth ( MD).

The radius of curvature is normally expressed in degrees/100' (degrees/30 m). To calculate a build or drop radius, the formula is:

Feet

Meters

180 --------- × 100 π Radius = ------------------------Build Rate

180 Note: --------- × 100 = 5729.5780

π

180 --------- × 30 π Radius = ------------------------Build Rate

180 --------- × 30 = 1718.8734

π

In our examples, we will use approximate values of 5730 and 1719.

6-26


KOP (Kick Off Point) ) h t p e D l a c i t r e V e u r T (

u s i a d R

D V T

Displacement

Figure 6

Radius of curvature - relationships among angles

Feet

Meters

180 --------- × 100 5730 π Radius = ------------------------- = -----------Build Rate BUR

180 --------- × 30 1719 π Radius = ------------------------- = -----------Build Rate BUR

1.

Radius = TVD = Displacement

Radius = TVD = Displacement

2.

5730 BUR = -----------TVD

1719 BUR = -----------TVD

3.

5730 BUR = -------------------------------Displacement

1719 BUR = -------------------------------Displacement

4.

∆ Inc × 100Curve Length = -------------------------BUR

∆ Inc × 30Curve Length = ----------------------BUR

6-27


KOP 2

TVD1

s i u d a R

M D 1

R 1

3

DISP1 1

Displacement Figure 7

Calculation example

Determine TVD1, DISP1, and MD1 On the plot, Angle 1 is the angle at the end of the build. Prove Angle 1(end of build angle) = Angle 2(∆ Inclination) . 1.

180 ° = Right Angle + Angle 3 + Angle 2 and

2.

180 ° = Right Angle + Angle 3 + Angle 1

Subtract 1 from 2. 180 ° – 180 ° = Right Angle + Angle 3 + Angle 2 – Right Angle – Angle 3 – Angle 1 0 = Angle 2 – Angle 1

Add Angle 1 to both sides of the equation. 0 + Angle 1 = Angle 2 – Angle 1 + Angle 1

Complete the addition. Angle 1 = Angle 2

6-28


KOP

DISPB

DISP A 2

u s i a d R

M D

TVD1

1

R 1

3

DISP1 1

Displacement Figure 8

Calculation example

Determine:

Calculate:

1.

TVD 1

1. R 1

2.

DISP1

2. DISPB

3.

MD 1

Calculate:

Formulas used:

× Radius

Opposite = sin a × Hypotenuse

1.

TVD 1 = sin Angle 2

2.

DISP A = cos Angle 2 × Radius

3.

DISP 1 = Radius – ( cos Angle 2 × Radius )

4.

∆ Inc × 100MD 1 = -------------------------BUR

Note: DISP 1 = DISP B

6-29

Adjacent = cos a × Hypotenuse

Calculating a Directional Well Plan Basic Principle Right Triangle

a

C

A

c

b B

1. 2.

2

A + B

2

2

= C and C =

2

A + B

2

Opposite sin a = ------------------------------ Hyp oten use

or

Opposite = sin a × H yp ot en us e

or

Opposite Hypotenuse = -----------------------sin a 3.

Adjacent cos a = ------------------------------ Hypoten use

or

Adjacen t = cos a × H yp ot en us e

or

Adjacent Hypotenuse = ----------------------cos a B a = atan -- A 4.

Opposite Adjace nt = -----------------------tan a 5.

A c = atan -- B

Opposite = Adjacent × tan a 6-30

Calculating a Directional Well Plan Basic Principle Calculate the radius of curvature (normally expressed in degrees/100’ (30 m). To calculate a build or drop radius the formula is:

180 --------- × 100 π Radiu s = --------------------------- Build Rate

6-31

Calculating a Directional Well Plan

Feet

Meters

180 --------- × 100 π 5730 R = ------------------------ = ----------- BUR BUR

180 --------- × 30 π 1719 R = --------------------- = ----------- BUR BUR

1.

Radiu s = TVD = Displace ment

Ra diu s = TVD = Di spla cemen t

2.

5730 BUR = -----------TVD

1719 BUR = -----------TVD

3.

5730 BUR = ------------- DISP

1719 BUR = ------------- DISP

4.

∆ Inc × 100 Curve Length = -------------------------- BUR

∆ Inc × 30 Curve Len gth = ----------------------- BUR

6-32


KOP 2

R S U I D A R

M D 1

TVD1

3

DISP1 1

DISPLACEMENT

If you do not build from 0° – 90°: Determine TVD1, DISP1, and MD1 On the plot, Angle 1 is the angle at the end of the build. Note: °

180 = Right Angle + Angle 2 + Angle 3 and °

180 = Angle 1 + Right Angle + Angle 3 therefore Angle 1 = Angle 2

6-33


KOP

DISPB

DISPA 2

R S U I D A R

M D 1

TVD1

3

DISP1 1

DISPLACEMENT

Determine: 1.

TVD1

2.

DISP1

3.

MD1

Opposite = sin a × Hypotenuse TVD 1 = sin Angle 2 × Radius Adjacent = cos a × Hypoten use DISP A = cos Angle 2 × Radius DISP B = Radius – ( cos Angle 2 × Radius ) DISP 1 = DISP B ∆ Angle × 100 MD 1 = --------------------------------- BUR

6-34

Calculating a Directional Well Plan Example 1 Given: 1. 2. 3.

Build Rate = 1.5°/100' Drop Rate = 1.0°/100' EOB =30°

180 --------- × 100 π R = ----------------------- BUR

SL

R 1 = 3820 ∆ TVD 2 = sin 30 ° × 3820

KOP TVD1

TVD 2 = 1910 M D

R 1

( 0 ° – 30 ° ) × 100 MD 1 = ---------------------------------------1.5

1

TVD2

MD 1 = 2000

DISP1

DISP 1 = Radius – ( cos 30 ° × 3820 ) DISP 1 = 511.78

TVD3 DISP2

R 2

M D 3

R 2 = 5730 ∆ TVD 4 = 2865

TVD4 DISP3

DISP 3 = 767.76 MD 3 = 3000

6-35

Calculate a Well Proposal Type 1 Well (Build and Hold) Profile # 1

Given: 1. 2. 3. 4. 5. 6.

Calculate:

Surface Location Start Inclination = 0° Target TD = 9000' Target Displacement = 5000' Maximum Inclination = 40° Build Rate = 2°/100'

1. 2. 3. 4. 5. 6. 7. 8.

SL

9.

TVD1 TVD2 DISP1 MD1 MD2 Total MD KOP TVD3 DISP2

KOP TVD1

MD1

R1

TVD2 DISP1

MD2

TVD3

Total DISP2

6-36

Calculate a Well Proposal Type 1 Well (Build and Hold) Profile # 1

Calculate R1

5730 = ----------- BU B U R

= 2865

Calculate ýTVD 2

= sin a × H y p otenuse

= 1841.59

Calculate DISP1

yp ot o t en en us u s e) = R 1 – ( cos a × H yp

= 670.28

Calculate MD 1

A n g le × 100 ∆ An = --------------------------------- BU B U R

= 2000

Calculate DISP2

Targeet DISP DISP – DISP 1 = Targ

= 5000 – 670.28

= 4329.7

Calculate ýTVD 3

Opposite = -----------------------tan a

= 5159.96

Calculate KOP

= ( ∆ T V D 3 + ∆ T V D 2 ) – Target TVD = 1998.45

Calculate MD 2 Calculate Total MD

Opposite = -----------------------sin a M D 1 + M D 2 + K O P = MD

6-37

= 6735.85 = 10734.30

Calculate a Well Proposal Type 1 Well (Build and Hold) Calculate:

Given:

Profile # 2

1. 2. 3. 4. 5. 6.

Surface Location Start Inclination = 0° KOP = 3200' Target TVD = 12500' Target Displacement = 5000' Build Rate = 2°/100'

1. 2. 3. 4. 5. 6. 7. 8. 9.

SL

TVD1 TVD2 TVD3 DISP1 DISP2 Inclination at EOB MD1 MD2 Total MD

KOP TVD1

MD1

R1

TVD2 DISP1

MD2

TVD3

Total DISP2

6-38

Calculate a Well Proposal Profile # 2

SL

SL

KOP

KOP

TVD1

TVD1

MD1

1

R1

R1

MD1 TVD2 DISP1

TVD2 DISP1 5 L1 3

MD2

L2

4

TVD3

Total

2

DISP2

TVD3 DISPB

DISP1 DISP2

Calculate R1 Calculate DISP3

5730 = ----------- BU B U R Target et DISP DISP – R1 = Targ

= 3820 = 8500 – 3820 = 4680

Calculate L 1

Target et TVD TVD – KOP = Targ

= 12 500 – 3200

Calculate Angle 1

DIS D IS P B = atan ---------------- L 1

= 9300

Calculate L 2

Calculate Angle 2

=

2

= 26.71 ° 2

DI D I S P B + L 1

R 1 = asin ----- L 2

= 10411.17

= 21.53 °

6-39

Calculate a Well Proposal Profile #2 SL

KOP TVD1 1 R1

MD1

TVD2 DISP1 5 L1 3

L2

4

2 TVD3 DISPB

DISP1 DISP2

Calculate Angle 5 Where: 1.

180° = Angle 1 + Angle 2 + Angle 3

and 2.

180° = Angle 3 + Angle 4

and subtracting 1 from 2 0° = Angle 1 + Angle 2 - Angle 4 and moving Angle 4 to the other side Angle 4 = Angle 1 + Angle 2 Since Angle 4 and Angle 5 are created by a vertical line intersecting the hold section, Angle 4 = Angle 5, then Angle 5 = Angle 1 + Angle 2 Angle 5 = 48.5° 6-40

Calculate a Well Proposal SL

KOP TVD1 1 R1

MD1

TVD2 DISP1 5 L1 3

L2

4

2 TVD3 DISPB

DISP1 DISP2

Calculate ýTVD 2

= sin a × H y p otenuse = 48.24 × 3820

= 2849.50

Calculate DISP1

yp ot o t en en us us e) = R 1 – ( cos a × H yp

= 1275.84

Calculate MD1

A n g l e × 100 ∆ An = --------------------------------- BU B U R

= 3216

Calculate ýTVD 3

= L 1 – ∆ T V D 2

Calculate DISP2 Calculate MD2

= 9300 – 2849.50

= 6450.50

Targett Displ Displace aceme ment nt – DISP DI SP 1 = Targe

= 7224.16

= =

2

DI D I S P B + ∆ T V D 3 2

2

7224.16 + 6450.50

6-41

2

= 9684.91

Calculate a Well Proposal Type 1 Well (Build and Hold)

Calculate a Well Proposal Profile # 2

KOP TVD1

MD1

R1

TVD2 DISP1

MD2

TVD3

Total DISP2

TVD1

=

3200.00

TVD2

=

6049.50

TVD3

= 12500.00

DISP1

=

1275.84

DISP2

=

7224.16

Inc at EOB =

48.24°

MD1

=

3216.00

MD2

=

9684.91

Total MD

= 16100.91 6-42

Target Approach Calculations The diagram below indicates that the direction from the surface location to the center of the target at the given true vertical depth (TVD) is along an azimuth of 29 o. The distance from the surface location along a straight line to the target center on the horizontal section is 500 meters. This distance (500 meters) can also be described as a distance along a direction (polar coordinate) or as a direction and a magnitude (vector).

Eastings -50

0

50

100

150

200

250

300

350 500

Target 450

29 degrees 400

0 0 5

m

350

300

Target Center = 500 meters at 29°

250

200

150

100

50

0

1 0 m

Surface Location

10 m -50

Figure 1

6-43

N o r t h i n g s

You may also calculate the target boundary using rectangular coordinates. In this instance, a distance of 500 meters along 29 o would then be shown as a point described as 437.31 meters N (because the direction is north if its sign is positive and directionally known as latitude) and 242.40 meters E (because the direction is east if its sign is positive and directionally known as departure.

Eastings -50

0

50

100

150

200

250

300

350 500

450

242.40 m E

400

0 0 5 4 3 7 . 3 1 m N

m

350

300

Target Center = 250

500 meters at 29°

N o r t h i n g s

200

OR 242.40 m E 437.31 m N 29°

150

100

50

0

1 0 m

10 m -50

E/W = Opposite = sin(Angle) x Hypotenuse

N/S = Adjacent = cos(Angle) x Hypotenus

E/W = sin(29) x 500

N/S = cos(29) x 500

E/W = 0.484810 x 500

N/S = 0.874620 x 500

E/W = 242.404810

N/S = 437.309854

E/W = 242.40 m E

N/S = 437.31 m N

Figure 2

6-44

As shown below, North and East are positive signs and South and West are negative signs.

Eastings -400

-300

-200

-100

0

100

200

300

400 500

Target Center =

400

500 meters at 29°

300

29 degrees

OR 200

242.40 m E 437.31 m N

100

0

N o r t h i n g s

-100

-200

-300

-400

2 0 m

20 m -500


N/S = Adjacent = cos(Angle) x Hypotenuse

E/W = sin(29) x 500

N/S = cos(29) x 500

E/W = 0.484810 x 500

N/S = 0.874620 x 500

E/W = 242.404810

N/S = 437.309854

E/W = 242.40 m E

N/S = 437.31 m N

Figure 3

6-45

A 400 meter distance along a direction of 137 o equals 272.80 meters East (+) and 292.54 meters South (-).

Eastings -400

-300

-200

-100

0

100

200

300

400 500


400 Target Center = 500 meters at 29° OR 242.40 m E 437.31 m N

OR

300

200

272.80 m E 292.54 m S

100

137 degrees

0

N o r t h i n g s

-100

-200

-300

-400

2 0 m

20 m -500



E/W = sin(137) x 400

N/S = cos(137) x 400

E/W = 0.681998 x 400

N/S = -0.731354 x 400

E/W = 272.799344

N/S = -292.541481

E/W = 272.80 m E

N/S = 292.54 m S

Figure 4

6-46

A 450 meter distance along a direction of 219 o equals 283.19 meters West (-) and 349.72 meters South (-).

Eastings -400

-300

-200

-100

0

100

200

300

400 500

400


Target Center = 500 meters at 29° OR 242.40 m E 437.31 m N

OR

300

200

283.19 m W 349.72 m S

100

0

219 Degrees

N o r t h i n g s

-100 Target Center = 400 meters at 137° OR -200 272.80 m E 292.54 m S

-300

-400

2 0 m

20 m -500



E/W = sin(219) x 450

N/S = cos(219) x 450

E/W = -0.629320 x 450

N/S = -0.777146 x 450

E/W = -283.194176

N/S = -349.715683

E/W = 283.19 m W

N/S = 349.72 m S

Figure 5

6-47

A 390 meter distance along a direction of 347 o equals 87.73 meters West (-) and 380.00 meters North (+).

Eastings -400

-300

-200

-100

0

100

200

300

400 500

Target Center =

400 Target Center = 500 meters at 29° OR 242.40 m E 437.31 m N

390 meters at 347° OR

300

200

87.73 m W 380.00 m N

100

0

347 Degrees

N o r t h i n g s

-100 Target Center = 400 meters at 137° OR -200 272.80 m E 292.54 m S

-300 Target Center = 450 meters at 219° OR 283.19 m W 349.72 m S

-400

2 0 m

20 m -500



E/W = sin(347) x 390

N/S = cos(347) x 390

E/W = -0.224951 x 390

N/S = 0.974370 x 390

E/W = -87.730911

N/S = 380.004325

E/W = 87.73 m W

N/S = 380.00 m N

Figure 6

6-48

Since we can use polar/rectangular coordinates from surface to the center of the target, we can also use this same calculation to determine the coordinates from the target center to any point on the circumference of the target circle. Generally speaking, on a conventional directional well, we wish to know the points on the target that are known as the high side, low side, left side, and right side. We want to be able to calculate the coordinates that would place us inside the constraint of the 30 meter radius. in order to be within the target, we need to calculate the coordinates that would place us inside the 30 meter radius constraint.

Eastings -50

0

50

100

150

200

250

300

350 500

Left Side

Target Center is 500 meters at 29° 242.40 m E 437.31 m N

Target Center

High Side 450

Right Side 400

Low Side 350

300

250

N o r t h i n g s

200

150

100

50

0

1 0 m

Surface Location

10 m -50

Figure 7

The center of the target is 500 meters along a 29 o azimuth. If we subtract 30 meters from 500, we will arrive at the low side. 470 meters along a 29 o azimuth

6-49

is 227.86 meters East (+) and 411.07 meters North (+).

Eastings -50

0

50

100

150

200

250

300

350 500

Left Side


High Side 450

Right Side

Target Center

400

Low Side 350

300

250

N o r t h i n g s

200

Low Side = 470 meters at 29° 227.86 m E 411.07 m N

150

100

50

0

1 0 m

Surface Location

10 m -50



E/W = sin(29) x 470

N/S = cos(29) x 470

E/W = 0.484810 x 470

N/S = 0.874620 x 470

E/W = 227.860522

N/S = 411.071262

E/W = 227.86 m E

N/S = 411.07 m N

Figure 8

6-50

Using the same criteria to determine the high side, we would use 530 meters along a 29o azimuth, or 256.95 meters East (+) and 463.55 meters North (+).

Eastings -50

0

50

100

150

200

250

300

350 500


Left Side

High Side 450

Right Side

Target Center

400

Low Side 350

300

High Side = 530 meters at 29° 256.95 m E 463.55 m N

Low Side = 470 meters at 29° 227.86 m E 411.07 m N

250

N o r t h i n g s

200

150

100

50

0

1 0 m

Surface Location

10 m -50



E/W = sin(29) x 530

N/S = cos(29) x 530

E/W = 0.484810 x 530

N/S = 0.874620 x 530

E/W = 256.949099

N/S = 463.548445

E/W = 256.95 m E

N/S = 463.55 m N

Figure 9

6-51

Two methods exist to mathematically determine the coordinates to the right or left hand sides of the target circle. The first method uses the two given outlined in the directional plot/proposal to construct a right triangle. The distance from the surface location to the target center is 500 meters and the distance of the target radius is 30 meters. The right and left side points are at 90 o from the proposed direction of 29 o. This 30 meter length (target radius) and the 500 meter length (distance from the surface to target center) form two legs of a right triangle. Using the Pythagorean theorem, you can determine the length of the hypotenuse of this triangle. Using the inverse tangent geometric formula, you can determine the angle formed between the long leg and the hypotenuse. This angle is the difference between the distance and angle to the center of the target and the distance and angle to the left AND right side of the target. This angle difference is SUBTRACTED from the proposed direction to arrive at the direction to the left side point and ADDED to arrive at the right side point. We now have the angle of the l eft and right side points on the target circumference and a distance to these points (the hypotenuse).

Eastings -50

0

50

100

150

200

250

300

350 500


Left Side

3 0 m

450

Right Side 400

m

0 9 . 0 m 0 0 0 5 5 = e s u n e t o p y H

350

300

250

N o r t h i n g s

200

a = 3.43°

a 150

100

50

0

1 0 m

Surface Location

10 m -50

Angle a = atan = Opposite/Adjacent

Hypotenuse = C = Adjacent/(cos a)

atan = 30/500

C = 500/(cos 3.43)

atan = 0.06000

C = 500/0.998209

a = 3.433630°

C = 500.897288

a = 3.43°

C = 500.90 m

Figure 10

6-52

If you subtract 3.43 o from the proposed direction, you obtain the left side direction of 25.57o. Combining this direction with the length of the hypotenuse (500.90 meters) allows you to convert polar to rectangular coordinates. Conversely, if you add 3.43 o from the proposed direction, you obtain the right side direction of 32.43 o and can convert from polar to rectangular coordinates.

Eastings -50

0

50

100

150

200

250

300

350 500


Left Side

3 0 m

450

Right Side 400

e s u n e t o p y H

m 0 9 . 0 m 0 0 0 5 5 =

350

300

Left Side is 500.90 meters at 25.57°

250

N o r t h i n g s

200

a = 3.43°

a

Right Side is 500.90 meters at 32.43°

150

100

50

0

1 0 m

Surface Location

10 m -50

Left side angle = Target center - a

Right side angle = Target center + a

Left side angle = 29 - 3.43

Right side angle = 29 + 3.43

Left side angle = 25.57°

Right side angle = 32.43°

Left Side Distance = Hypotenuse

Right Side Distance = Hypotenuse

Left Side Distance = 500.90 meters

Right Side Distance = 500.90 meters

Figure 11

6-53

500.90 meters along an azimuth of 25.57 converts to 451.84 m North (Latitude) a nd 216.20 m East (Departure). Eastings -50

0

50

100

150

200

250

300

350 500


Left Side

3 0 m

450

Right Side 400

0 9 . 0 0 5

m

0 0 5

m

350

300

Left Side is 500.90 meters at 25.57° 216.20 m E 451.84 m N

3.43°

Right Side is 500.90 meters at 32.43°

250

N o r t h i n g s

200

150

100

50

0

1 0 m

Surface Location

10 m -50

E/W = sin(Angle) x Hypotenuse

N/S = cos(Angle) x Hypotenuse

E/W = sin(25.57) x 500.90

N/S = cos(25.57) x 500.90

E/W = 0.431613 x 500.90

N/S = 0.902059 x 500.90

E/W = 216.195198

N/S = 451.841174

E/W = 216.20 m E

N/S = 451.84 m N

Figure 12

6-54

500.90 meters along an azimuth of 32.43 o converts to 422.78 m North (Latitude) and 268.62 m East (Departure).

Eastings -50

0

50

100

150

200

250

300

350 500


Left Side

3 0 m

450

Right Side 400

0 9 . 0 0 5

m

0 0 5

m

350

300

Left Side is 500.90 meters at 25.57° 216.20 m E 451.84 m N

3.43°

Right Side is 500.90 meters at 32.43° 268.62 m E 422.78 m N

250

N o r t h i n g s

200

150

100

50

0

1 0 m

Surface Location

10 m -50



E/W = sin(32.43) x 500.90

N/S = cos(32.43) x 500.90

E/W = 0.536269 x 500.90

N/S = 0.844047 x 500.90

E/W = 268.617047

N/S = 422.783268

E/W = 268.62 m E

N/S = 422.78 m N

Figure 13

6-55

You may also calculate coordinates by working within the target circle. This method is longer, but demonstrates that there are two ways to arrive at the same answer, and also acts as a check system. Here we find the rectangular coordinates of the left and right sides of the target circle by using polar c oordinate data. The direction is defined by the addition and subtraction of 90 o to the proposed direction and the distance is defined by the target radius. When you identify the coordinates that are 30 meters along 90 o left and right of the target center point, you can calculate their coordinates relative to the surface location. 90o added to the target direction of 29 o equals 119o, and 90o subtracted from 29 o equals 299o.

Eastings -50

0

50

100

150

200

250

300

30 m


350 500

30 m

299°

299°

Left Side

29°

29° 450

119° Right Side

Left Side

400

350

119° 300

N o r t h i n g s

Right Side 250

200

150

100

50

0

1 0 m

Surface Location

10 m -50

Left Side angle = Target Direction - 90

Right Side angle = Target Direction + 90

Left Side angle = 29 - 90

Right Side angle = 29 + 90

Left Side angle = 299°

Right Side angle = 119°

Figure 14

6-56

Converting polar to rectangular coordinates, gives you the following calculati ons:

Eastings

-50

Left Side is 30 m at 299° 26.24 m W 14.54 m N 0

50

100

150

200

250

300

Left Side is 30 m at 299° 26.24 m W 14.54 m N


299°

30 m

350

500

450

119°

400

299°

350

300

119°

30 m

250

N o r t h i n g s

200

150

100

50

0

1 0 m

Surface Location

10 m -50



E/W = sin(299) x 30

N/S = cos(299) x 30

E/W = -0.874620 x 30

N/S = 0.484810 x 30

E/W = -26.238591

N/S = 14.544289

E/W = 26.24 m W

N/S = 14.54 m N

Figure 15

6-57

Eastings

Right Side is 30 m at 119° 26.24 m E 14.54 m S

-50

0

50

100

150

200

250

300



500

299°

30 m

350

450

119°

400

299°

350

300

119°

30 m

250

N o r t h i n g s

200

150

100

50

0

1 0 m

Surface Location

10 m -50



E/W = sin(119) x 30

N/S = cos(119) x 30

E/W = 0.874620 x 30

N/S = -0.484810 x 30

E/W = 26.238591

N/S = -14.544289

E/W = 26.24 m E

N/S = 14.54 m S

Figure 16

6-58

These are the coordinates from the surface location (0 meters North and 0 meters East) to the left side of the ta rget center point. By converting from rectangular to polar coordinates, this point is defined as 500.90 meters along a 25.57 o azimuth. Checking on the horizontal section plot shows you that these coordinates are, in fact, correct.

Eastings -50

0

50

100

150

200

250

300

350 500



450


400

350

300

Left Side is 216.16 m E 451.85 m N

250

N o r t h i n g s

200

150

100

50

0

1 0 m

Surface Location

10 m -50

E/W = Target E/W + Left Side E/W

N/S = Target N/S + Left Side N/S

E/W = 242.40 m E + 26.24 m W

N/S = 437.31 m N + 14.54 m N

E/W = 242.40 - 26.24

N/S = 437.31 + 14.54

E/W = 216.16 m E

N/S = 451.85 m N

Figure 17

6-59

The same calculation is used to determine the right side of the target’s coordinates.

Eastings -50

0

50

100

150

200

250

300

350 500



450


400

350

300

Left Side is 216.16 m E 451.85 m N

250

N o r t h i n g s

200

150

Right Side is 268.64 m E 422.77 m N

100

50

0

1 0 m

Surface Location

10 m -50

E/W = Target E/W + Right Side E/W

N/S = Target N/S + Right Side N/S

E/W = 242.40 m E + 26.24 m E

N/S = 437.31 m N + 14.54 m S

E/W = 242.40 + 26.24

N/S = 437.31 - 14.54

E/W = 268.64 m E

N/S = 422.77 m N

Figure 18

6-60

By knowing these coordinates, you will be able to calculate the distance and direction required to land within the target boundaries. As the directional job progresses, you will be calculating your surveys to determine where you are relative to the target. After subtracting the calculated survey latitude and departure from the coordinates of all four points (high side, low side, left side, and right side), you will convert the rectangular coordinates to polar and be left with the distance and direction to each point. Knowing the direction of your survey and the direction to the left and right side of the target constraints will determine whether corrective directional steering is required or not. Combining the distance to target and the remaining TVD (t arget TVD minus the survey calculated TVD) will allow you to use the tangent formula to calculate the required inclination to the low, center, high, left, and right sides of the target. Important:

It cannot be stressed enough that ALL calculations have to use the data EXTRAPOLATED to the bit depth and NOT the survey depth.

6-61

Vertical Section Calculation Find the center, high side, low side of the target from an inclination of 58°, with a target inclination of 60°. The current bit position at a TVD of 2728.90 m and a Vertical Section of 400 m. The target center is at a TVD of 2784.90 m and a Vertical Section of 500m. The target radius is 30 m.

Figure 19

6-62

Figure 20

Calculate the ∆TVD and ∆VS (Vertical Section) of target center:

∆ TVD

= T arg etT V D – C u rr e nt T VD

∆ VS

= T arg etVS – CurrentVS

∆ TV D

= 2784.9 – 2728.90

∆ VS

= 500 – 400

∆ TV D

= 56.00

∆ VS

= 100

Figure 21

6-63

Figure 22

Calculate the ∆TVD and ∆VS of the high side of the target:

∆ TVD


∆ VS HS

=

∆ TV D

= 2784.9 – 2728.90

∆ VS HS

= 100 + 30

∆ TV D

= 56.00

∆ VS HS

= 130

Figure 23

6-64

∆ VS + T arg etRadius

Figure 24

Calculate the ∆TVD and ∆VS of the low side of the target:

∆ TVD


∆ VS LS

=

∆ TV D

= 2784.9 – 2728.90

∆ VS LS

= 100 – 30

∆ TV D

= 56.00

∆ VS LS

= 70

Figure 25

6-65

∆ VS – T arg etRadius

Figure 26

Calculate the Angle and distance to the target center: Method 1 MD =

∆ TV D 2 + ∆ VS 2

MD =

56 + 100

2

∆ VS Angle = asin ---------- MD

2

MD =

3136 + 10000

100 An gl e = asin ---------------114.61

MD =

13136

Angle = asin 0.872524 Angle = 60.75 °

MD = 114.61 m

Method 2

∆ VS An gl e = atan ---------------∆ TV D

∆ VS MD = ----------------------sin An gl e

100 An gl e = atan --------56

100 MD = --------------------sin 60.75

An gl e = atan 1.785714

100 MD = ---------------------0.872496

An gl e = 60.75 °

MD = 114.61 m

6-66

Figure 27

Calculate the Angle and distance to the high side of the target: Method 1 MD =

∆ TV D 2 + ∆ VS HS 2

MD =

56 + 130

2

∆ VS HS Angle = asin ---------------- MD

2

MD =

3136 + 16900

130 An gl e = asin ---------------141.55

MD =

20036

Angle = asin 0.918403 Angle = 66.69 °

MD = 141.55 m

Method 2

∆ VS An gl e = atan ---------------∆ TV D

∆ VS MD = ----------------------sin An gl e

130 An gl e = atan --------56

130 MD = --------------------sin 66.70

An gl e = atan 2.321429

130 MD = ---------------------0.918446

An gl e = 66.70 °

MD = 141.54 m

The difference is a minor rounding error between Method 1 and Method 2. Method 1

Method 2

Angle = 66.693717° MD = 141.548578 m

Angle = 66.695113° MD = 141.543374 m

6-67

Figure 28

Calculate the Angle and distance to the low side of the target: Method 1

∆ VS LS Angle = asin --------------- MD

MD =

∆ TV D 2 + ∆ VS LS 2

MD =

56 + 70

MD =

3136 + 4900

70 Angle = asin ------------89.64

MD =

8036

Angle = asin 0.780901

2

2

Angle = 51.34 °

MD = 89.64 m

Method 2

∆ VS LS An gl e = atan ---------------∆ TV D

∆ VS LS MD = ----------------------sin An gl e

70 An gl e = atan -----56

70 MD = --------------------sin 51.34

An gl e = atan 1.250000

70 MD = ---------------------0.780867

An gl e = 51.34 °

MD = 89.64 m

6-68

Target Approach Project Current Location:

Target Location:

1. 2. 3. 4.

1. 2. 3. 4. 5.

E 100 m N 250 m TVD = 2586.18 m Inclination = 46.63°

500 m at 29° TVD = 2792.50 m Inclination = 60° KOP = 2000 m Target Radius 30 m

Calculate target approach and vertical section locations.

Figure 29

6-69

Calculate the following: 1.

Target Coordinate Location

2.

Current Position Distance and Angle

3.

Partial Coordinates from Current Locat ion to Target Center

4.

Angle and Distance to Target Center from Current Location

5.

High Side Coordinates

6.

Low Side Coordinates

7.

∆Angle from Target Center to Side

8.

Right Side Coordinates

9.

Left Side Coordinates

10. Vertical Section 11. 12. 13. 14. 15. 16. 17. 18. 19.

∆Vertical Section to Target Center ∆TVD to Target Center Target Center ∆Angle and ∆MD ∆Vertical Section to High Side ∆TVD to High Side High Side ∆Angle and ∆MD ∆Vertical Section to Low Side ∆TVD to Low Side Low Side ∆Angle and ∆MD

Target Center Coordinates EW = sin An gl e × Dist

= sin 29 × 500

= 0.484810

× 500

= E 242.40 m

NS = cos A n gl e × D is t

= cos 29 × 500

= 0.874620

× 500

= N 437.31 m

Current Location Distance and Angle Method 1 Di st =

2

EW + NS

2

=

2

100 + 250

2

=

72500

= 269.26 m

100 = asin ---------------269.26

= asin 0.371388

= 21.80 °

EW An gl e = atan -------- NS

100 = atan --------250

= atan 0.400000

= 21.80 °

EW Di st = ----------------------sin An gl e

100 = --------------------sin 21.80

100 = ---------------------0.371368

= 269.27 m

EW An gl e = asin ---------- Di st

Method 2

6-70

Figure 30

Partial Coordinates EW = T arg et EW – CurrentEW

= 242.4 – 100

= E 142.40 m

NS = T arg et NS – CurrentNS

= 437.31 – 250

= N 187.31 m

Current Location Distance and Angle Method 1 Di st =

2

EW + NS

2

=

2

142.40 + 187.31

2

=

55362.80

= 235.29 m

142.40 = asin ---------------235.29

= asin 0.605211

= 37.24 °

EW An gl e = atan -------- NS

142.40 = atan ---------------187.31

= atan 0.760237

= 37.24 °

EW Di st = ----------------------sin An gl e

142.40 = --------------------sin 37.24

142.40 = ---------------------0.605155

= 235.31 m

EW An gl e = asin ---------- Di st

Method 2

6-71

Figure 31

High Side Coordinates Di st HS = Dist + 30 m = 235.29 + 30

= 265.29 m

EW = sin A × Dist HS

= sin 37.24 × 265.29 = 0.605155

× 265.29

= E 160.54 m

NS = cos A × Dist HS

= cos 37.24 × 265.29 = 0.796108

× 265.29

= N 211.20 m

Low Side Coordinates Di st LS = Dist – 30 m

= 235.29 – 30

= 205.29 m

EW = sin A × Dist LS

= sin 37.24 × 205.29 = 0.605155

× 205.29

= E 124.23 m

NS = cos A × Dist LS

= cos 37.24 × 205.29 = 0.796108

× 205.29

= N 163.43 m

∆Angle ∆ A

T arg etR = atan -------------------- Di st

30 = atan ---------------235.29

= atan 0.127502

= 7.27 °

235.29 = ---------------------acos 7.27

235.29 = ---------------------0.991961

= 237.20 m

Distance to Side Di st Di st S = ------------------acos ∆ A

6-72

Figure 32

∆Angle and Distance to Side ∆ A

T arg etR = atan -------------------- Di st

Di st Di st S = ------------------acos ∆ A

30 = atan ---------------235.29

= atan 0.127502

= 7.27 °

235.29 = ---------------------acos 7.27

235.29 = ---------------------0.991961

= 237.20 m

Right Side Coordinates A R = Angle + ∆ A

= 37.24 + 7.27

= 44.51 °

EW = sin A R × Dist S

= sin 44.51 × 237.20 = 0.701034

× 237.20

= 166.29 m

NS = cos A R × Dist S

= cos 44.51

× 237.20

× 237.20

= 169.15 m

= 0.713128

Left Side Coordinates A L = Angle – ∆ A

= 37.24 – 7.27

EW = sin A L × Dist S

= sin 44.51 × 237.20 = 0.701034

× 237.20

= 166.29 m

NS = cos A L × Dist S

= cos 44.51

× 237.20

× 237.20

= 169.15 m

6-73

= 29.97 °

= 0.713128

Figure 33

∆Vertical Section and ∆TVD to Target Center VS = cos ∆ a × Dist

∆ VS

= cos 7.2 × 269.27

= T arg etVS – CurrentVS

∆ TVD

= T arg etTVD – CurrentTVD

= 0.992115

× 269.27

= 267.15 m

= 500 – 267.15

= 232.85 m

= 2792.50 – 2624.80

= 167.70 m

Target Center ∆Angle and ∆MD

∆ An gl e ∆ MD

∆ VS = atan ---------------∆ TV D

∆ VS = --------------------------sin ∆ An gl e

232.85 = atan ---------------167.70

= atan 1.388491

= 54.24 °

232.85 = --------------------sin 54.24

232.85 = ---------------------0.811472

= 286.95 m

∆Vertical Section and ∆TVD to High Side ∆ VS HS

=

∆ VS + 30 m

∆ TVD


= 232.85 + 30

6-74

= 262.85 m = 2792.50 – 2624.80

= 167.70 m

Figure 34

High Side ∆Angle and ∆MD

∆ An gl e ∆ MD

∆ VS HS = atan ----------------∆ TV D

∆ VS HS = --------------------------sin ∆ An gl e

262.85 = atan ---------------167.70

= atan 1.567382

= 57.46 °

262.85 = --------------------sin 57.46

232.85 = ---------------------0.843016

= 311.80 m

∆Vertical Section and ∆TVD to Low Side ∆ VS LS

=

∆ VS – 30 m

∆ TVD


= 232.85 – 30

= 202.85 m = 2792.50 – 2624.80

= 167.70 m

Low Side ∆Angle and ∆MD

∆ An gl e ∆ MD

∆ VS LS = atan ---------------∆ TV D

∆ VS LS = --------------------------sin ∆ An gl e

6-75

202.85 = atan ---------------167.70

= atan 1.209600

= 50.42 °

202.85 = --------------------sin 50.42

202.85 = ---------------------0.770736

= 263.19 m


1.

Start of Job 1.1.

Compare Proposal well name and location with rig manager, Geologist and well license

1.2. 2.

3.

4.

Determining Ground and KB elevations and adjust proposal accordingly

Entering Surveys 2.1.

Tie on

2.2.

Adding surveys

2.3.

Deleting surveys

2.4.

Editing surveys

Adding Text Lines 3.1.

Review what is needed for the Final Completion Survey

3.2.

Final Completion Survey Example

3.3.

MD, TVD and Subsea methods to input Text Lines

Quick Printing 4.1.

Review options in Quick Printing

5. Graphics 5.1.

Review Plan view parameters with step sizes

5.2.

Review Side view parameters with step sizes

5.3.

Change colors of wells

5.4.

Turn Wells on and off in graphics

5.5.

Turn targets on and off in graphics

5.6.

Exaggerate the vertical to show changes in TVD in Side view

6. Targets 6.1.

Review adding targets based on Lat. & Dep. AND Closure Dist. and Closure Azimuth

6.2.

Show how to turn on the “Graph Targets” option to view targets in the plan and side views

7. Interpolating

8.

9.

7.1.

Review difference between Interpolating and Extrapolating

7.2.

Interpolating using Edit Text Lines

7.3.

Interpolating using the Quick Print

7.4.

Insert Single Interpolation - Under Tools

7.5.

Multiple Interpolations - Under Planning – Show Plan Survey

KB Adjustments 8.1.

KB vs Subsea Example with diagram

8.2.

KB vs TVD Example with diagram

8.3.

Tie on to existing build with new KB Example with diagram

8.4.

Field Example #1 Tie on to an existing build

8.5.

Field Example #2 Tie on to an existing build

8.6.

Field Example #3 Tie on to an existing lateral

8.7.

Shifting Build Surveys to reflect a new KB elevation

Projecting Ahead 9.1.

Project To Bit

9.2.

Directional Example Straight Line Projection

9.3.

Build Section Example Required Correction to Target review Radius of Curvature – BUR to Target TVD and INC Review Other Projection Methods Posting Projections Stacking Projections

10. Simple Planning 10.1.

Review Types of wells that can be planned using Simple Planning

10.2.

Plan with 2 out of 4 unknowns (step sizes)

10.3.

Plan with 2 out of 7 unknowns (step sizes)

11. Field Setup Exercise 11.1.

Set up 2 well surfaces relative to each other

11.2.

Create 2 proposals using Simple Planning

12. Anti-Collision 12.1.

Review basics of anti-collision

12.2.

Run anti-collision report for two wells: Switching the offset and reference wells Varying the Interpolation Interval Varying the scan radius Determine which well is above and below the other when the two wells cross using Tool Faces and 3-D viewer


Computalog Drilling Services - Wellz Quick Start Manual

WELLZ QUICK START INSTRUCTION MANUAL 1. INTRODUCTION The purpose of the Wellz Quick Start Instruction Manual is to provide an easy to follow, step by step guide for the Survey portion of the Wellz software. This manual outlines how to properly setup a new Wellz Survey file and utilize the software’s key features by incorporating a logical sequence of screen captures, typical examples and brief explanations. Once you have jumped into the program, a more detailed explanation of all features can be accessed through the Help section of the Wellz program.

2. CREATING A NEW SURVEY FILE Step 1:Start Wellz Double click the Wellz icon on the Desktop wellz.ico

Step 2: Select to create a new Wellz survey file

This is the “Wellz Start Up” box. Click the New button to create a new Wellz file.

Note: Once the Wellz file has been created, the Wellz file can be accessed later at this “Wellz Start Up” dialogue box using the Open button.

5-1


Step 3: Enter the required Header data From the Proposal front

Label for graph. Example: Actual Leg #1 Vs Proposed Leg #1

Enter the V-section that the proposal is calculated on. From Proposal middle pages.

Enter the actual KB elevation of the rig. Enter the actual as measured ground elevation for the well site.

When all required fields have been completed, click the OK button to save and close the dialogue box. Clicking the Cancel button will close the dialogue box and not save changes to the header data, leaving the header data blank.

Note: The Header Data can be edited by clicking the Edit Header button on the Survey Tool Bar Tab at the left hand side of the survey screen.

This is the file name that will be printed on the top of the printed survey report. All survey files should be labeled with a “S” ending. ex. 10950S for leg #1 surveys, 10950SA for leg #2 surveys, 10950SB for leg #3 surveys etc. The above survey files will correspond with proposal files 10950P, 10950PA and 10950PB.

5-2


Step 4: Selection of Units (meters vs feet) To work in meters and calculate dogleg severity (DLS) over a 30 m interval, select meters and click Apply. To work in feet and calculate DLS over a 100 foot interval, select feet and click Apply.

Note: The units used for the current Wellz file can be changed later by selecting Units under the Tools drop down box at the top of the main Wellz screen.

Step 5: Saving the file

Ensure that the C drive is selected to save the survey file to your local hard drive.

Click on the create directory button to create a new working directory. Or select an existing directory to save your new Wellz survey file.

Example: My Documents

To save the survey file under the desired directory and file name, click the Save button. To close the “Save As” dialogue box without specifying the file name, click the Cancel button.

Once your working directory has been created (or selected), type the name of the survey file. The name of the survey file should match the file name entered previously in the Set Header Info dialogue box.

Example: 10950S for the build + leg #1 survey file, 10950SA for the leg #2 survey file, 10950SB for the leg #3 survey file and 10950SB1 for a sidetrack off leg #3.

5-3


Step 6: Selecting the Survey

Select the Survey tab to enter the survey section of the Wellz program.

Note: Selecting the Exit tab will also move the user into the survey section of the Wellz ro ram.

5-4


3. SETTING SURVEY VIEW OPTIONS 3.1.

Changing Units

To change the units used for the current Wellz file, select Units under the Tools drop down menu. The Units dialogue box will appear just as it did when you started a new Wellz file.

Note: Changing the units will convert all previously entered survey depth values to the appropriate new measured depth value (ie. 100 feet will change to 30.48 m).

Another method of changing the units used is to single click the green box at the top right corner of the main Wellz survey screen. The Units dialogue box will then appear.

The DLS values may change slightly since the 30 m interval does not exactly match a 100 foot interval.

3.2.

Changing Decimal Places Displayed

Select Set Decimal Places Displayed under the Tools drop down menu. A small dialogue box will then appear.

5-5


3.3.

Arranging Columns

Select Pick Column Arrangement under the Tools drop down menu to pick a new column arrangement. To customize your column arrangement select Create Custom and follow the instructions.

3.4.

Hiding and Unhiding The Survey Tool Bar Tab

To hide the Survey Tool Bar Tab on the left side of the main Wellz survey screen, select ToolBars/Tabs under the Tools drop down menu and click Hide. To view the Survey Tool Bar Tab on the left side of the screen, follow the same steps and click Survey.

The Survey Tool Bar Tab.

5-6


4. INPUTTING SURVEYS

Step 1: Inputting the Tie On Point The first survey station is the Tie On Point. The Tie On Point row will appear in yellow as the active row. Hit the Enter key to input from left to right through the required fields starting with measured depth (MD). The default Tie On Point is all zeros.

Note: Lat = North Dep = East

The Tie On Point can also be edited at any time by double clicking the tie on point row. The “Edit Survey “ dialogue box will then appear.

Step 2: Entering surveys

Once the Tie On Point has been properly entered, click once on the Departure (Dep) field and hit the Enter key to go to the next r ow.

5-7


Input consecutive surveys (MD, INC, AZM) below the Tie On Point as required by hitting the Enter key.

Step 3: Editing The Survey Data

To edit an existing survey station, double click the desired row. Or Single click on the most recent survey station highlighted in yellow. Or Single click the Edit Survey button to enter a row number and access the “Edit Survey” dialogue box.

To delete a survey station from the survey file, click the Delete Row button and input the row number or row numbers that you wish to delete.

Tip: Click on the desired row that you want to delete before clicking

To insert a single survey station, click the Insert Survey button to access the “Insert Survey Point” dialogue box.

the Delete Row button. This will ensure that the row number in the dialogue box corresponds to the row that you want to delete.

5-8


5. INSERTING INTERPOLATED TEXT LINES FOR PRINT The following are the steps required to interpolate surveys with text lines that can be inserted onto your survey printout.

Step 1

To add text to your survey file, select Edit Text Lines under the Tools drop down menu. The Text Lines For Active Well dialogue box will then appear.

Step 2 Insert an interpolated text line by 1: Selecting an Interpolation Method, 2: Entering a Depth, 3: Entering a Text Line and 4: Clicking Add. To edit an existing text line, double click on the desired field in the table at the top of the dialogue box. To delete an existing row, click on the desired row and click the Delete button.

To save your changes and exit the dialogue box, click OK. To save your changes without closing the dialogue box, click Apply.

Note: The interpolated text line survey depths can also be inserted into your survey file by clicking the Apply, Interpolate Text Line Depths to Sheet.

To close the dialogue box without saving your changes, click Close. 5-9


6. QUICK PRINTING Step 1: Access the Quick Print Options Dialogue Box

To print out a listing of the survey file, select Quick Print under the File drop down menu.

Note: The Printer Settings may have to be configured before you are able to print properly.

Step 2: Configure the Quick Print Options Dialogue Box To select the range of survey stations that you wish to print, select Row Number , MD or TVD and the Start and End points.

To include interpolations on the printout, select Interpolate by MD or TVD and click the Apply New Settings button that appears.

Text lines with or without the interpolated Text Line Points can be inserted into the survey print out.

Select to indicate Row Numbers and extrapolated surveys (EXT).

The Start Column and End Column, corresponding to the columns in the main Wellz survey window, can also be selected.

The Quick Print can be Previewed, Printed or Canceled.

5-10


7. TARGETS Step 1: Access the Targets Dialogue Box

To access the targets associated with the current Wellz file, select Show Targets under the Planning drop down menu.

The targets dialogue box can also be accessed by clicking the Targets button on the Survey Tool Bar Tab and clicking Show Targets.

Step 2: Add Targets The location and orientation of multiple targets can be added to the current Wellz file by clicking on the table below. The user has the option of inputting the Latitude (north) and Departure (east) OR the Closure distance and Closure Azimuth from surface for each target. A target radius can be specified in the Targets dialogue box.

Note: The target will not appear on the plan view graphics unless the Graph Target Points is turned on. To add more targets, expand the size of the above table by clicking the Add Target bu tton.

To delete a target, click the Delete Target button and enter the appropriate row number.

To do this, select Options under the Graphics drop down menu and check the Graph Target Points. 5-11


8. PROJECTING TO BIT Step 1: Open Project To Bit dialogue box

To access the Project To Bit dialogue box, select Project To Bit under the Survey drop down menu.

The Project To Bit dialogue box can also be access using the Project To Bit button on the Survey Tool Bar Tab.

Step 2: Set Parameters For Projection To Bit These are the survey numbers to the last survey station.

Once the Build Rate, Turn Rate and Change in MD have been entered, click Calculate. The projected survey to the bit will appear in the adjacent row.

Input the estimated Build Rate, Turn Rate to a specific measured depth distance ahead (Change in MD).

Note: When projecting to the bit, the Change in MD distance is the distance from the bit to the survey tool sensor.

If you wish, the projection to bit survey can be inserted into the survey file by clicking the Insert in Active Well button. Note: The inserted survey will have an EXT row number and all row numbers thereafter will be EXT extension. To remove the EXT rows, use the Delete button.

5-12


9. PROJECTING AHEAD 9.1.

Projecting To A Target

Step 1: Open Project Ahead Dialogue Box To access the Project Ahead dialogue box, select Project Ahead under the Survey drop down menu.

The Project Ahead dialogue box can also be accessed using the Project Ahead button on the Survey Tool Bar Tab.

5-13


Step 2: Set Parameters For Projecting To a Target

The target for the projection can be selected by entering the target row number or by clicking the Get Next Target or Get Previous Target buttons.

The survey station that the projection is tied to can be selected by entering the survey row number or by clicking the Get Next Survey or Get Previous Survey buttons.

The Straight Line Projections from the selected survey station to the selected target are displayed above. This projection method indicates to the directional driller whether the well is lined up to hit inside or outside the target radius.

Note: Remember to enter a target radius for the selected target.

The Build Rate To Target TVD and Target Inc is displayed below.

Note: This is NOT the build rate to target. Note: For this number to be meaningful, the desired target inclination and target TVD must be entered in the Target info (Edit Targets).

The Required Correction To Targets, calculated from the selected survey station to the selected target, are displayed above. The required correction uses a constant dogleg to target projection method.

To create extrapolations using various projection methods, click the Project Ahead button.

To edit or add a target to the list, click the Edit Targets button below (right).

5-14


9.2.

Projecting Ahead (Extrapolating)

Step 1: Set Parameters For Projecting Ahead

Select from one of the seven Projection Methods below.

Once a Projection Method has been selected, the appropriate variables will appear below. To adjust the parameter values, click on a box and enter a new value Click Calculate after all variables are entered to update the extrapolation in the table bel ow.

Parameter Values can also be adjusted by clicking the Step Buttons below. This input method will calculate automaticall y

Note: The size of each step can be changed by checking the Set Step Sizes Mode box.

Note: When a Projection Method is selected, the default parameter values that appear are linked to the corresponding selected target values. To change the target, select the Next Target or Previous Target buttons. Following the last survey station, the Extrapolation (EXT) will appear in the above table. Each time the Projection Method and/or parameter values change, the EXT row will change accordingly.

To extrapolate from an extrapolation, click the Post Projection button and select another Projection Method.

To delete the last extrapolation, click the Delete Projection button.

To add the extrapolation(s) to the survey file, click the Ok (add to surveys) button. The extrapolation(s) will appear in the survey file with EXT row numbers. To close this dialogue box without adding the extrapolation(s) to the survey file, click the Close button.

Note: The extrapolated survey station(s) can be removed from the survey file l ater by following the same steps to remove an actual survey station (row). 5-15


10. INTERPOLATING 10.1. Inserting a Single Interpolated Point The following steps will allow the user to insert a single interpolated point. The interpolated point will appear as an actual survey station in the Well z file.

Step 1: Select an Interpolation Method Insert an interpolated point by clicking Insert Interpolated Point under the Tools drop down menu. Select one of the interpolation options (Measured Depth, TVD or Subsea). A dialogue box will then appear where you can enter the desired interpolation depth.

After an interpolated depth has been entered, the Show Interpolation dialogue box will then appear. To insert the interpolated point as a survey row, click the Insert in Active Well button. To close the dialogue box without inserting the interpolation, click the Close button.

Note: To remove the inserted interpolated point, follow the same steps used to remove an actual survey station (row). The current version of wells does not distinguish interpolated survey stations with actual survey stations. To indicate that a survey station is an interpolation, insert a text line at the same interpolated depth following the steps outlined in Section 5. The text line should clearly state that the survey station is an interpolation. Ex. “INTERPOLATION”.

5-16


10.2. Viewing and Printing Multiple Interpolations To create multiple interpolations across the entire survey file that can only be Viewed or Printed, follow the steps outlined below.

1. Select Show Plan Survey under the Planning drop down menu. 2. Select Interpolate by Measured Depth or Interpolate by TVD that the distance will be calculated on. 3. Enter the desired interpolated distance.

Note: To remove (hide) the interpolated points follow the same steps above and select Hide Interpolated points.

Note: The multiple interpolated points do not become survey stations and can only be viewed or printed.

5-17


11. GRAPHICS 11.1. The Graphics Menu The Graphics Menu allows the user to change the look of the Graphics Window.

When multiple Wellz files are open in memory, each file can be turned OFF or ON using the Pick Wells to Display.

To open a graphics window, selected the desired view (3-d, Plan or Section). To close the graphics window, select Hide Graphics.

To modify the view of the graphics window relative to the Active Well, select from the list.

Select Options to further modify the graphics window. (Section 11.3)

Use this option when viewing the 3-d View. A dialogue box will appear requesting the number of frames for 360 degrees of rotation. Enter a suitable value (180) and the 3-d View will rotate

11.2. Plan and Section Views

Step 1: Select the View Select Plan View or Section View under the Graphics drop down box. A Wellz – graphic window will appear on the left side of the screen. A second window will also appear on the right side of the screen containing Graphics Parameters with Well Parameters.

Note: The Well Parameters portion of the screen is a smaller version of the main Survey screen and will not be further discussed in the graphics section of the manual.

5-18


Step 2: Modify The Graphic Parameters PLAN VIEW GRAPHIC PARAMETERS

Scale All

- Decrease the Scale All to zoom in and increase the Scale All to zoom out. The Scale All value affects the east-west and north-south axis together.

Box Center East

- Adjusts the East coordinate of the graphics view (box) center.

Box Center North

- Adjusts the North coordinate of the graphics view (box) center.

Sector Size

- The sector size is the grid box size outlined in black. Increase the sector size to reduce the number of grid lines. Decrease the sector size to increase the number of grid lines.

Scale East

- Decrease the Scale East to expand the east-west axis.

Scale North

- Decrease the Scale North to expand the north-south axis.

Sector East

- The sector size in the East – West direction. - Tip: Match the Sector East value with the Scale East value.

Sector North

- The sector size in the North – South direction. - Tip: Match the Sector North value with the Scale North value.

Note: To view your changes to the graphics window, the Calculate button must be selected.

Note: Using the up and down arrow at the right side of the graphics parameters screen is a quick way to modify the graphics view. The step sizes can be adjusted by checking the Set Step Sizes Mode box. To exit the Set Step Sizes, uncheck the Set Step Sizes Mode box.

5-19


SECTION VIEW GRAPHIC PARAMETERS

Scale All

- Decrease the Scale All to zoom in and increase the Scale All to zoom out. The Scale All value affects the vertical and horizontal axis together.

Box Center TVD

- Adjusts the TVD of the graphics view (box) center.

Section Displacement - Adjusts the Section Displacement of the graphics view (box) center. Sector Size

- The sector size is the grid box size outlined in black. Increase the sector size to reduce the number of grid lines. Decrease the sector size to increase the number of grid lines.

Scale Vertical

- Decrease the Scale Vertical to expand the vertical axis.

Scale Horizontal

- Decrease the Scale Horizontal to expand the horizontal axis.

Sector Vertical

- The sector size in the vertical direction. - Tip: Match the Sector Vertical value with the Scale Vertical value.

Sector Horizontal

- The sector size in the horizontal direction. - Tip: Match the Sector Horizontal value with the Scale Horizontal value.

Note: To view your changes to the graphics window, the Calculate button must be selected.

Note: Using the up and down arrow at the right side of the graphics parameters screen is a quick way to modify the graphics view. The step sizes can be adjusted by checking the Set Step Sizes Mode box. To exit the Set Step Sizes, uncheck the Set Step Sizes Mode box.

5-20


11.3. Graphics Options Select Options under the Graphics drop down menu to access the g raphics options below.

To change the color, thickness and dot line interval for the Active Well, Select the Set Color and Line Type of Well. Red is generally used for the “Proposed” line trajectory and blue is used as the “Actual” line trajectory.

Primarily used to alter only the 3-d view. Also used to change the darkness of the secondary grid lines for all views (ie. Grid Lightener ).

There are three options for adding points to the graph: 1. Graph Survey Points will place a point at every survey station. 2. Graph Points of Interest will graph points from the Points of Interest table. 3. To remove all points from the graph, select Do Not Graph Points.

Select Graph Target Points to display all the targets entered in the Target table on the graph.

Note: Remember to enter a radius for the target in the Target table. The coordinate system used for the graphic view can be selected as: Field Coordinates and Subsea depths OR Local Coordinates and TVD depths

To add, remove or edit the Points of Interest table, select the Edit Points of Interest. To view the points of interest on the graph, select Graph Points of Interest.

Note: The Local Coordinate and TVD system puts the surface location for all Wellz files in memory at a latitude(north) = 0, departure(east) = 0 and KB starts at 0 m TVD. The Local Coordinate system is the most commonly used coordinate system.

Note: The Field Coordinate and Subsea system is based on an arbitrary field center location that all well surface locations can be referenced from. This coordinate system is useful when viewing multiple wells in an area and/or producing anti-collison reports with Wellz. THE FIELD COORDINATE SYSTEM SHOULD ONLY BE USED WHEN THE NORTH OF FIELD CENTER, EAST OF FIELD CENTER AND KB ELEVATION VALUES FOR ALL WELLZ FILES IN MEMORY ARE PROPERLY ENTERED IN THE EDIT HEADER DATA DIALOGUE BOX. 5-21


LWD SENSOR THEORY, APPLICATION, & INTERPRETATION

Directional Data

Importance of Directional Data

“Delivery of high quality, accurate directional data is your highest priority on my wellsite” - the customer

Importance of Directional Data

• Things to remember: – You only have one chance to put the hole in the right spot – You can’t assume that because the computer comes up with an answer that it’s always correct (GIGO) – It costs the company lots of money (profit) to correct a directional data screw up

Implications of Bad Directional Data

• Well is drilled at wrong inclination or in wrong direction • Well collides with another well • Well crosses a lease line • We lose credibility with the customer • You potentially lose your job

What is Survey Data? • A survey, or more appropriately a survey station, consists of the following components: – Inclination – Hole Direction (Azimuth) – Measured Depth

• The highest quality survey data is best achieved as a static measurement • Survey data tells the directional driller where the hole has been • Inclination and hole direction are downhole directional sensor measurements • Measured depth is a surface derived depth monitoring system measurement

Inclination • Inclination is the angle, measured in degrees, by which the wellbore or survey instrument axis varies from a true vertical line • An inclination of 0° would be true vertical • An inclination of 90° would be horizontal.

Hole Direction • Hole direction is the angle, measured in degrees, of the horizontal component of the borehole or survey instrument axis from a known north reference • This reference is true north or grid north, and is measured clockwise by convention • Hole direction is measured in degrees and expressed in either azimuth form (0° to 360°) or quadrant form (NE, SE, NW, SW)

Measured Depth • Measured depth refers

to the actual depth of hole drilled measured from the surface location (drill floor) to any point along the wellbore

What is Steering Data? • Steering, or toolface data, is dynamic data and tells the directional driller the position of the bend of the mud motor • Orienting the bend to the desired position allows him to control where the hole will be going • There are two types of toolface data – Magnetic – Highside (Gravity)

Magnetic Toolface • Magnetic toolface is the direction, in the horizontal plane, that the mud motor bend is pointing relative to the north reference

• Magnetic Toolface = Dir Probe Mag Toolface + Total Correction + Toolface Offset • Magnetic toolface is typically used when the inclination of the wellbore is less than 5° • The magnetic toolface reading is whatever magnetic direction the toolface is pointed to

Gravity Toolface • Gravity toolface is the angular distance the mud motor scribeline is turned, about the tool axis, relative to the high side of the hole • Gravity toolface = Dir Probe Gravity Toolface + Toolface Offset • If the inclination of the wellbore is above 5°, then gravity toolface can be used • The toolface will be referenced to the highside of the survey instrument, no matter what the hole direction of the survey instrument is at the time • The toolface will be presented in a number of degrees either right or left of the highside

Gravity Toolface • For example, a toolface pointed to the highside of the survey instrument would have a gravity toolface of 0° • A toolface pointed to the low side of the survey instrument would have a gravity toolface of 180° • If the probe highside point was rotated to the right of highside, the gravity toolface would be 70° to the right.

Electronic Accelerometer & Magnetometer Axes • “Z” axis is along the length of the probe (axial plane) • “X” and “Y” are in the cross-axial plane and are perpendicular to each other and to the “Z” axis • “Highside” is aligned with the “X” axis • All three axes are “orthogonal” to each other

Quartz-Hinge Accelerometers • Respond to the effect of the earth’s gravitational field in each plane • An alternating current (AC) is used to keep the quartz proof mass in the reference position as the accelerometer is moved relative to gravity • The intensity of the “bucking” current is related to the gravitational force felt by the accelerometer

Fluxgate Magnetometers • •

•

•

•

Respond to the effect of the earth’s magnetic field in each plane The magnetometer contains two oppositely wound coils around two highly magnetically permeable rods As AC current is applied to the coils, an alternating magnetic field is created, which magnetizes the rods Any external magnetic field parallel with the coil will cause one of the coils to become saturated quicker than the other The difference in saturation time represents the external field strength.

Earth’s Magnetic Field •

The outer core of the earth contains iron, nickel and cobalt and is ferromagnetic • The Earth can be imagined as having a large bar magnet at its center, lying (almost) along the north-south spin axis • Although the direction of the field is magnetic north, the magnitude will be parallel to the surface of the Earth at the equator and point steeply into the Earth closer to the north pole

Earth’s Magnetic Components • • • • • • •

•

M = Magnetic North direction N = True North direction Btotal = Total field strength of the local magnetic field Bv = Vertical component of the local magnetic field Bh = Horizontal component of the local magnetic field Dip = Dip angle of the local magnetic field in relationship to horizontal Dec = Variation between the local magnetic field’s horizontal component and true north Gtotal = Total field strength of the Earth’s gravitational field

Dip Angle vs. Latitude • Lines of magnetic flux lie perpendicular (90°) to the earth’s surface at the magnetic poles • Lines of magnetic flux lie parallel (0°) to the earth’s surface at the magnetic equator • Dip Angle increases as Latitude increases • As dip angle increases the intensity of the horizontal component of the earth’s magnetic field decreases

Dip Angle vs. Latitude • At the magnetic equator, Bh = Btotal, Bv = 0

• At the magnetic poles, Bh = 0, Bv = Btotal • Bh is the projection (using the dip angle) of Btotal into the horizontal plane

Bh = Btotal

Bv = Btotal Bh = 0

Bh = Btotal(cos Dip)

Btotal Bv = Btotal(sin Dip)

Magnetic Declination •

Complex fluid motion in the outer core causes the earth’s magnetic field to change slowly and unpredictably with time (secular variation) • The position of the magnetic poles also change with time • However, we are able to compensate for this variability by applying a correction (declination) to a magnetic survey which references it to true north

Magnetic Pole Movement (1945 – 2000) North Pole

South Pole

True North • True north, or geographic north, is aligned with the spin axis of the Earth • True north does not move making it a perfect reference • A survey referenced to true north will be valid today and at any time in the future • The correction we apply to change a magnetic north direction to a true north direction is called declination.

Applying Declination • To convert from Magnetic North to True North, Declination must be added: True Direction = Magnetic Direction + Declination Important Note: •

East Declination is Positive & West Declination is Negative in both the northern and southern hemispheres

Applying an East Declination • An east declination means that magnetic north is east of true north • For example, if magnetic north hole direction is 75° and the declination is 5° east, the true north direction would be calculated as follows: True Direction = Magnetic Direction + Declination 80° = 75° + (+5°)

Applying a West Declination • A west declination means that magnetic north is west of true north • For example, if magnetic north hole direction is 120° and the declination is 5° west, the true north direction would be calculated as follows: True Direction = Magnetic Direction + Declination 115° = 120° + (-5°)

Implications of an Incorrect Declination • Since declination is a addition of degrees of correction to the magnetic hole direction, any mistakes made to the declination have serious consequences. • For example, if you intend to apply a +18° declination but instead input a -18 ° declination, your reported hole direction will be wrong by 36°! • This mistake may not be detected until the data is compared against independent survey data

Grid Convergence • Corrects for the distortion caused by projecting the curved surface of the earth onto a flat plane • Correction becomes more severe moving from the equator towards the poles • Two common projection methods are Transverse Mercator and Lambert

UTM Grid Projection • In the Universal Transverse Mercator Grid, the earth is divided into sixty, 6° grid zones

Grid Zones • A central meridian bisects each 6° grid zone • Each central meridian is along true north • If directly on the central meridian or on the equator, the grid correction is ZERO

Convergence is zero here

Grid Zones • Convergence correction increases as location moves away from the equator and central meridian • Convergence should not be more than +/-3°, otherwise the incorrect central meridian has been chosen

Maximum Grid Correction

Grid Zones • For rectangular coordinates, arbitrary values have been established within each grid

Comparing Grid Projections • Different projections yield varying views in terms of distance, shape, scale, and area

Applying Convergence • To convert from Grid North to True North, Convergence must be subtracted: Grid Direction = True Direction – Convergence Important Note: •

East Convergence is Positive & West Convergence is Negative in the Northern Hemisphere

•

East Convergence is Negative & West Convergence is Positive in the Southern Hemisphere

Applying an East Convergence • An east convergence means that grid north is east of true north • For example, if true north hole direction is 70° and the convergence is 3° east, the grid north direction would be calculated as follows:

Grid Direction = True Direction - Convergence 67° = 70° - (+3°)

Applying a West Convergence • A west convergence means that grid north is west of true north • For example, if true north hole direction is 120° and the convergence is 3° west, the grid north direction would be calculated as follows:

Grid Direction = True Direction - Convergence 123° = 120° - (-3°)

Applying Declination and Convergence Simultaneously • Replacing the formula for a true north direction in the grid north direction equation gives us the following formula: • Grid Direction = Magnetic Direction + Declination – Convergence • (Declination – Convergence) is called the Total Correction

• If magnetic declination is 5° east and the grid convergence is 3° west, and the magnetic direction is 130°, the grid direction is calculated as: 138° = 130° + (+5°) - (-3°)

Static Survey Procedure • Drill down to the end of the joint or stand and stop rotating • Work the pipe up and down to release any built up torque in the drillstring • Lower the bit to the survey point and shut down the pumps • Wait 30 – 40 seconds • Turn on the pumps and transmit the survey to the surface (pipe may be moved slowly while sending up the survey)

Sources of Real-time Inclination Errors • These factors can introduce error into the inclination value presented to the directional driller: – Movement during a survey (axial or rotational) – Accelerometer or associated electronics failure – Calibration out of specifications – Sensor measurement accuracy – Real-time Data resolution

Inclination Quality Checks • Does the inclination value match the actions of the directional driller? • Is Gtotal within +/- 0.003 g of the Local Gravitational Field Strength? 2

2

2

Gtotal = (Gx + Gy +Gz )

1/2

Sources of Real-time Azimuth Errors • These factors can introduce error into the hole direction value presented to the directional driller: – Magnetic Interference (axial or cross-axial) – Magnetometer or associated hardware failure – Calibration out of specification – “Bad” accelerometer input (inclination and highside toolface are part of the calculation!) – Mathematical Error (at 0° and 90° inclination) – Sensor measurement accuracy – Real-time Data resolution – Latitude, Inclination, Hole direction – Wrong Declination and/or Convergence

Azimuth Quality Checks • Does the azimuth value match the actions of the directional driller? • Is Btotal within +/- 350 nT of the Local Magnetic Field Strength? 2

2

2

Btotal = (Bx + By +Bz )

½

• Is Gtotal within +/- 0.003 g of the Local Gravitational Field Strength?

Additional Survey Quality Checks (Bx * Gx) + (By * Gy) + (Bz * Gz) • MDIP = ASIN {----------------------------------------------} Gtotal * Btotal •

Is the calculated Magnetic Dip value within +/- 0.3º of the Local Magnetic Dip value?

•

MDIP utilizes inputs from the accelerometers and magnetometers but is not as sensitive of a quality check as Gtotal and Btotal

•

It is possible for the MDIP to be out of specification even if the Gtotal and Btotal are not

•

NOTE: MDIP should not be used as sole criteria to disqualify a survey if Gtotal and Btotal are within specification

Survey Quality Checks 2

2

2

2

2

• Gtotal = (Gx + Gy +Gz ) 2

• Btotal = (Bx + By +Bz )

1/2

1/2

(Bx * Gx) + (By * Gy) + (Bz * Gz) • MDIP = ASIN {----------------------------------------------} Gtotal * Btotal

Survey Quality Check Limits

• Gtotal = Local Gravity +/- 0.003 g • Btotal = Local Field +/- 350 nT • MDIP = Local Dip +/- 0.3°

Survey Quality Example #1 Given the following survey data, decide whether each quality check is within limits Local References:

INC 3.72

Gtotal = 1.000 g

AZ 125.01

Btotal = 58355 nT

Gtotal 1.0012

Mdip = 75.20

Btotal MDip 58236 75.25

Based on your observations, are the inclination and azimuth values acceptable?


INC 3.72

Gtotal = 1.000 g

AZ 125.01

Btotal = 58355 nT

Gtotal 1.0012 +0.0012

Mdip = 75.20

Btotal MDip 58236 75.25 -119 -0.05

Based on your observations, are the inclination and azimuth values acceptable? YES / YES


INC 5.01

Gtotal = 1.000 g

AZ 127.33

Btotal = 58355 nT

Gtotal 1.0009

Mdip = 75.20




INC 5.01

Gtotal = 1.000 g

AZ 127.33

Btotal = 58355 nT

Gtotal 1.0009 +0.0009

Mdip = 75.20

Btotal MDip 58001 74.84 -354 -0.36

Based on your observations, are the inclination and azimuth values acceptable? YES / NO


INC 8.52

Gtotal = 1.000 g

AZ 125.34

Btotal = 58355 nT

Gtotal 0.9953

Mdip = 75.20




INC 8.52

Gtotal = 1.000 g

AZ 125.34

Btotal = 58355 nT

Gtotal 0.9953 -0.0047

Mdip = 75.20

Btotal MDip 58150 74.28 -205 -0.92

Based on your observations, are the inclination and azimuth values acceptable? NO / NO


INC 17.13

Gtotal = 1.000 g

AZ 129.88

Btotal = 58355 nT

Gtotal 1.0120

Mdip = 75.20




INC 17.13

Gtotal = 1.000 g

AZ 129.88

Btotal = 58355 nT

Gtotal 1.0120 +0.0120

Mdip = 75.20

Btotal MDip 57623 73.44 -732 -1.76

Based on your observations, are the inclination and azimuth values acceptable? NO / NO

Survey Calculation Methods • Once we have verified the quality of the inclination, hole direction, and measured depth values at the survey station the data is then passed to the directional driller • Survey calculations are performed between survey stations to provide the directional driller with a picture of the wellbore in both the vertical and horizontal planes • If the input parameters are identical the calculated survey values on your survey report should match the directional drillers’

Survey Calculation Methods • Survey calculations are more easily understood by applying basic trigonometric principles

Tangential Calculation Method • Assumes that the borehole is a straight line from the first survey to the last

Average Angle Calculation Method • Assumes distances from survey to survey are straight lines • Fairly accurate and conducive to hand calculations

Radius of Curvature Calculation Method • Applies a “best fit” curve (fixed radius) between survey stations • More accurately reflects the shape of the borehole than Average Angle

Minimum Curvature Calculations • Uses multiple points between survey stations to better reflect the shape of the borehole • Slightly more accurate than the Radius of Curvature method

Comparison of Calculation Methods

• Total Survey Depth @ 5,985 feet • Maximum Angle @ 26° • Vertical hole to 4,064 feet, then build to 26° at 5,985 feet • Survey Intervals approximately 62 feet

Survey Terminology

Survey Terminology • Survey Station – Position along the borehole where directional measurements are taken

• True Vertical Depth (TVD) – The projection of the borehole into the vertical plane

• Measured Depth (MD) – The actual distance traveled along the borehole

• Course Length (CL) – The measured distance traveled between survey stations

Survey Terminology •

Horizontal Displacement (HD) – Projection of the wellbore into the horizontal plane – Horizontal distance from the wellhead to the last survey station – Also called Closure

•

Latitude (Northing) – The distance traveled in the northsouth direction in the horizontal plane – North is positive, South is negative

•

Departure (Easting) – The distance traveled in the eastwest direction in the horizontal plane – East is positive, West is negative

Survey Terminology •

Target Direction – The proposed direction of wellbore

•

Vertical Section (VS) – The projection of the horizontal displacement along the target direction – The horizontal distance traveled from the wellhead to the target along the target direction

•

Dogleg Severity (DLS) – a normalized estimate (e.g., degrees / 100 feet) of the overall curvature of an actual well path between two consecutive survey stations

Vertical Section Calculation •

To cal calculate ate vertical section the closure (horizontal displacement), closure direction, and target direction must be known

•

The vertical section is the product of the horizontal displacement and the difference between the closure direction and target direction

VS = HD * (Target (Target Direction Direction – Closure Closure Direction) Direction)

Vertical Projection •

•

In the vertical projection the directional driller plots True Vertical Depth versus Vertical Section The wellbore must pass through the vertical target thickness along the vertical section direction in order to hit the target in this plane

Kickoff Point True Vertical Depth

Build Section Locked in Section

Tangent Vertical Section

Horizontal Projection •

•

In the horizontal projection the directional driller plots Latitude versus Departure The wellbore must pass through the horizontal target radius along the proposed target direction in order to hit the target in this plane

N

Closure

Proposal Direction

Latitude

E Departure

Vertical Section

Introduction to Directional Drilling

• Directional drilling is defined as the practice of controlling the direction and deviation of a well bore to a predetermined underground target or location

1

Directional Wells

• Slant • Build and Hold • S-Curve • Extended Reach • Horizontal

2

Applications of Directional Drilling

• Multiple wells from offshore structure • Controlling vertical wells • Relief wells

3


• S-Curve

4


• Extended-Reach Drilling • Replace subsea wells and tap offshore reservoirs from fewer platforms • Develop near shore fields from onshore, and • Reduce environmental impact by developing fields from pads

5

Directional Drilling Tools

• Steerable motors • Instrumented motors for geosteering applications • Drilling tools • Surveying/orientation services • Surface logging systems • At-bit inclination 6


• Sidetracking

• Inaccessible locations

7


8


• Drilling underbalanced

• Minimizes skin damage, • Reduces lost circulation and stuck pipe incidents, • Increases ROP while extending bit life, and • Reduces or eliminates the need for costly stimulation programs.

9

Directional Drilling Limitations

• Doglegs • Reactive Torque • Drag • Hydraulics • Hole Cleaning • Weight on Bit • Wellbore Stability 10

Methods of Deflecting a Wellbore

• Whipstock operations • Still used

• Jetting • Rarely used today, still valid and inexpensive

• Downhole motors • Most commonly used, fast and accurate

11

Whipstock Operations

12

Jetting

13

Effect of Increased Bit Weight

• Increase Weight on Bit – Increase Build Rate

14

Effect of Decreased Bit Weight

• Decrease Inclination Decrease Weight on Bit

15

Reasons for Using Stabilizers

16

•

Placement / Gauge of stabilizers control directional

•

Stabilizers help concentrate weight on bit

•

Stabilizers minimize bending and vibrations

•

Stabilizers reduce drilling torque less collar contact

•

Stabilizers help prevent differential sticking and key seating

Stabilization Principle • Stabilizers are placed at specified points to control the drill string and to minimize downhole deviation • The increased stiffness on the BHA from the added stabilizers keep the drill string from bending or bowing and force the bit to drill straight ahead • The packed hole assembly is used to maintain angle

17

Stabilizer Forces

18

Design Principles

• Side force • Fulcrum Principle • Weight on Bit

19

Typical Side Force vs. Inclination

20

Side Force

• Force resulting from bending the tubular • F S = Bi * SC * 3.0 LT3 • Bi : displacement distance of bending interference, in • SC : stiffness coefficient, lb in 2 • LT : axial length over which bend occurs, in 21

Typical Collar Stiffness

• SC = IE • I: moment of inertia, in4 • E: modulus of elasticity • SC : stiffness coefficient, lb in 2 4

4

I = π/64 (DO - Di )

22

Properties of Tubular Steels Metal

Density lb/ft

3

6

Modulus of elasticity 10 psi

Low Carbon Steel

491

29.0

Cr-Mo Steel

491

28.0

Monel K-500

529

26.0

304 Stainless

501

27.4

316 Stainless

501

28.1

Inconel

526

31.0

Aluminum

170

10.3

23

Physical Properties

• Modulus of elasticity • Size and weight • Stiffness

24

Drill Collar Weight

25

Fulcrum Principle • Fulcrum-stabilizer inserted drill string above the bit • Applied weight causes the bottom collars to bow o

• Above 5 inclination, it bows toward the low side of the hole • Pushes the bit hard against the top of the hole, build section

26

Build Assemblies

• Building assemblies use a fulcrum to create and control positive side force F1 L1 = F2 L2

27

Fulcrum Position

• The closer to the bit the higher the side force for given drill collar size

28

Weight on Bit

• Axial loading created by weight on bit produces buckling forces between stabilizer and bit • Hole size • Collar size • Weight on bit

29

Directional Control

• BHA types

• Design principles

• Drop (pendulum)

• Side force

• Build (fulcrum)

• Bit tilt

• Hold (packed hole)

• Hydraulics • Combination

30

Pendulum Principle

• The stabilizer above the bit is removed and an additional drill collar is added, making the bottom hole assembly more flexible • The upper stabilizers, properly placed, hold the bottom drill collar away from the low side of the hole • Gravitational forces act on the bottom collar and bit, causing the hole to lose or decrease angle 31

Dropping Assemblies

• Dropping assemblies act as a pendulum to create and control negative side force

32

Slick Assembly

• To increase drop rate: • increase stiffness • increase bit size to collar size ratio • increase drill collar weight • decrease weight on bit • increase rotary speed

33

Stabilizer Placement

• To increase drop rate: • increase tangency length • increase stiffness • increase drill collar weight • decrease weight on bit • increase rotary speed

34

Dropping Assemblies • To increase drop rate: • • • • •

increase tangency length increase stiffness increase drill collar weight decrease weight on bit increase rotary speed

• Common TL: • • • •

30 ft 45 ft 60 ft 90 ft

35

Drop Assemblies Response

High Medium Low -

36

Angle Drop 90' •

Inclination • 30° - 45°

WOB Est. drop rate/100 ft 0 - 15,000 lbs 2.00° - 2.50° 15,000 - 30,000 lbs 1.25° - 1.50°

• 20° - 30°

0 - 15,000 lbs 15,000 - 30,000 lbs

1.25° - 1.50° 0.75° - 1.00°

•

5° - 20°

0 - 15,000 lbs 15,000 - 30,000 lbs

0.75° - 1.00° 0.50° - 0.75°

•

0° - 5°

0 - 15,000 lbs 15,000 - 30,000 lbs

0.00° - 0.50° 0.00° - 0.00°

37

Angle Drop 60' •

Inclination

• 30° - 45°

• 20° - 30°

•

38

0° - 20°

WOB

Est. drop rate/100 ft

0 - 15,000 lbs

1.25°

15,000 - 30,000 lbs

1.00°

0 - 15,000 lbs

1.00°

15,000 - 30,000 lbs

0.75°

0 - 15,000 lbs

0.75°

15,000 - 30,000 lbs

0.50°

Angle Drop 30' •

Inclination

• 20° - 45°

• 20° - 30°

WOB

Est. drop rate/100 ft

0 - 15,000 lbs

0.75°

15,000 - 30,000 lbs

0.50°

0 - 15,000 lbs

0.25°

15,000 - 30,000 lbs

0.25°

39

Building Assemblies

• Two stabilizer assemblies increase control of side force and alleviate other problems

40

Build Assemblies Response

High High High Medium Medium Medium Low -

41

Hold Assemblies Response

High High High Medium Low 42

Expected Dog Leg BR = θ x 200

BR = θ x 60

L1 + L2 English units

L1 + L2 SI units

43

Predicting Build Rate BR = delta Inc. x 30 Curve length

44

Special BHA’s

• Tandem Stabilizers • Provides greater directional control • Could be trouble in high doglegs

• Roller Reamers • Help keep gauged holes in hard formations • Tendency to drop angle

45

Application of Steerable Assemblies

• Straight-Hole • Directional Drilling / Sidetracking • Horizontal Drilling • Re-entry Wells • Underbalanced Wells / Air Drilling • River Crossings

46

Steerable Assemblies

• Build • Drop • Hold

47

48

Planning a Directional Well • Geology • Completion and Production • Drilling Constraints

49

Geology • Lithology being drilled through • Geological structures that will be drilled • Type of target the geologist is expecting • Location of water or gas top • Type of Well

50

Completion and Production

• Type of completion required (“frac job”, pumps and rods, etc.) • Enhanced recovery completion requirements • Wellbore positioning requirements for future drainage/production plans • Downhole temperature and pressure

51

Drilling

• Selection of surface location and well layout • Previous area drilling knowledge and identifies particular problematic areas

52

Drilling

• Casing size and depths • Hole size • Required drilling fluid • Drilling rig equipment and capability • Length of time directional services are utilized • Influences the type of survey equipment and wellpath

53

Planning • Build rates • Build and hold profiles should be at least 50m • Drop rate for S-curve wells is preferably planned at 1.5 o/30m • KOP as deep as possible to reduce costs and rod/casing wear • In build sections of horizontal wells, plan a soft landing section

54

Planning

• Avoid high inclinations through severely faulted, dipping or sloughing formations • On horizontal wells clearly identify gas/water contact points • Turn rates in lateral sections of horizontal • Verify motor build rates

55

Planning • Where possible start a sidetrack at least 20m out of casing • Dogleg severity could approach 14o/30m coming off a whipstock • Identify all wells within 30m of proposed well path and conduct anticollision check

56

• The cuttings are effectively suspended by the fluid shear and beds do not form for holes inclined less than 30°. • Beyond 30°, the cuttings form beds on the low side of the hole which can slide back down the well, causing the annulus to pack-off. • These cuttings can be transported out of the well by a combination of two different mechanisms. • Slide as a block • transported at the bed/mud interface as ripples or dunes

57

Hole Cleaning

58

Hole Cleaning

Cuttings removal generally becomes more difficult as hole angle increases. Angles between 50°–60° present most problems because the cuttings have a tendency to slide down the annulus and cause packing off. In wells deviated beyond 60°, the cuttings form stable beds. These beds are supported by the sliding friction against the wellbore. The angle range for cuttings bed slide depends largely on mud rheology and problems cleaning the hole can be experienced from 40°–60°. 59

Hole Cleaning

Increases in penetration rate result in higher cuttings concentrations in the annulus. Past experience has shown that 0.5% is the maximum allowable annular concentration to efficiently drill vertical and near vertical wells. For deviated wells, deeper cuttings beds form as the penetration rate increases. Removing these deeper beds require higher flowrates. It is important to control and limit instantaneous ROP’s in deviated wells since deep beds are difficult to remove. PERCENT (%) 60

Hole Cleaning

• Low viscosity fluids are most effective at angles above 30° since they induce turbulence and encourage cuttings removal by saltation. • Plastic viscosity should be minimized to reduce pressure losses and obtain a flatter viscosity profile.

61

Hole Cleaning

The single most crucial factor for successful hole cleaning is mud flow rate, especially for deviated holes. As a rough guide, the annular velocity needed for cleaning wells deviated 50°–60° is approximately twice that required for the vertical case. Take all reasonable steps to reduce frictional pressure. Doing so will extend the range of available flowrate. In critical cases, careful consideration should be given to BHA design, nozzle selection, and additional losses due to mud motors/MWD tools. 62

Hole Cleaning

• If sufficient flow rate is available for hole cleaning, then bit nozzles can be selected for optimum hydraulics in the normal way. When sizing bit nozzles, it is also important to note that: • Certain mud motors have optimum bit differential pressure ranges • Nozzles should be selected to minimize potential hole erosion problems for friable formations

63

Hole Cleaning

• Turbulent/transitional flow is most effective in cleaning and evacuating/minimizing cuttings bed formation • Laminar flow • highest possible pump output/annular velocities. • Optimize the low shear rheology • High initial gel strength gives rapid suspension of cuttings • wiper trips, pipe rotation, reciprocation, backreaming when top drive is available, and pills pumped 64

Hole Cleaning

Mud weight influences hole cleaning by affecting the buoyancy of the drilled cuttings. This applies for both vertical and deviated holes. For small changes in density, the flowrate required to maintain adequate hole cleaning is directly proportional to the cuttings mud density differential.

65

Hole Cleaning

Increased cuttings density make hole cleaning more difficult for both vertical and inclined wells. Cuttings shape and size is also important in vertical transport. The larger, more rounded particles are the hardest to remove. Shape and size have little influence in highly deviated wells because the cuttings move in blocks rather than discrete particles.

66

Hole Cleaning Rotating the drillstring will assist in mechanically disturbing cuttings beds in deviated wells. The rotating pipe forces cuttings upwards to the high side of the hole, and into the fast moving mud stream. Drillpipe rotation also encourages mud flow in the narrow gap between the pipe and the settled bed. When a downhole motor in oriented mode is used in a deviated well, the cuttings beds are probably not being disturbed. Consider rotating the string prior to tripping. Field studies show that pipe rotation while drilling enhances the hole cleaning efficiency. 67

• • • •

• • •

68

Flow rates in the 300–500 gpm range will generally be adequate for cleaning 216 mm (8-1/2 in) horizontal sections. Select mud properties which provide turbulent flow, if possible. 2 To achieve turbulence, maintain maximum mud YP close to 10 lb/100 ft . ECD increases when drilling horizontally, but formation strength remains fixed. Ensure that ECD does not cause formation breakdown when drilling horizontal section. Select MWD/downhole motors that do not restrict flow rates for hole cleaning. Limiting nozzle pressure drop for motor considerations (i.e., maximum allowable bit pressure drop for motor being used) may be necessary. If possible, plan well trajectory to avoid drilling long sections of large diameter holes above 50°. Look closely at the pump capacity of the rig.

Hole Cleaning Drilling Hydraulics

• • • • • • • • • •

Deviated wells require higher flow rates. Design BHA’s for minimum pressure loss in critical wells. Hole angles 50°–60° are most difficult to clean (can be 45°–60° dependent on mud rheology). Control instantaneous ROP’s. Increase flowrate rather than changing rheology when cleaning deviated wells. Increased mud weight assists cuttings removal. Drillpipe rotation assists hole cleaning in deviated holes. A minimum of 60 rpm is recommended. Higher rpm’s assist. Minimize hole washouts by developing a good hydraulic design. Drill “minimum rat hole” consistent with safe running of casing. Use a riser booster pump on semi-submersibles, if necessary.

69

• Always circulate the hole clean prior to tripping. Use “minimum” circulation times. • Rotate the pipe at maximum of 60 rpm when circulating prior to tripping. • Use low vis/low wt pills for wells > 30°. Calculate volumes to ensure well control. • Make a rotary wiper trip after a long section is drilled with downhole motor. • Make sure cementing pumps are available to pump in the case of an emergency. 70

71

72

Mud Motors

Turbine

PDM

73

Commander TM PDM Motors

74

Motor Selection

• These are the three common motor configurations which provide a broad range of bit speeds and torque outputs required satisfying a multitude of drilling applications • High Speed / Low Torque - 1/2 Lobe • Medium Speed / Medium Torque - 4/5 Lobe • Low Speed / High Torque - 7/8 Lobe

75

Components of PDM Motors

• Dump Subs • Motor Section • Universal Joint Assembly • Adjustable Assembly • Bearing Assembly

76

Dump Sub

• Allows Drill String Filling and Draining • Operation - Pump Off - Open - Pump On - Closed

• Discharged Ports • Connections

77

Motor Section

• Positive Displacement Motor ( PDM ) • Lobe Configurations • Stages

78

Performance Characteristics

Motor Section

• Positive Displacement Motor PDM

79

Universal Joint Assembly • Converts Eccentric Rotor Rotation in to Concentric Rotation • Universal Joint • Flex Rod

Constant Velocity Joint -80

Adjustable Assembly • Two Degree and Three Degree • Field Adjustable in Varying Increments to the Maximum Bend Angle • Used in Conjunction with Universal Joint Assembly H = 1.962

o

81

Bearing Assembly • Transmits bit axial and radial loads to the drillstring • Thrust bearing • Radial bearing • Oil reservoir • Balanced piston • High pressure seal • Bit box connection 82

Motor Specifications

• Motor specifications • Dimensional data • Ultimate load factors • Performance charts

83


84


85

Performance Charts

86

Curso Directional Drilling II log

Recommend Documents