CONCEPTS OF PETROLEUM GEOLOGY AN INTRODUCTION WORKSHOP ON “ TECHNOLOGY IMPERATIVES FOR EXPLORATION AND PRODUCTION OF OIL & GAS”
OIL AND NATURAL GAS CORPORATION LTD. LTD. 21st 21st TO 24th 24th DECEM DECEMBER BER - 2009 2009 SIBSAGAR
PETROLEUM GEOLOGY REFERS TO THE SPECIFIC SET OF GEOLOGICAL DISCIPLINES THAT ARE APPLIED TO THE SEARCH FOR HYDROCARBONS DURING OIL EXPLORATION PETROLEUM GEOLOGY IS PRINCIPALLY CONCERNED WITH THE EVALUATION OF SEVEN KEY ELEMENTS IN A SEDIMENTARY BASIN TO OBTAIN AN IDEA OF THE SUBSURFACE AND OVERALL PETROLEUM SYSTEM.
Source Reservoir Seal Trap Timing Maturatio tion n and Migrat Migration ion Matura
1. EVALUATION OF THE SOURCE This involves quantification and evaluation of the nature of organic-rich rocks so that the type and quality of expelled hydrocarbon in a basin can be assessed by GEOCHEMICAL methods of analysis. STEPS IN SOURCE ROCK ANALYSIS
First establish likelihood of presence of organic-rich sediments deposited in the past on the basis of studies of local stratigraphy, paleogeography and sedimentology of the area. Identification and delineation of area of potential source rock. Determine the type of KEROGEN and state of its maturation. Calculation of thermal maturity and timing of maturation. Finally determine determine the the likelihood likelihood of oil / gas gas generation generation in the the area Finally and calculate the depth of oil window. (Majori (Maj ority ty of oil oi l generat generation ion occur occurs s in the the 60° 60° to 120° 120°C range. range. Gas generation starts at similar temperatures, but may continue continue up beyond beyond this this range, perhaps perhaps as high hi gh as 200°C.) 200°C.)
GEOCHEMICAL LOG H Index
Organic Carbon
Hydrogen yield % wt
Vro
H/C indications
2.THE RESERVOIR It is a porous and permeable lithological unit or set of units that holds the hydrocarbon reserves. The common types include sandstone and limestone. STEPS IN ANALYSIS OF RESERVOIRS First determine the type of lithofacies of the reservoir.
Assessment of their POROSITY (to calculate the t he volume of in situ hydrocarbons) situ hydrocarbons) and PERMEABILITY (to calculate how easily hydrocarbons will flow out of them). Study the Post depositional Diagenetic changes in reservoir. Establish depositional environment and geometry of the reservoirs. Some of the key disciplines used in reservoir analysis are stratigraphy, stratigraphy, sedimentology, reservoir engineering and the technique of Formation evaluation using wireline tools. tools. rocks generated Siesmic attributes of subsurface through seismic data processing are used to infer
RESERVOIR ROCK
8
5
CC#21
1
8
7
CC#20
6
4
RESERVOIR ROCKS
3. TH THE SEA EAL L OR OR CAP ROCK CAP ROCK It is a unit with low permeability that impedes the escape of hydrocarbons from the reservoir rock. Common SHALE.
seals
include
EVAPORITES,
CHALKS
and
Analysis of seals involves assessment of their thickness and extent, such that their effectiveness can be quantified. 4. THE TRAP It is the stratigraphic or structural feature that ensures the juxtaposition of reservoir and seal such that hydrocarbons remain trapped in the subsurface, rather than escaping and being lost. The common types are Structural, Stratigraphic and Combination Traps.
SURFACE
OIL SEEP
Oil accumulation in trap
SOURCE KITCHEN AREA
A structural trap, where a fault has juxtaposed a porous and permeable reservoir against an impermeable seal. Oil (shown in red) accumulates against the seal, to the depth of the base of the seal. Any further oil migrating in from the source will escape to the surface and seep.
TYPES OF TRAPS STRUCTURAL TRAP: Here the trap has been produced by deformation of the beds after they were deposited, either by folding or faulting. STRATIGRAPHIC TRAP: TRAP: Here the trap is formed by changes in the nature of the rocks themselves, or in their layering, the only structural effect being a tilt to allow the oil to migrate through the reservoir. COMBINATION TRAPS: Here the trap is formed partly by structural structural and partly partly by stratig stratigraphic raphic effects, effects, but but not entirely entirely due to either. HYDRODYNAMIC TRAPS: TRAPS: These Traps is due to water flowing through the reservoir and holding the oil in places where it would not otherwise be trapped.
COMMON TRAP TYPES Structural
Structural
Structural
COMMON TRAP TYPES
5. AN ANAL ALYS YSIS IS OF MA MATU TURA RATI TION ON It involves assessing the thermal history of the source rock in order to make predictions of the amount and timing of hydrocarbon generation and expulsion.
6&7. THE TIME AND NATURE OF MIGRATION Finally, the careful studies of reveal information on how hydrocarbons move from source to reservoir and help quantify the source (or kitchen ) of hydrocarbons in a particular area.
Extreme Global Warming gave excessive Algal Growths
90 & 150 million years ago
Organ rganic ic deb ebri ris s
Rifts formed as the Continents moved apart
And t hen he n cam cam e t he rains
Chemical reactions converted organic debris into oil when buried & heated
Rifts filled by sediment washed in from borderlands
Generation Migration Entrapment
Gas Cap Oil
Accumulation Entrapment Acc ccumulation umulation
Water
Seal Rock Reservoir Rock Rock
Migration 120°Critical F
Source Rock
Generation
Temperature 0C 60-120 350° F 24803
JMA JMA
ORIGIN OF PETROLEUM FORMS Petroleum
is derived from the remains of living things which contains a material called kerogen. Before dead organic matter becomes petroleum with time, the kerogen kerogen matures matures into into an assortm assortment ent of hydroc hydrocarbon arbon molecules of all sizes and weights. The lightest (small) hydrocarbon molecules waft away as natural gas, and the heavier ones make up an oily liquid. Petroleum source rocks are of terrestrial and marine origin. Terrestrial source rocks are deposited in lakes, delta and river basins having woody plant matter, algae etc. Marine source rocks contain dead planktons, algae, organic remains etc. In both the settings, the mixture is buried under conditions of no oxygen. oxygen. The The kerogen kerogen are classi classified fied as type type I,II I,II & III as per their origin and are capable of producing oil or gas or both.
Under the anaerobic anaerobic conditions, conditions, the kerogen kerogen is transfo transformed rmed into a flammable substance called bitumen by the action of heat and
anaerobic microbes in the sediment and natural
catalysts.
Most of the bitumen is eventually cooked into tarry asphalt releasing hydrocarbon molecules (as well as water and carbon dioxide) out of the source rock as it heats.
Heavy oils form first, then light oils. As temperatures rise to and above above 100° C, source source rocks rocks produce produce more gas. gas .
Being lighter than rocks, petroleum tends to rise upward through fractures and the pores of coarse sandstone beds.
A small fraction of that leakage, perhaps 2% is preserved in large pools having an impermeable cap / seal over it.
CHARACTERISTICS OF PETROLEUM RESERVOIRS A reservoir is sponge-like rock with open space between its grains -porosity. The porosity may be primary or it might be secondary as groundwater dissolves pores in the rock or as minerals undergo alteration or may have formed due to tectonic activities. One source of porosity is the transformation of calcite to dolomite by fluids rich in magnesium, which takes up less space. Besides porosity, there must be high permeability ie. the connectedness of pores that allows fluid to move easily through the reservoir rock. Permeability, porosity in combination with geologic structure are all of interest to petroleum petroleum geologists as it provides sites of hydrocarbon accumulation under favourable conditions.
BASIC POROSITY TYPES
POROSITY TYPES IN LIMESTONE
Mold Moldic ic poro porosi sity ty
Matrix porosity
EXPLORATION CYCLE IN A SEDIMENTARY BASIN
Geological Field Mapping / Remote sensing Gravity Magnetic Surveys
Seismic Data API (2D/3D) Prospect Identification
Drilling
BHS & Simulation
Reservoir Studies Production
Well Logs & VSP
EXPLORATION ACTIVITIES IN A SEDIMENTARY BASIN
GEOLOGICAL MAPPING : REGIONAL MAPS GEOCHEMICAL PROSPECTING: ANOMALY MAPS GEOPHYSICAL PROSPECTING GRAVIT GRAVITY Y – MAGNET MAGNETIC IC SURVE SURVEY: Y: MAPS MAPS SEISMI SEISMIC C SURVEY SURVEY – 2D & 3D 3D : ISOCH ISOCHRON RON MAPS MAPS PROSPECT IDENTIFICATION ESTABLISHING STRATIGRAPHY : Age determination DEPOSITIONAL ENVIRONMENTS: Facies modeling SOURCE ROCK GEOCHEMISTRY: Maturation SYNTHESIS AND ATTRIBUTE MAPPING STRUCTURE AND TECTONIC MAKEUP PREPARATION OF ISOCHRON-STRUCTURE MAPS DRILLING AND SYNTHESIS OF SUBSURFACE DATA RESERVOIR MODELLING & DEVELOPMENT SCHEME
GEOLOGICAL MAP AND CROSS SECTION OF AREA
Geological map
Geological section
GEOCHEMICAL MAPS Etah Et ah ar area ea,, Gang Ganga a Basin Basin
Isochr Isochron on map at the base base of of Tertiary
Geochemical anomaly
BEAS FAULT
RESIDUAL GRAVITY MAP OF NORTHERN PART OF PUNJAB PLAINS
MAGNETIC ANOMALY MAP (VERTICAL COMPONENT) Pathankot
N DINANAGAR HIGH
Batala
M U L K O E R I W A N t t l u a - D f H T a s A S e I G R BH I U H Y E G H A - T N R H E O S T D R N D
E N D
H
Jalandhar
0
10000
20000
30000
L O I G A D H A W M T P R U E T R L O B R N D W A S E N E T M R E D E N T N D R I D G E
H I A R P U R L O W
40000
Scale (meters)
after after Goha Goha et al
Punjab Plains
Seismic Acquisition
Seismic Data Acquisition Geometries Shot 1
*
*
Seismic Energy Source
Geophones
PROCESSED SEISMIC SECTION
INTERPRETED SEISMIC SECTION
Eocene K/T Kumbakonam ridge
Turonian Albian Tranquebar Sub-basin
Karaikal ridge
PROBABLE TRAPPING MECHANISM FOR HYDROCARBONS HYDROCARBON S IDENTIFIED BY SEISMIC SURVEY
PROSPECT IDENTIFICATION GS-15-9
GS-46-1
GAS SAND
T C U O O I L O P M I O
PRESENT DEPTH
TARGET DEPTH
RANDOM SEISMIC LINE THROUGH PROSPECT GS-15-9
DEPOSITIONAL ENVIRONMENT
AND ITS CHARACTERISTIC LITHOFACIES
SPITI-ZANSKAR
KAREWA
SEDIMENTARY BASIN MAP OF INDIA
HIMALAYAN FORELAND
AREA 3.14 Million Sq. Km Km..
RAJASTHAN
ASSAM SHELF
DAMODAR
GANGA
ASSAM-ARAKAN FOLD BELT
CAMBAY
SAURASHTRA
KUTCH
VINDHYAN
SOUTH REWA
BENGAL
SATPURA NARMADA BOMBAY OFF.
KORICOMORIN DEEP OFF.
DECCAN SYNECLISE
BHIMAKALADGI
CUDDAPAH KERALA - KONKAN -
CHATTISGARH BASTAR
BAY OF BENGAL MAHANADI
KRISHNA GODAVARI
PRANHITAGODAVARI
LEGEND CATEGO CATEGORY RY - I BAS BASIN IN CATEGORY CATEGORY - II BASIN BASIN CATEGORY CATEGORY - III BASIN CATEGORY CATEGORY - IV BASIN DEEP SEA BASIN PRE-CAMBRIAN BASEMENT / TECTONISED SEDIMENTS
0
85 E DEEP OFFSHORE
ANDAMAN NICOBAR
NARCODAM DEEP OFFSHORE
CAUVERY
After – Jokhan ram et-al.
GLACIAL-ALLUVIAL FANS-FLUVIAL-LACUSTRINE-DELTA AND MARINE DEPOSITIONAL ENVIRONMENTS
ALLUVIAL FAN DEPOSITS
TIDAL DEPOSITIONAL ENVIRONMENT
DEEP WATER DEPOSITIONAL ENVIRONMENT
CHARACTERISTICS OF DEEP WATER SEDIMENTS. Basin: Cauvery
FORMATION : KAMALAPURAM
Age : Eocene
Bathymetry: Bathyal Interpretation: SLUMP FACIES PG
f
CO
CO con S
R
s
C
l
A
B
C
f
D
Core photograph of segments segments in enlarged view from (CC-2 &3) KMP-19. “A” (1966-1966.25m), “B” (1974.85 -1975.0m) represents, convolute bedding (CO). Photos C & D are from CC-2&3 CC-2&3 of KMP-35. “C” (1868.60-1868.90m) show slump (S) and convolute layer and at bottom with parallel oriented clasts (C ) in laminar flow (l) with primary glide plane (PG). “D” (1872.75-1873.10m) shows two freezing flow (f) with contact (Con). Liquefied Lique fied slump (s) towards the top of bottom flow.
INTEGRATION AND UNDERSTANDING OF THE CONCEPTS OF PETROLEUM GEOLOGY IN INDIAN SEDMENTARY BASIN LED TO DISCOVERY OF SIGNIFICANT HYDROCARBON DISCOVERIES. 1967: Rajasth an Basin 1958: Camba y Basin 1974: Mumbai Offshor e
1889: Assa m Shelf * 1973: A&AA FB 1980: KG Basin 1985: Cauve ry Basin
UNDERSTANDING OF THE CONCEPT OF
PETROLEUM GEOLOGY
IS A CONTINUOUS PROCESS AND
WE NEED YOUR PARTICIPATION
TO HAVE MORE SUCH DISCOVERIES
