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PETROLEUM SYSTEM
In t roduct ion to petro leum geology
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ROCK TYPES
Magmatic (igneous) rocks- Cooling of lavas Plutonic (crystallized)
Volcanic (amorphous)
Metamorphic rocks- Transformation of existing rocks
Temperature Pressure
Sedimentary rocksDeposition on the Earths surface
Products of erosion (clastics)
Chemical precipitation (carbonates)
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SEDIMENTARY ROCKS
Petrophysical characteristics Grain : nature, shape
Inter-granular space :
Pores : void between grains
Matrix : during sedimentation
Cement : after sedimentation (diagenesis) Parameters : porosity, permeability
The Petroleum Trilogy
Source rock
Reservoir rock
Seal rock
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PETROLEUM GEOLOGY
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ORIGIN OF HYDROCARBONS
Transformation of organic matter (O.M.) from dead fauna or flora
Accumulation& Preservationof O.M.
Modificationof depositional conditions
Temperature
Pressure
Transformationof Kerogen into Hydrocarbons
Oil
Gas (Methane)
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FROM O.M. TO ACCUMULATION
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ACCUMULATION & PRESERVATION OF O.M.
Deposition & Accumulation
Origin of O.M. Living organisms (animals, plants)
Continental areas, aquatic areas (lakes, seas)
No destruction before deposition (quick burial)
PreservationPreservation of O.M. (conditions for future accumulation)
Fast protection against :
Bacterial destruction
Degradation by oxygen (in the air and dissolved in water)
Anoxic environment (i.e. lack of oxygen, also anaerobic)
Specific depositional conditions : anoxic environment and fine-grained sediment
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ACCUMULATION & PRESERVATION OF O.M.
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ORGANIC MATTER : SUMMARY
Preservation ordestructionof O.M. depends on:
Sediment type
Sedimentation rate
Environment (e.g. energy level)
Geological environments (quiet)
Lakes
Deltas
Marine environments
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ORIGIN AND EVOLUTION OF O.M.
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ORGANIC MATTER & KEROGEN
Different origins of O.M.> different types of Kerogen Type I : lakes (lacustrine algae)
Type II : open marine (zoo- & phyto-plankton, micro-organisms)
Type III : terrestrial vegetation (forests)
Type IV : oxidized terrestrial vegetation ( dead carbon )
Three stepsof O.M. transformation
Diagenesis (burial, lithification)
Catagenesis (formation of Kerogen) > 60C
Metagenesis > 120C
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EVOLUTION OF O.M. & KEROGEN
Diagenesis: Bacterial degradation Immature step
Catagenesis: Thermal degradation > weak chemical links breaking Oil window
Metagenesis: Thermal degradation > strong chemical CC links breaking Gas window
60C
120C
60C
120C
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THE PETROLEUM SYSTEM
The Petroleum Trilogy
Source rock
Reservoir rock
Seal rock
Structural history of the basin
Deformation of layers and creation of traps
Subsidence and maturation of O.M. in existing source rocks
Thermal gradient and pressure modeling of the basin throughout time
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SOURCE ROCK
Definition
Sedimentary rock rich in O.M.,having generated hydrocarbons
O.M. in the source rock ranges from 1 to 10%
Lithology
Very fine grained rock : shales, mudstones
Existing interbedded laminations [sediment/O.M.] > heterogeneity
Low permeability > Internal over-pressure associated with under-
compaction
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RESERVOIR ROCK
Definition : Reservoir = porous & permeable rock Porosity
Origin : primary, secondary
Type : intergranular, intragranular, cracks & fractures
Permeability
Vertical, horizontal
Quality of porosity network (grain sorting)
Influence of diagenesis : from sediment to rock (lithification)
Main factors: pressure, temperature, fluid circulation
Results: compaction, cementation, re-crystallization, dissolution
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DIAGENETIC EFFECTS
Compaction
Fluid expulsionPrecipi tat ion
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SORTING
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THE RESERVOIR TRILOGY
Porosity : volume of void in the rock ( in %)
Isolated porosity
Without connection between voids
Example : lavas
Connected porosity
Connected voids : porosity network
Example : sand
Permeability:ability for a fluid to flow through the rock (Kin milliDarcy: mD)
Different types of permeability : Vertical, Horizontal, Relative
Saturation:volume of fluid in the pores (Sin %)
Sw:for water
Shc:for hydrocarbons
Matrix
Oil
Water
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EXAMPLES
Sandstone Oolithic limestone (G)
Bioclastic limestone (W)Bioclastic limestone
EXAMP E OF POROSITY
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Thin section (~ 2 cm)
Oil impregnated
sand reservoir
Oil
blob
Water
(resin)
Grain
(quartz)
Shale
(?)
EXAMPLE OF POROSITY