Handout_8

Int nte era ract ctiv ive e Petr trop ophy hysi sics cs LSD Onuigbo Abu-Dhabi, U.A.E. U.A.E. September, 2005

Tool ools s and and Appli Ap plica catio tions ns QuickLo uickLook ok Archie’s Equation Equation Sw = (1/ ) (Rw / Rt ) ½ Hydrocarbon Saturation Resistivity Basics

S W Formatio n Water Water

S W Hydrocarbon

Function of salinity and temperature Infinite Resistivity Dry and non-mettalic m inerals with infinit e resistivity resistivity

Rock Matr Matrix ix

Φ,

Ab u-Dh abi September,, 2005 September 2005

Rt and Rw need to be be determined determined to to compute compute the S w.

2

Tool ools s and and Appli Ap plica catio tions ns Invasion Hydrocarbon Saturation

100% Rmf

Resistivity Basics Borehole Wall

0% Invaded Invade d Tra Transit nsit ion

Annul us

Virgin

The for format mation ion lit lithol hology ogy and Φ do not alter much due to invasion. The Rt chang changes es significan significantly tly in the the invaded invaded zone zone and the the resist resistivity ivity tools need to measure deep into the virgin zone to compute compute the S w. Ab u-Dh abi September,, 2005 September 2005

3

Tool ools s and and Appli Ap plica catio tions ns Rt determination Hydrocarbon Saturation

Deep De ep Log

Medium Me dium Log Very E Shallow L L og O

Depth of Investigation Depth of Re Resistivi sistivity ty Logs

H E R O B

Resistivity Basics

Invaded Zone

Virgin Zone

Rxo = f (V (Very ery Shallow Log Log))

Sxo = 1/

(Rm f /Rxo )1/2

Rt = f (Very Shallow Log,Medium Log,Deep Log)

Sw = 1/

(Rw /Rt )1/2

The resist resistivity ivity tools are are designed designed to read at various various depths depths of investiga investigation. tion. The shallow shallow reading reading is used used to measure measure the S xo. The deep reading is affected by the invasion and is often not the R t. The medium reading, together with the shallow reading, is used to correct the deep reading to obtain the the R t.


4

Tool ools s and and Appli Ap plica catio tions ns

Hydrocarbon Saturation

Rw Determi terminatio nation n from fr om SP Lo Log g K o is dependend dependend on formation temp.

Resistivity Basics

Sta tatic tic SP = - K o log [Rmf e / Rwe ]

Rmfe is equivalent equivalent mud filtrate resistiv resistiv ity Rwe is equivalent water resist ivi ivity ty (S (SPP-2) 2)

The SP can be used us ed to est im imate ate Rw unde underr the following condit ions:

•The SP value remains constant for a minimum of 10 meters •This interval must correspond to clean sandstone •Rmf must remain constant in the same interval


5

Tools and Applications SP-2 Hydrocarbon Saturation Resistivity Basics

Ab u-Dh abi September, 2005

6

Tools and Applications SP-2m

Hydrocarbon Saturation Resistivity Basics


7

Tools and Applications


Rw Determination from Rxo and Rt tools. In clean water bearing formations (S w = 1),

Resistivity Basics

the Archie’s saturation equation becomes: Rw =

2R t

assuming a = 1, m = n = 2


8


Hydrocarbon Saturation Resistivity Basics


9

Tools and Applications Rxo Measurement

Hydrocarbon Saturation Resistivity Micro

The objective of the shallow resistivity tools is to determine the invaded zone resistivity. The tools consist of an arrangement of electrodes on a pad that is pressed against the formation and minimizes borehole effect. Ab u-Dh abi September, 2005

10

Tools and Applications Microlog Device Hydrocarbon Saturation Resistivity Micro

The microlog device consists of two short-spaced devices mounted on the same pad. They provide resistivity measurements for the very small volume of mud-cake and formation immediately adjacent to the borehole. Its limitation is the high sensitivity to mudcake.


11

Tools and Applications Micro-Spherically Focused Log (MSFL)

Hydrocarbon Saturation Resistivity Micro The MSFL device uses additional current electrodes to ensure that a known volume of the formation is measured. The spherical focusing of this tool avoids any variation in the depth of investigation and prevents current loss in the mud-cake. Better Rxo than Microlog. Ab u-Dh abi September, 2005

12

Tools and Applications Micro-Cylindrically Focused Log (MCFL) Hydrocarbon Saturation Resistivity Micro


The PEX MCFL device focuses the current in a cylindrical shape. This design provides for a measurement that is similar in shape to the borehole and mud-cake. Thus, the measurement is insensitive to changes in the borehole geometry and to the environment of the borehole wall. The tool determines Rxo, Rmc and hmc.

13

Tools and Applications Micro-Cylindrically Focused Log (MCFL)



14



Micro-Resistivity Applications

• Rxo measurement in water-based mud • Corrections to deep resistivity tools to determine Rt • Moveable oil determination from Rxo • Qualitative indication of permeability


15



The Schlumberger Chart Rxo-3 provides the mud-cake thickness and resistivity corrections to the MSFL. Ab u-Dh abi September, 2005

16

Tools and Applications Sw Determination Hydrocarbon Saturation Resistivity Micro

For moderate invasion and average residual oil saturation, an empirical relation exists between Sxo and Sw. In the absence of a porosity log, the virgin zone saturation can still be determined. The Sw/Sxo < 0.7 indicates movable oil. Ab u-Dh abi September, 2005

17



Micro-Resistivity Evaluation Techniques Limitations

• Rugose Hole • Oil-based mud • Thick mud cake (MSFL)


18


Hydrocarbon Saturation Resistivity Lateralog


The simple electrical tool theory forms the basis of all electrical tools. The tool has a current source which creates a series of equipotential spheres centered on the source. This configuration will measure the sum of all the resistances between the surface electrode and the downhole electrode. 19

Tools and Applications Focusing Guard Electrode

Hydrocarbon Saturation Resistivity Lateralog The solution is to focus the measure current into the formation. This is done using a current emitted from electrodes above and below the measure electrode. This forces the current to flow in a sheet directly into the formation in front of it with little deviation.

Low resistivity

High resistivity

Low resistivity

High resistivity

Focused current

Low resistivity

Focused System Ab u-Dh abi September, 2005

Bucking current s

Bucking current s

Low resistivity

Non-Focused Syst em 20



LL3

Resistivity Lateralog

Bucking electrode

Passi ve Focusing : equal current is emitted from all three electrodes to focus the current into the formation. But with this arrangement, the equipotential shapes distort very quickly. Bucking electrode


21




Ac tiv e Focusin g : two voltage electrodes (M1 and M2) are introduced between the currentemitting measure electrode and the bucking electrode. They measure the voltage in front of them, an then modulate the measurement (Io) current. This ensures that the voltage in front of them is equal, and thus the are in front of these electrodes is equipotential. So Io flows perpendicular to the tool axis.

22

Tools and Applications Laterolog Tools Various configurations have evolved over the years:


•LL3 - The first focused tool with two bucking electrodes •LL7 - Four extra electrodes added, including a feedback loop to keep the bucking current at an optional value. •LL9 - Two more electrodes added, plus a Shallow Laterolog measurement. Deep and Shallow measurements were taken sequentially. •DLT - Dual Laterolog Tool - same as the LL9 but able to run deep and shallow simultaneously. • ARI - Azimuthal Resistivity Imager - same as DLT with additional capability to measure the resistivity in 12 directions (azimuthal resistivity) around the borehole and acquire higher resolution logs •HALS - Highly Integrated Azimuthal Laterolog - Part of the Platform Express service with similar capability as the ARI.


•HRLA - High Resolution Laterolog Array - Provides resistivity measurement at 6 depths of investigation. 23

Tools and Applications Dual Lateralog Tool Hydrocarbon Saturation Resistivity Lateralog

Deep Bucking Current

Deep Measurement Current


The traditional DLT electrode configuration allows the simultaneous recording of deep (LLD) and shallow (LLS) measurements by operating at two frequencies: 35 Hz for the LLD and 280 Hz for the LLS.

Shallow Bucking Current

Shallow Measurement Current

24

Tools and Applications Dual Lateralog Hydrocarbon Saturation Resistivity Lateralog


Limitation in approach • Does not account for coupling between radial and vertical response Risk of underevaluating reserves • Overestimated Rt in water zones • Underestimated Rt in thin hydrocarbonbearing zones

25

Tools and Applications Azimuthal Resistivity Imager



The ARI uses the same configuration as the DLT to measure the LLD and LLS. It also houses an array of 12 azimuthal electrodes to measure the deep high resolution resistivity around the borehole.

26

Tools and Applications ARI Example Hydrocarbon Saturation Resistivity Lateralog

The azimuthal resistivity imager log consists of the LLD, LLS, LLHR, 12 azimuthal resistivities and 12 electrical stand-off measurements. In addition, image logs of the 12 azimuthal resistivities with the borehole folded open are also presented. Ab u-Dh abi September, 2005

27

Tools and Applications HALS



28



Computed Shallow Focusing

Computed Deep Focusing


MODE 2

MODE 3

Computed shallow focusing

MODE 1

MODE 3

Computed deep focusing

The HALS is a part of the PEX tool string and provides all its benefits. The tool operates in three modes. The linear combinations of a pair of modes is used to obtain the different depths of investigation. Ab u-Dh abi September, 2005

29



HALS Example

The HALS has the same outputs as the ARI. It also provides a shallow resistivity image and the Rm.


30

Tools and Applications HRLA Hydrocarbon Saturation Resistivity Lateralog

The HRLA tool operates in six different modes, producing resistivity measurements at six different depths of investigation. This improves the computation of R t as the invasion effects are well quantified. The tool does not have an azimuthal array. Ab u-Dh abi September, 2005

31

Tools and Applications HRLA Software Solutions Hydrocarbon Saturation Formation Models


• 2D earth model • More accurate Rt computation • Correction for coupling of radial and vertical response • Borehole corrections + Ab u-Dh 1Dabi inversion September, 2005 • 2D and 2D+dip inversion

2D

2.5D 32

Tools and Applications HRLA – Rt from 1D inversion Hydrocarbon Saturation Resistivity Lateralog

• Borehole correction curves and inversion error curves presented on the left track • 1D inversion performed without external Rxo input (MSFL, MCFL), therefore RXO_1D does not correlate to RXO8 due to different depth of investigation. • Resolution of HRLA is comparable to the MCFL resolution • HRLA is the appropriate log to identify invasion profiles Ab u-Dh abi September, 2005

33

Tools and Applications 1D and 2D Inversion Comparison . RLA2 1

Rxo > Rt

30 ( ohm.m ) RLA3

1

Rt > Rxo

30 ( ohm.m ) RLA4

2D Invasion

1

Washout

TPL 27

7 ( ns/m ) EATT

100

0

3

MD 1 : 100 ft

20

1

( in ) Bit Radius 0

( in ) 700

( dB/m )

0

DCAL

( in )

1

20

1

20

1

30

1

30 ( ohm.m ) Rt from 1D Inversion

30

1

30

1

( ohm.m ) Rt from 2D Inversion ( ohm.m )

30 ( ohm.m ) Rxo from 2D Inversion

( ohm.m ) RLA5

( in ) Hole Radius 0

30 ( ohm.m ) Rxo from 2D Inversion

Invasion Rad Crossover

Rt from 2D Inversion

30 ( ohm.m ) RXO8

Standard 1D Rt computation

30 ( ohm.m )

XX00

XX10

XX20

XX30

Rt computed by 2D inversion

XX40

Raw measured data

XX50

XX60


XX70

34

Tools and Applications Lateralog Applications Hydrocarbon Saturation Resistivity Lateralog

•Lateralog •Determine Rt in medium to high saline muds. •ARI/HALS •Detect heterogeneous formations •Evaluate Horizontal wells •Compute formation dips •HRLA •Accurate determination of R t (modeling and inversion) •Clear indication of permeability


35




Schlumberger Chart Rcor-2b and Rcor-2c provides the hole size and mud resistivity corrections to the laterolog tool run centered and eccentered respectively

36



Schlumberger Tornado Chart helps in determining R t and Invasion Diameter from Lateralog measurements.


37



Lateralog Evaluation Techniques Limitations • Cannot be used in oil-based muds or air-filled holes • Poor when Rxo > Rt • Invasion limit of 60” • Affected by the tool string length/TLC/Groningen effect • Difficult to model HRLA • Tool string length/TLC/Groningen effect • Responses can be modeled


38


Hydrocarbon Saturation Resistivity Induction

The signal induced on the receiver due to the current flowing in the transmitter coil is many times greater in magnitude than the signal induced by the current flowing in the formation. Fortunately, the signals induced by the two currents are 90o out of phase and can be separated and measured. Ab u-Dh abi September, 2005

39

Tools and Applications Factors Affecting Inducti on Response Hydrocarbon Saturation Resistivity Induction

Direct Coupling

Direct coupling was previously defined as the signal directly induced in the receiver coil by the transmitter. The design of the receiver coils (mutually balanced) eliminates this signal while the tool is in air. When the tool is opposite a formation additional direct coupling signal exists as a result of the effects of the formation. Borehole Effects

The magnetic field produced by the transmitter must pass through the borehole on the way to the formation. The size of the borehole, type of material in the borehole, and the position of the tool in the borehole all affect the induction measurement. Ab u-Dh abi September, 2005

40




Early tools used the mechanical placement of transmitter and receiver coils to achieve the desired depth of investigation and vertical resolution. These tools are called fixed focus. Array induction tools have a transmitter and an array of receiver coils and achieve the desired focusing via processing.

41




The phasor induction log consists of IDPH and IMPH curve. In water-based mud, a spherically focused laterolog (SFL) and an SP curve can also be recorded. 42



Along with the 10", 20", 30", 60", 90" depths of investigation resistivity curves, an image of the radial invasion can also be produced


43



Induction Applications • Determines Rt in oil and fresh-water-based mud • AIT - Accurate determination of Rt through modeling and inversion (thin and invaded beds) • AIT - Quantification of invaded fluid volumes


44

Tools and Applications Induction Environmental Corrections Hydrocarbon Saturation

Borehole Effects Induct ion Tools measure condu ctiv ity and s ee borehole enviro nment as:

Resistivity Induction

Cm – Better in oil base mud, high resistivity mud. Fresh mud is good. Worst in salty mud. Cmc – Usually neglected as very small. Cxo – Depends on Rmf , needs to be know. Ct – To be determined.


45



Induction Borehole Corrections • The tools DIL/DIT have to be corrected for Borehole Effects • Compute BH Geometrical Factor • Find additional sign due to borehole • Convert log resistivity into conductivity • Remove borehole signal from total signal • Convert result back to resistivity • Possible to apply using chart-books, but better left to computers


46



DIL/DIT

The computation of the R t and di from the induction log assumes a step invasion profile. Tornado charts are available to solve the Rt and di, from the borehole and shoulder bed corrected logs.


47

Tools and Applications An nulu s Inv asi on


100%

Borehole Wall 0%

The AIT makes no assumptions about the resistivity distribution when determining the five resistivity measurements. Thus, the AIT log is able to detect the annulus invasion. When a proper model is used, the log can also determine the R t in such cases.

Invaded Transition

Invaded Transtion


Annulus

Annulus

Virgin

Virgin

48



Induction Evaluation Techniques Limitations Induction • Cannot be used in salt-saturated muds • Poor when Rxo < Rt • Cannot be used in High resistivity formations • Poor in thin beds • Dipping beds will affect the log response AIT • Extends the working environment • Responses can be modeled


49

Tools and Applications Induction x Lateralog Logging Tool


Invaded Zone

Borehole

Uninvaded R x o R m

R t

o l o g L a t e r

R m

R x o


R t

n s e e s p o R n t i o I n d u c

50



Lateralog

Induction

Oil Base Mud

No

Yes

Salt Base Mud

Yes

Possible

Fresh Mud


2

Possible

Yes

Air Filled BH

No

Yes

High RT

Yes

No

Low RT

Possible

RT > RXO

Preferred

RT < RXO

3

1

Yes

Preferred

1.Possible if the follow ing Hole is small and in gauge Rt /Rm is low Tool position in BH is well known 2. Possible if R t /Rm is high 3.Possible if tool stringlength correction applied


The table provides the guidelines for the particular log to use under different conditions for the determination of R t.

51

Tools and Applications Comparison AIT to HRLA Hydrocarbon Saturation Resistivity Induction

Diameter = 8” Rt = 200 ohm.m Rxo = 30 ohm .m Rm = 0.1 ohm.m S/O = 1.5”


52

Tools and Applications Comparison AIT to HRLA Hydrocarbon Saturation Resistivity Induction

Diameter = 8” Rt = 5 ohm.m Rxo = 30 ohm .m Rm = 0.1ohm.m S/O = 1.5”


53

Tools and Applications Modeling and Inversion Properties Calculated


Measured

Forward Modeling of Tool Response


INVERSION = UPDATE MODEL

No

Comparable ??

Yes

True Reservoir Model The iterative forward modeling is done till a good fit between the calculated log and the actually measured log is achieved (inversion). The process is outlined in the flowchart. Ab u-Dh abi September, 2005

54

Tools and Applications Modeling of the Resistivity Tool Response Hydrocarbon Saturation

1D Model

1D Model (analytical): Includes: d eviatian and layering Neglects: Borehole, mud, invasion Useful for induc tion tools

2D Model

2D Model (hybri d): Includes: layering, borehole, mud, invasion Neglects: borehole deviation Minimum fo r lateralog

Resistivity Induction Mathematically simulating the full reservoir geometry and tool physics is very complicated and time consuming. Therefore, approximations have to be made, so that a limited number of parameters are required to be solved.

3D Model (numeric al): Includes: everything

3D Model


55

Handout_8

Recommend Documents