CONCEPTS OF
PETROLEUM GEOLOGY
AN INTRODUCTION
WORKSHOP ON
“ TECHNOLOGY IMPERATIVES
FOR EXPLORATION AND PRODUCTION
OF OIL & GAS”
OIL AND NATURAL GAS CORPORATION LTD.
21st TO 24th DECEMBER - 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
™ Maturation and Migration
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
¾ 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.
¾ Identification and delineation of area of potential source rock.
¾ Determine the type of KEROGEN and state of its maturation.
¾ Calculation of thermal maturity and timing of maturation.
¾ Finally determine the likelihood of oil / gas generation in the area
and calculate the depth of oil window.
(Majority of oil generation occurs in the 60° to 120°C range.
Gas generation starts at similar temperatures, but may
continue up beyond this range, perhaps as high as 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 volume of
in 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.
¾ Some of the key disciplines used in reservoir analysis are
stratigraphy, sedimentology, reservoir engineering and the
technique of Formation evaluation using wireline tools.
¾Siesmic attributes of subsurface
rocks generated
through seismic data processing are used to infer
physical / sedimentary properties of the rocks.
RESERVOIR ROCK
8
5
CC#21
1
8
7
CC#20
6
4
RESERVOIR ROCKS
3. THE SEAL OR 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: 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 and partly by stratigraphic effects, but not entirely
due to either.
HYDRODYNAMIC 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. ANALYSIS OF MATURATION
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
Organic debris
Rifts formed as
the Continents
moved apart
And then came the 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
Water
Seal Rock
Reservoir
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 matures into an assortment of hydrocarbon
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. The kerogen are classified as type I,II & III
as per their origin and are capable of producing oil or gas
or both.
™ Under the anaerobic conditions, the kerogen is transformed
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 100° C, source rocks produce more 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
9 A reservoir is sponge-like rock with open space between
its grains -porosity.
9 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.
9 One source of porosity is the transformation of calcite to
dolomite by fluids rich in magnesium, which takes up less
space.
9 Besides porosity, there must be high permeability ie. the
connectedness of pores that allows fluid to move easily
through the reservoir rock.
9 Permeability, porosity in combination with geologic
structure are all of interest to petroleum geologists as it
provides sites of hydrocarbon accumulation under
favourable conditions.
BASIC POROSITY TYPES
POROSITY TYPES IN LIMESTONE
Moldic porosity
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
GRAVITY – MAGNETIC SURVEY: MAPS
SEISMIC SURVEY – 2D & 3D : ISOCHRON 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 area, Ganga Basin
Isochron map at the base of
Tertiary
Geochemical anomaly
map
BEAS FAULT
RESIDUAL GRAVITY MAP OF NORTHERN PART OF PUNJAB PLAINS
MAGNETIC ANOMALY MAP (VERTICAL COMPONENT)
Pathankot
N
DINANAGAR HIGH
M
W
LO
Batala
GH
HI
O
SH
I
AR
PU
R
LO
D
D
DG
EN N
RI
T
TR
R E EN
GH T
EM N D
HI W
AS
E
LO R B TR
PU O W
W
AM
AD
Jalandhar
AS
UY
AH
D
EN
TR
ND
D
E
TR
EN
GH
TR
HI
B
lt
fau
s
ea
UK
ER
IA
ND
L
E
0
10000
20000
30000
40000
Scale (meters)
after 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 IDENTIFIED BY SEISMIC SURVEY
PROSPECT IDENTIFICATION
GS-15-9
GAS SAND
CUT
O
I
PL
MI O
PRESENT DEPTH
TARGET DEPTH
RANDOM SEISMIC LINE THROUGH PROSPECT GS-15-9
GS-46-1
DEPOSITIONAL ENVIRONMENT
AND ITS CHARACTERISTIC LITHOFACIES
SPITI-ZANSKAR
KAREWA
SEDIMENTARY BASIN MAP
OF INDIA
HIMALAYAN FORELAND
AREA 3.14 Million Sq. 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
MAHANADI
PRANHITAGODAVARI
BHIMAKALADGI
CUDDAPAH
KERALA - KONKAN -
CHATTISGARH
BASTAR
BAY
OF
BENGAL
KRISHNA
GODAVARI
LEGEND
CATEGORY - I BASIN
CATEGORY - II BASIN
CATEGORY - III BASIN
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 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 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 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