Petroleum System Introduction to Petroleum Geology 1parte (Maria Gutierrez)

8/11/2019 Petroleum System Introduction to Petroleum Geology 1parte (Maria Gutierrez)

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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

Petroleum System Introduction to Petroleum Geology 1parte (Maria Gutierrez)

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