basic geology principles for ioil exploration

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Basic Geology
for Oil
Exploration
Basic Geology
for Oil
Exploration

2. Geoscience Training Center
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GENERALITIES
SEDIMENTARY ROCKS
SOURCE ROCKS
RESERVOIRS AND SEALS
HYDROCARBON TRAPS AND MIGRATION
PETROLEUM SYSTEM
SummarySummarySummary

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Earth componentsEarth components
Atmosphere
Crust
Mantle
Core
Inner Core

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Earth crust componentsEarth crust components
46,6
27,72
8,13
5 3,63 2,83 2,59 2,09 1,41
0
5
10
15
20
25
30
35
40
45
50
O Si Al Fe Ca Na K Mg Other
%

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Rock- mineral componentsRock- mineral components
Silica (SiO2)
Quartz
Silicates (SiO4 + Al, Ca, Na, K, Mg …)
Feldspars
Amphiboles and pyroxenes
Micas
SILICA AND SILICATES

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Calcium Sulphate (Anhydrite, Gypsum)
Chlorides (Halite, Sylvite)
EVAPORITE MINERALS
Sulphides, Oxides, phosphates …
OTHERS
Calcite (CaCO3)
Dolomites (Mg, Ca(CO3)2 )
CARBONATES
Rock- mineral conponentsRock- mineral conponents

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Earth crust rocksEarth crust rocks
MAGMATIC ROCKS
Formed by cooling and crystallization of magma
MAGMATIC ROCKS
Formed by cooling and crystallization of magma
SEDIMENTARY ROCKS
Formed in surface by mechanical, chemical or
biochemical processes, then buried at moderate depth
SEDIMENTARY ROCKS
Formed in surface by mechanical, chemical or
biochemical processes, then buried at moderate depth
METAMORPHIC ROCKS
Formed by transformation of magmatic or
sedimentary rocks
METAMORPHIC ROCKS
Formed by transformation of magmatic or
sedimentary rocks

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Rock cycleRock cycle
MAGMATIC ROCKS
METAMORPHIC
ROCKS
SEDIMENTARY
ROCKS
Fusion
Erosion
Magma
Cooling and
crystallization
Solid
Transformation
SEDIMENTS
Diagenesis

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Rocks and hydrocarbonRocks and hydrocarbon
Sedimentary rocks are the only family of
rocks where hydrocarbons can occur

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LithologyLithology
Standard reprensatation of rock faciès
Sandstone
Limestone
Clay, Shale

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GENERALITIES
SEDIMENTARY ROCKS
SOURCE ROCKS
RESERVOIRS AND SEALS
HYDROCARBON TRAPS AND MIGRATION
PETROLEUM SYSTEM
SummarySummary

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Sedimentary Rocks
Characteristics
Sedimentary Rocks
Characteristics
GRAINS
Mineralogy, Granulometry, Sorting, Morphology
MATRIX
Binder (contemporaneous with sedimentation)
Cement (secondary binding material), Mineralogy
PORES (Void space)
Porosity (percentage of void volum), type of porosity
Effective porosity (interconnected voids)
Permeability (ability to led a fluid circulate)

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Sedimentary Rocks
Classification
Sedimentary Rocks
Classification
CLASTIC (sandstone)
CARBONATE (limestones, dolomite)
EVAPORITES (salt)

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Clastic RocksClastic Rocks
Grain size
Lutites Arenites Rudites
Sands
VeryFine
Fine
Medium
Coarse
VeryCoarse
Granules
Gravel
Pebbles
Clay Silt
Mudstone Siltstone Sandstone Conglomerats
LooseConsodilated

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Clastic Rocks formationClastic Rocks formation

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Carbonates RocksCarbonates Rocks
J. Guillemot 1988
Limestone Dunham’s Classification

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Carbonates Rocks formationCarbonates Rocks formation
Chemical precipitation or Biochemical formation

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Evaporites RocksEvaporites Rocks
ContinentalCoastalSubaqueous
Sulfate Salt
Continental sebkha
Coastal sebkha
Crystalline,
laminated,Turbidites
Displacive Halite
Chevron Halite

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Evaporites Rocks formationEvaporites Rocks formation

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Sediment diagenesisSediment diagenesis
Sediments
(loose)
Sedimentary
Rocks
(Consolidated)
Pressure, Temperature
Water circulation, biological factors
Ex : Sand Sandstones
Progressive transformation
Consequence of burial (subsidence)

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Margin typesMargin types
Geological Society of America

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Margin typesMargin types
M. T. Halbouty in AAPG mem. 40, 1986

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Sedimentary Bassin exempleSedimentary Bassin exemple
A. Perrodon and J. Zabeck, 1990
Paris Bassin

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GENERALITIES
SEDIMENTARY ROCKS
SOURCE ROCKS
RESERVOIRS AND SEALS
HYDROCARBON TRAPS AND MIGRATION
PETROLEUM SYSTEM
SummarySummary

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Source Rock - DefinitionSource Rock - Definition
Rock Containing a few pourcentage
of organic matter which eventually
be transformed in hydrocarbon

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Kerogen typesKerogen types
TYPE I :
TYPE II :
TYPE III :
From lacustrine algae
From marine zoo or phyto plancton
From continental plants

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Diagenesis
Ro = 0.5%
Ro = 2.0%
Catagenesis
60° to 120°
2 to 4 km
depth
Metagenesis
KK44
KK33
KK22
KK11
KK
KK
Oil Phase-
Out
OilOil GasGas
OilOil GasGas
OilOil GasGas
ConCon GasGas
GasGas
Hydrogen rates
Kerogen
Onset of Oil
Generation
Horsfield and Rullkotter, 1994
Burial to
Greater and
Hotter
Depths
Source Rocks- MaturationSource Rocks- Maturation

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During burial, Temperatures and pressures rise.
Chemical reactions generates the liquid and gas
hydrocarbons found in the source rocks
Catagenesis / MetagenesisCatagenesis / Metagenesis
CATAGENESIS = generation of oil = OIL WINDOW
METAGENESIS = generation of gas = GAS WINDOW

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Organic-rich
Source Rock
Thermally Matured
Organic Matter Oil
The Origin of PetroleumThe Origin of Petroleum

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GENERALITIES
SEDIMENTARY ROCKS
SOURCE ROCKS
RESERVOIRS AND SEALS
HYDROCARBON TRAPS AND MIGRATION
PETROLEUM SYSTEM
SummarySummary

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A rock in which oil and gas accumulates
Two main types :
- clastic rocks
- carbonate rocks
Reservoir rocks - DefinitionReservoir rocks - Definition

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Porosity : space between rock grains
in which oil accumulates
Permeability : passage-ways between
pores through which oil and gas moves
Saturation : ratio of fluid volume by
pore volume
Porosity : space between rock grains
in which oil accumulates
Permeability : passage-ways between
pores through which oil and gas moves
Saturation : ratio of fluid volume by
pore volume
Reservoir rocks - characteristicsReservoir rocks - characteristics

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Good Porosity = Lots of Space for Petroleum
Pores
(blue)
Porosity influencePorosity influence

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Pore-Filling Cement Reduces Quality
= Less Space for Petroleum
Cement
(pink)
Cement influenceCement influence

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A rock through which oil and gas cannot move
effectively (Non-permeable rocks)
Most common lithologies :
Shales
Saline rocks
Possibly very compact sandstone or limestone
(with no porosity)
Seal rocks - DefinitionSeal rocks - Definition

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GENERALITIES
SEDIMENTARY ROCKS
SOURCE ROCKS
RESERVOIRS AND SEALS
HYDROCARBON TRAPS AND MIGRATION
PETROLEUM SYSTEM
SummarySummary

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Secondary MigrationSecondary Migration
hydrocarbons move through a permeable rocks
toward the earth’surface
= SECONDARY MIGRATION

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Migration and trappingMigration and trapping
Migrating hydrocarbons may encounter an
impermeable layer before reaching earth’surface
= TRAPPING (Accumulation)

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Structure visible at the surface Seepage
Structural Traps Stratigraphic Traps
+ + + +
+ + + +
Crystalline basement of substratum of the sedimentary sequence
1 Anticlinal
1
1
1
2 Horst
2
3 Flank if salt or shale dome
3
3
3
3
3
6 Erosional pinch-out
6
6
7 Lens (sand or sandstone)
7
4 Trap against fault
4
5 Sedimentary pinch-out
5
8 Reef
8
TrapsTraps

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American Petroleum Institute, 1986
Salt Dome
Fault
Unconformity
Pinchout
Anticline
Hydrocarbon Trap examplesHydrocarbon Trap examples

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2480
120° F120° F
350° F350° F
GenerationGeneration
MigrationMigration
Seal RockSeal Rock
Reservoir
Rock
Reservoir
Rock
OilOil
WaterWater
Gas
Cap
Gas
Cap
EntrapmentEntrapmentAccumulationAccumulation
Source
Rock
Source
Rock
SynthesisSynthesis

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• Largest NorthAmerican field
• More than 8 billion barrels recoverable
• Largest NorthAmerican field
• More than 8 billion barrels recoverable
Barrow
Arch
Barrow
Arch
Sea LevelSea Level
10,00010,000
20,00020,000
30,00030,000
Brooks
Range
Beaufort
Sea
Seal
ReservoirReservoir
KitchenKitchen
AnticlinalTrapAnticlinalTrap
120°F
unconformityunconformity
SouthSouth NorthNorth
American Association of Petroleum Geologists, 1990
Prudhoe Bay Oil Field (1968)Prudhoe Bay Oil Field (1968)
Anticlinal/Unconformity
Combination Trap

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•Largest “lower-48” field
•More than 5 billion barrels recoverable
•Largest “lower-48” field
•More than 5 billion barrels recoverable
Sea LevelSea Level
1,0001,000
2,0002,000
3,0003,000
120°F
Seal
ReservoirReservoir
KitchenKitchen
UnconformityTrapUnconformityTrap
unconformityunconformity
WestWest EastEast
Seal
American Association of Petroleum Geologists, 1990
East Texas Oil Field (1930)East Texas Oil Field (1930)

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In Situ PhasesIn Situ Phases

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ConclusionConclusion
CONDITION FOR HC ACCUMULATION
Presence of a source rock which must be mature
Presence of reservoir rocks
Presence of seals
Presence of traps
Adequate timing between trap formation and
Hydrocarbons generation and formation
Adequate timing between trap formation and
Hydrocarbons generation and formation

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GENERALITIES
SEDIMENTARY ROCKS
SOURCE ROCKS
RESERVOIRS AND SEALS
HYDROCARBON TRAPS AND MIGRATION
PETROLEUM SYSTEM
SummarySummary

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Petroleum system - descriptionPetroleum system - description
Source Rock
(+ organic matter)
Maturation
(burial)
+
=
Generating
Sub-system
Reservoir
Seal
Trap
+
=
Trapping
Sub-system
Migration

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Petroleum system - timingPetroleum system - timing
Depth(z)
Temperature
T0
T = T0 + g.zDiagenesisCatagenesisMetagenesis
Dry Gas
Zone
1 - Primary Migration
2 - Secondary Migration
3 - Dismigration
Immature
Zone
Oil Zone
Wet Gas Zone

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Teapot
Owens
Pod of
Active
Source
Rock
Just
Big Oil
Hardy Lucky
Immature Source
Rock
Raven
Marginal
250 Ma
A A’
Critical MomentCritical Moment
Magoon and Dow, 1994
ReservoirRock
David
Deer-Boar Petroleum SystemDeer-Boar Petroleum System
Zero Edge of
Reservoir
Rock

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Overburden
Seal
Reservoir
Source
STRATIGRAPHIC
EXTENT OF
PETROLEUM SYSTEM
Trap Trap
Essential
elements of
petroleum
system
POD OF ACTIVE
SOURCE ROCK
Basem
ent
Underburden
Sedimentary
basin-fill
GEOGRAPHIC EXTENT OF PETROLEUM SYSTEM
250 MaTrap
Petroleum accumulation
Top of oil window
Bottom of oil window
Location for burial history chart
A A’
Magoon and Dow, 1994
Critical Moment = Time of Expulsion/MigrationCritical Moment = Time of Expulsion/Migration
Petroleum System at Critical MomentPetroleum System at Critical Moment

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Basement
GEOGRAPHIC EXTENT OF PETROLEUM SYSTEM
Present-Day
STRATIGRAPHIC
EXTENT OF
PETROLEUM SYSTEM
Petroleum accumulation
Top of oil window
Bottom of oil window
Trap TrapTrap
Seal
Reservoir
Source
Underburden
Overburden
A A’
Magoon and Dow, 1994
Present-Day Petroleum SystemPresent-Day Petroleum System

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400 300 200 100
Paleozoic Mesozoic Cen.
P NKJTPMD P
Lithology
Rock
Unit
Depth(Km)
Source
Reservoir
Seal
Overburden
1
2
3
Placer Fm
George Sh
Boar Ss
Deer Sh
Elk Fm
Top gas window
Critical MomentCritical Moment
Thick
Fm
R
Magoon and Dow, 1994
GenerationGeneration
Time of Expulsion and Migration. (Trap must already exist)
Top oil window
Burial History ChartBurial History Chart

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Magoon and Dow, 1994
Inventory of AccumulationsInventory of Accumulations
Field
Name
Date
discovered
Reservoir
rock
API
Gravity
( API)
Cumulative oil
production
(x10 bbl)
Remaining
reserves
(x10 bbl)
Hardy
Lucky
Marginal
Teapot
1989
1990
1990
1992
Boar Ss
Boar Ss
Boar Ss
Boar Ss
29
15
18
21
85
5
12
9
Big oil
Raven
Owens
Just
1954
1956
1959
1966
Boar Ss
Boar Ss
Boar Ss
Boar Ss
32
31
33
34
310
120
110
160
90
12
19
36
89
70
65
34
o 6 6
Deer-Boar Petroleum SystemDeerDeer--Boar Petroleum SystemBoar Petroleum System

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1 2
400 300 200 100
Paleozoic Mesozoic Cenozoic
D M P P TR J K Pε N
Geologic
Time-Scale
Petroleum
System
Events
Source Rock
Reservoir Rock
Seal Rock
Overburden
Trap Formation
Generation, Migration,
and Accumulation
Preservation
Critical Moment1. Western North Slope
2. East-central North Slope
Bird, 1994
North Slope, Alaska
Petroleum System Events ChartPetroleum System Events Chart

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Spill PointSpill Point
Spill PointSpill Point
Seal RockSeal Rock
(Mudstone)(Mudstone)Reservoir RockReservoir Rock
(Sandstone)(Sandstone)Migration fromMigration from
‘Kitchen’‘Kitchen’
1) Early Generation
2) Late Generation
Gas displaces allGas displaces all
oiloil
Gas beginning toGas beginning to
displace oildisplace oil
Displaced oilDisplaced oil
accumulatesaccumulates
Petroleum SystemPetroleum SystemPetroleum System