petroleum geology
TRANSCRIPT
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Petroleum Geology
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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 WindowTop 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
Sedi
men
tary
Bas
in F
ill
R
Stratigraphic Extent of
PetroleumSystem
ActiveSource 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
GHIJK
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
ptoz
oic
(Pre
cam
bria
n)
Phanerozoic
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
PermianPennsylvanian
Mississippian
Devonian
Silurian
Ordovician
Cambrian
Mill
ions
of y
ears
ago
Mill
ions
of y
ears
ago
Bill
ions
of y
ears
ago
0
1
2
3
4
4.6
Paleocene
Eocene
Oligocene
Miocene
PliocenePleistoceneRecent
Qua
tern
ary
perio
dTe
rtia
rype
riod
Eon Era Period Epoch
Geologic Time Chart
Pal
eozo
icM
esoz
oic
Cen
ozoi
c Er
a
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Rocks
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Classification of RocksSEDIMENTARY
Roc
k-fo
rmin
gpr
oces
sSo
urce
of
mat
eria
l
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
SolidificationMelt
ing (Crystalization)
Hea
tAnd
Pres
sure
(Met
amor
phis
m)
Weathering,
TransportationAnd
Deposition
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 abundance
Sandstoneand 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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100
10
1
0.1
0.01 0.01
0.1
1
10
100
1000
2 6 10 14 2 6 10 14 18
Perm
eabi
lity
(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.
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Depositional Environment Carbonates
Carbonates are formed in shallow seas containing features such as:• Reefs.• Lagoons.• Shore-bars.
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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.
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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
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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
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Structural Features
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Folded Structures
Anticline Syncline
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Fold Terminology
Anticline
SynclineOldest rock
Youngest rock
Modified from xxx)
Limb
Limb
N
Limb
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H.W.
FaultScarp
Downthrown
Upthrown
Strike direction
F.W.
Fault planeDip 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
Strik
e Dip Angle
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Heterogeneity
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Geologic Reservoir Heterogeneity
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Scales of Geological Reservoir Heterogeneity
Fiel
d 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 animpermeable 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
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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
ReservoirsSeal (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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SeismicAmplitude
Mapof a
Horizon
Channels
Modified from Brown, 1996
3-D Seismic datadefine reservoir-quality,channel-fillsand deposits
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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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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).
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N
a b
c d
23
1
4
34 4
Well
Exercise 3
Well
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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?