petroleum geology oct2 stim
TRANSCRIPT
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Petroleum Geology
© Copyright 2003 Schlumberger. Unpublished work. All rights reserved. This work contains confidential and proprietary trade secrets of Schlumberger and may not be copied or stored in an informational retrieval system, transferred, used, distributed, translated or retransmitted in any form or by any means, electronic or
mechanical, in whole or part, without the express written permission of the copyright owner.
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Outline Petroleum systems Geologic principles and geologic time Rock and minerals, rock cycle, reservoir
properties Hydrocarbon origin, migration and
accumulation Sedimentary environments; stratigraphic traps Plate tectonics, structural geology Structural traps Geophysical methods Importance to Schlumberger
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Petroleum System A Petroleum System requires timely convergence of certain geologic factors and geologic events.
These Include:
Mature source rockMigrationReservoir rockSeal or cap rock
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Cross Section Of A Petroleum System
Overburden Rock
Seal or Cap[Rock
Reservoir Rock
Source Rock
Underburden Rock
Basement Rock
Top Oil Window
Top Gas Window
Geographic Extent of Petroleum System
Petroleum Reservoir (R)
Fold-and-Thrust Belt(arrows indicate relative fault motion)
EssentialElements
ofPetroleum
System
(Foreland Basin Example)
(modified from Magoon and Dow, 1994)
Reservoir
Sed
imen
tary
Bas
in F
ill
R
Stratigraphic Extent of
PetroleumSystem
Active Source Rock
Extent of Play
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Basic Geologic Principles
Uniformitarianism - “The present is the key to the past.”
Original Horizonality - “Sedimentary layers are deposited in a horizontal or nearly horizontal position.”
Superposition - “Younger sedimentary beds occur on top of older beds, unless they have been overturned or faulted.”
Cross-Cutting Relations - “Any geologic feature that cuts another geologic feature is younger than the feature that it cuts.”
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Cross-Cutting Relationships
Angular Unconformity
Igneous Sill
A
B
C
D
EF
GHIJ
K
IgneousDike
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Fall 2003 EASA-123 Intro to Earthquakes Lecture-3 17
Mechanical Layers:
1. Lithosphere
2. Asthenosphere
3. Mesosphere
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0
50
100
150
200
250
300
350
400
450
500
550
600
0
10
20
30
40
50
60
Cry
pto
zoic
(Pre
cam
bri
an)
Phanerozoic
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Pennsylvanian
Mississippian
Devonian
Silurian
Ordovician
Cambrian
Mill
ion
s o
f y
ears
ag
o
Mill
ion
s o
f y
ears
ag
o
Bill
ion
s o
f y
ears
ag
o0
1
2
3
4
4.6
Paleocene
Eocene
Oligocene
Miocene
Pliocene
PleistoceneRecent
Qu
ater
nar
yp
erio
d
Ter
tiar
y p
erio
d
Eon Era Period Epoch
Geologic Time Chart
Pal
eozo
icM
esoz
oic
Ce
noz
oic
Era
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Triassic periodJurassic period Permian period
Pennsylvanian periodMississippian period
2 b.y Evolution of cells with nucleus
3 b.y Firstfossilcells
4 b.y Oldest rocksdated on Earth
4.6 billionyears ago
1 b.y
146 m.y
245 m.y323 m.y
363 m.y
65 m.y
57 m.y
35 m.y
23 m.y
5 m.y
ERAPERIOD
Holocene epoch
570 m.y510 m.y
439 m.y
409 m.y
Geologic Time Scale - Biostratigraphy
Devonian period
Silurian period
EPOCH
0.01 m.y
290 m.y208 m.y
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Rocks
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Classification of RocksSEDIMENTARY
Ro
ck-f
orm
ing
pro
cess
So
urc
e o
fm
ater
ial
IGNEOUS
METAMORPHIC
Molten materials in deep crust andupper mantle
Crystallization(Solidification of melt)
Weathering anderosion of rocks
exposed at surface
Sedimentation, burial and lithification
Rocks under high temperatures
and pressures in deep crust
Recrystallization due toheat, pressure, or
chemically active fluids
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The Rock Cycle
Magma
MetamorphicRock
SedimentaryRock
IgneousRock
Sediment
Heat and Pressure
Weathering,Transportationand Deposition
Weathering, Transportation,
and Deposition
Cooling and
SolidificationM
eltin
g (Crystalization)
Hea
t And
Pre
ssur
e
(Met
amor
phis
m)
Weathering,
Transportation
And D
eposition
Cementation andCompaction(Lithification)
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Igneous RocksComprise 95% of the Earth's crust.
Originated from the solidification of molten material from deep inside the Earth.
There are two types:
•Volcanic - glassy in texture due to fast cooling.
•Plutonic - slow-cooling, crystalline rocks.
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Igneous Rocks and Reservoirs
Igneous rocks can be part of reservoirs. Fractured granites form reservoirs in some parts of the
world. Volcanic tuffs are mixed with sand in some reservoirs.
Example: Granite Wash - Elk City, Okla., Northern Alberta,CA
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Metamorphic Rocks 2) Metamorphic rocks formed by the action of temperature and/or pressure on
sedimentary or igneous rocks.
Examples are• Marble - formed from limestone• Hornfels - from shale or tuff• Gneiss - similar to granite but formed by metamorphosis
Field Example:
1. Point Arguello - Monterey Formation is actually layers of fractured Chert and Shale. Oil is in the fractures
2. Long Beach, Calif. - Many SS producers on an Anticline above fractured Metamorphic basement rock
3. Austin, TX eastward - Lava flows of Basalt (Serpentine) from Volcanoes in ancient Gulf of Mexico
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Sedimentary Rocks These are the most important for the oil industry as it
contains most of the source rocks and cap rocks and a majority of the reservoirs.
Sedimentary rocks come from the debris of older rocks and are split into two categories
Clastic and Non-clastic.• Clastic rocks - formed from the materials of older rocks by
the actions of erosion, transportation and deposition.
• Non-clastic rocks - from chemical or biological origin and then deposition.
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Rock ClassificationClasticsRock type Particle diameter Conglomerate Pebbles 2 - 64mm Sandstone Sand .06 - 2mm Siltstone Silt .004 - .06mm or 4 to 65 microns Shale Clay < .004mm or 4 microns
Non-ClasticsRock type Composition Limestone CaCO3 Dolomite CaMg(CO3)2 Salt NaCl Anhydrite CaSO4 Gypsum CaSO4.2H2O Coal Carbon
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Siltstone, mudand shale
~75%
Sedimentary Rock Types
• Relative abundanceSandstone
and conglomerate~11%
Limestone anddolomite
~13%
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Depositional Environments The depositional environment can be Shallow or deep water. Marine (sea) and lake or continental. This environment determines many of the
reservoir characteristics
Frigg Gas Field - North Sea
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Depositional Environments Continental deposits are usually dunes. A shallow marine environment has a lot of turbulence hence varied
grain sizes. It can also have carbonate and evaporite formation. A deep marine environment produces fine sediments.
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Depositional Environments
The depositional characteristics of the rocks lead to some of their properties and the reservoir property.• The reservoir rock type clastic or non-clastic.• The type of porosity (especially in carbonates) is
determined by the environment plus subsequent events.
The structure of a reservoir can also be determined by deposition; a river, a delta, a reef etc.
This can also lead to permeability and producibility of these properties are often changed by further events.
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Clastic Reservoirs
Consolidated and unconsolidate sands
Porosity• Determined mainly by the packing and mixing of
grains.
Permeability• Determined mainly by grain size and packing,
connectivity and shale content.
Fractures may be present.
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Clastic Sedimentary Rocks
BrecciaBreccia
SandstoneSandstone
ConglomerateConglomerate
ShaleShale
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Average Detrital Mineral Composition of Shale and Sandstone
Mineral Composition Shale (%) Sandstone (%)
Clay Minerals
Quartz
Feldspar
Rock Fragments
Carbonate
Organic Matter,Hematite, andOther Minerals
60
30
4
<5
3
<3
5
65
10-15
15
<1
<1
(modified from Blatt, 1982)
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Clastic Rocks
Clastic rocks are sands, silts and shales. The difference is in the size of the grains.
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Sedimentation
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Sedimentation
Sedimentary muds become sedimentary rocks.• Calcareous muds become limestone.• Sands become sandstone.
Grains in the matrix and the fluids reacting to create new minerals changing the matrix and porosity. Fluids can also change creating a new set of minerals.
This whole process is called Diagenesis.
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Environment Agent Of TransportationDeposition
Sediments
Alluvial Rivers Sand, gravel, mud
Lake Lake currents, waves Sand, mud
Desert Wind Sand, dust
Glacial Ice Sand, gravel, mud
Delta River + waves, tides Sand, mud
Beach Waves, tides Sand, gravel
Shallow shelf Waves, tides Sand, mud
Deep sea Ocean currents, settling Sand, Mud
Clastic Sedimentary Environments
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Depositional Environment - Delta
Sediments are transported to the basins by rivers. A common depositional environment is the delta where the river empties
into the sea. A good example of this is the Mississippi (Miocene and Oligocene
sands)
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Rivers
Some types of deposition occur in rivers and sand bars. The river forms a channel where sands are deposited in
layers. Rivers carry sediment down from the mountains which is then deposited in the river bed and on the flood plains at either side.
Changes in the environment can cause these sands to be overlain with a shale, trapping the reservoir rock.
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Fan Deposition
Example Alluvial sedimentation
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Sandstone Composition Framework Grains
Qtz
Qtz
Qtz
Qtz
Ankerite
Quartz
Quartz
Quartz
Qtz
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Scanning Electron MicrographNorphlet Formation, Offshore Alabama, USA
Pores Provide theVolume to ContainHydrocarbon Fluids
Pore Throats RestrictFluid Flow
PoreThroat
Porosity in Sandstone
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Secondary Electron Micrograph
Jurassic Norphlet SandstoneHatters Pond Field, Alabama, USA (Photograph by R.L. Kugler)
Illite
SignificantPermeabilityReduction
Negligible PorosityReduction
Migration ofFines Problem
High IrreducibleWater Saturation
Clay Minerals in Sandstone ReservoirsFibrous Authigenic Illite
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Secondary Electron Micrograph
Occurs as ThinCoats on DetritalGrain Surfaces
Occurs in SeveralDeeply BuriedSandstones WithHigh Reservoir Quality
Iron-Rich Varieties ReactWith Acid
Clay Minerals in Sandstone ReservoirsAuthigenic Chlorite
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Secondary Electron Micrograph
Carter SandstoneNorth Blowhorn Creek Oil UnitBlack Warrior Basin, Alabama, USA
Significant PermeabilityReduction
High Irreducible WaterSaturation
Migration of FinesProblem
(Photograph by R.L. Kugler)
Clay Minerals in Sandstone ReservoirsAuthigenic Kaolinite
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100
10
1
0.1
0.01 0.01
0.1
1
10
100
1000
2 6 10 14 2 6 10 14 18
Per
mea
bili
ty (
md
)
Porosity (%)
Authigenic Illite Authigenic Chlorite
(modified from Kugler and McHugh, 1990)
Effects of Clays on Reservoir Quality
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Carbonate Reservoirs Carbonates (limestone and dolomite) normally have a
very irregular structure.
Porosity:• Determined by the type of shells, etc. and by
depositional and post-depositional events (fracturing, leaching, etc.).
Permeability:• Determined by deposition and post-deposition events,
fractures.
Fractures can be very important in carbonate reservoirs.
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Carbonate types Chalk is a special form of limestone (CaCO3) and is
formed from the skeletons of small creatures (cocoliths).
Dolomite (CaMg(CO3)2) is formed by the replacement of some of the calcium by a lesser volume of magnesium in limestone by magnesium. Magnesium is smaller than calcium, hence the matrix becomes smaller and more porosity is created.
Evaporites such as Salt (NaCl) and Anhydrite (CaSO4) can also form in these environments.
40
Depositional Environment Carbonates
Carbonates are formed in shallow seas containing features such as:• Reefs.• Lagoons.• Shore-bars.
41
Diagenesis The environment can also involve subsequent alterations of the
rock such as:• Chemical changes.• Diagenesis is the chemical alteration of a rock after burial. An example
is the replacement of some of the calcium atoms in limestone by magnesium to form dolomite.
• Mechanical changes - fracturing in a tectonically-active region.
42
Hydrocarbon Generation, Migration, and Accumulation
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Source Rocks Hydrocarbon originates from minute organisms in seas
and lakes. When they die, they sink to the bottom where they form organic-rich "muds" in fine sediments.
These "muds" are in a reducing environment or "kitchen", which strips oxygen from the sediments leaving hydrogen and carbon.
The sediments are compacted to form organic-rich rocks with very low permeability.
The hydrocarbon can migrate very slowly to nearby porous rocks, displacing the original formation water.
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Hydrocarbon Migration
Hydrocarbon migration takes place in two stages:Primary migration - from the source rock to a porous rock. This is a complex process and not fully understood.It is probably limited to a few hundred metres.Secondary migration - along the porous rock to the trap.This occurs by buoyancy, capillary pressure and hydrodynamics through a continuous water-filled pore system.It can take place over large distances.
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Organic Matter in Sedimentary Rocks
Reflected-Light Micrographof Coal
Vitrinite
KerogenDisseminated Organic Matter inSedimentary Rocks That is Insolublein Oxidizing Acids, Bases, andOrganic Solvents.
VitriniteA nonfluorescent type of organic materialin petroleum source rocks derived primarily from woody material.
The reflectivity of vitrinite is one of thebest indicators of coal rank and thermalmaturity of petroleum source rock.
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Interpretation of Total Organic Carbon (TOC)(based on early oil window maturity)
HydrocarbonGenerationPotential
TOC in Shale(wt. %)
TOC in Carbonates(wt. %)
Poor
Fair
Good
Very Good
Excellent
0.0-0.5
0.5-1.0
1.0-2.0
2.0-5.0
>5.0
0.0-0.2
0.2-0.5
0.5-1.0
1.0-2.0
>2.0
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Plate Tectonics and Structural Geology
48
Elements of Plate Tectonics
Magma rising
Asthenosphere
Magma forming
• Earthquake centers
Oceaniccrust
Sea floor spreading
DIVERGENT BOUNDARYMid-ocean ridge
Volcanism
CONVERGENT BOUNDARYPlate subduction
Mountainbuilding
Continental crust
Deep-sea trench
Lithosphere
Lithosphere
49
Wrench fault
Sedimentary Basin andStress Fields
Pull-apart Basin(Lateral Stress)
Normal fault
Thrust fault
Foreland Basin(Compressive Stress)
Rift Related Basin(Extensional Stress)
Fault Types Basin Geometries
Sedimentary Fill
50
Structural Features
51
Folded Structures
Anticline Syncline
52
Fold Terminology
Anticline
Syncline
Oldest rock
Youngest rock
Modified from xxx)
Limb
Limb
N
Limb
53
H.W.
FaultScarp
Dow
nthrown
Upthrow
n
Strike direction
F.W.
Fault plane
Dip angle
Normal Fault
Key bed
Fault scarpD
ownthrow
n
Upthrow
n
F.W.
H.W.
Fault plane
Dipangle
Strike direction
Reverse Fault
Faults
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Faulting (normal faults)
Example Kabab Canyon, Utah
Photograph by XXX
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Strike Slip Fault(Left Lateral)
N
Fault Plane
Stri
ke Dip Angle
56
Heterogeneity
57
Geologic Reservoir Heterogeneity
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Scales of Geological Reservoir Heterogeneity
Fie
ld W
ide
Inte
rwel
lW
ell-B
ore
(modified from Weber, 1986)
Hand Lens orBinocular Microscope
Unaided Eye
Petrographic orScanning Electron
Microscope
DeterminedFrom Well Logs,Seismic Lines,
StatisticalModeling,
etc.
10-100'sm
10-100'smm
1-10'sm
100'sm
10'sm
1-10 km
100's m
Well WellInterwell
Area
ReservoirSandstone
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Hydrocarbon Traps
Structural traps
Stratigraphic traps
Combination traps
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Traps General
Ghawar Oilfield - Saudi Arabia- Ls - 145 mi x 13 mi wide x260 ftproduces 11,000 b/d total 82B bblsGasharan Oilfield - Iran - Ls - 6000ft. Net pay total 8.5 B bbls
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Structural Hydrocarbon Traps
SaltDiapir
Oil/WaterContact
GasOil/GasContact
Oil
ClosureOilShale Trap
Fracture Basement
(modified from Bjorlykke, 1989)
Fold Trap
Seal
OilSalt
Dome
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Fault Traps Faults occur when the rock shears due to stresses.
Reservoirs often form in these fault zones. A porous and permeable layer may trap fluids due to its
location alongside an impermeable fault or its juxtaposition alongside an impermeable bed.
Faults are found in conjunction with other structures such as anticlines, domes and salt domes.
Normal Faults - Nigeria,Hibenia (E. Canada), VicksburgTrends (Victoria, TX)
Drag Faults - Wyoming,most Rocky Mountains
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Stratigraphic Traps
Point Bars - Powder River Basin, WY, Clinton SS in Western Ok,
Michigan - Belle River Mills
Devonian reefs (Barriers and Atolls) - Alberta CA. (Leduc & Redwater)
Midland Basin &Delaware Basin of West TX - Barrier Reefs
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Petroleum Exploration: Geophysical Application to Petroleum Geology
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Petroleum Exploration-Geophysical Methods
Gravity methods
Magnetic surveys
Seismic surveys
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-3-2-1+1
Salt2.1 gm/cm3
Corrected Gravity(Bouguer Anomaly)
UncorrectedGravity
Clastics2.4 gm/cm3
Meter
GravityValue (mgal)
Principle of Gravity Surveys
67
Principle of Magnetic Surveys
+
-
Basement
Sedimentary Basin
Magnetization
Measured
(from xxx, 19xx)
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Seismic Surveys
The seismic tools commonly used in the oil and gas industry are 2-D and 3-D seismic data
Seismic data are used to:– Define and map structural folds and faults– Identify stratigraphic variations and map
sedimentary facies– Infer the presence of hydrocarbons
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Pre-Drilling Knowledge Exploration
Structural information obtained from surface seismic data. Rough geological information can be provided by nearby wells
or outcrops. Approximate depths estimated from surface seismic data.
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Sea bed
Boat
Cable with hydrophones
Sea Surface
Source(Airguns)
Sedimentary Layers
Incidentwaves Reflected
waves
Marine Acquisition System
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Crossline 470 (East)
N S
Source
Reservoirs
Seal (unconformity)
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Applications of Seismic Data
Make a structural model of the reservoir
Delineate and map reservoir-quality rocks
Establish gas/water contacts
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00
-11
60
0
W
N
m
0 3000
0 1000
ft
-11,600-12,000
-12,000-12,400
11,400-11,600
Top Misoa C-4 SandElevation (ft)Sea-level datum
-12,400-12,800
-12,800-13,200
OW
OW
O
Structural Map, VLE 196 Field
N
Structural interpretationbased on 3-D seismic and well log data
74
SeismicAmplitude
Mapof a
Horizon
Channels
Modified from Brown, 1996
3-D Seismic datadefine reservoir-quality,channel-fillsand deposits
75
Fluid Level Boundaries on 3-D Data
Modified from Brown, 1996
Not Interpreted Interpreted
Flat spot on seismic line indicates petroleum / water contact
Fault
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4-D Seismic Surveys
The “4” in 4-D seismic is time A 4-D survey means that at least two 3-D
seismic surveys have been made at different times over the same field
Reflection character (attributes) change through time
These changes result from migration of the water contact in the reservoir
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Importance to Schlumberger
Source of revenue. Allows our Engineers to:
• Better understand the limitations of a reservoir.• Design better treatments
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STS51C-143-0027 Mississippi River Delta and Coastal Louisiana, U.S.A. January 1985
NASA PHOTO
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STS61A-42-0051 Mississippi River Delta, Louisiana, U.S.A.October 1985
NASA PHOTO
20 mi
N
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Exercises:Petroleum Geology
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Exercise 11. Oil forms at lower temperatures than gas. T_____ F ______
2. The law of (original horizontality, uniformitarianism, superposition) states that, in a normal sedimentary sequence, younger layers occur on top of older layers.
3. The largest division of geologic time is the (era, eon, period, epoch).
4. Hydrocarbons are most abundant in (metamorphic, igneous, sedimentary) rocks.
5. The most abundant sedimentary rock type is shale. T____ F ______
6. Name 3 clay minerals common in sandstone reservoirs
A. _____________________ B.____________________ C. ____________________
7. Clastic rocks are formed from the materials of older rocks by the actions of erosion, transportation and __________________.
8. Clastic rocks are sedimentary. T___ F____
9. Name two non-clastic sedimentary rocks. A.______________ B.________________
10. Alluvial, desert, delta, beach and shallow shelf sediment make the best reservoirs
T_______ F_______
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Exercise 21. 1. Diagenesis is the chemical alteration of a rock after burial. T___ F ___
2. (Magnesium, Iron, or Sulfate) must be in the formation water in order to convert limestone to dolomite.
3. Limestone is (CaCO3 or Ca(CO3)2).
4. Dolomite is MgCaCO3 or MgCa(CO3)2.
5. Reef deposits are classified as (clastic, carbonate) sedimentary rocks.
6. The source rock must contain (organic material, coal, methane).
7. Fault and anticline traps occur only in gas wells. T___ F___
8. The oil water contact can be observed using seismic T___ F___
9. (Historical, structural, tectonic) geology addresses the occurrence and origin of smaller scale deformational features, such as folds and faults, that may be involved in hydrocarbon migration or which may form structural hydrocarbon traps.
10. Good quality sandstone reservoirs normally contain ~ (1-10 or 25-30% silt and clay).
83
N
a b
c d
23
1
4
34 4
Well
Exercise 3
Well
84
Exercise 41. Hydrocarbons reservoirs are normally in (igneous,
metamorphic, sedimentary) rocks.
2. Fluorescence of drill cuttings or core indicates (oil, gas, water) is present.
3. Reservoir traps are (very impermeable, highly permeable).
3. What are 2 uses of seismic data in petroleum exploration and development?
1. ________________________________________________
2. _________________________________________________
4. In inclined reservoir rocks, what is the significance of a “flat spot” in seismic sections?
5. What is a 4-D seismic evaluation?