Petroleum system: Migration & Accumulation

Migration

Definition :Movement of petroleum from source rock toward a reservoir

Principle : Move at different phases (buoyancy), rate of migration is controlled by properties of reservoir & carrier beds.

Constraints : Physical conditions such as T & P, permeability, capillarity, surface tension, molecular size & density. Chemical property is solubility of migrating hydrocarbons

Stages

Primary : Process of losing hydrocarbons from the source rock.

Tertiary : Migration to the surface, either from a reservoir or source rock (Dismigration).

Secondary : Migration from source to reservoir which includes migration within the reservoir rock itself.

Accumulation

Elements necessary for hydrocarbon accumulation

Reservoir Rock

Source Rock

Seal

Thermal History

Migration & trapping of hydrocarbon

Geological History

Structural History

Depth of burial

Gross thickness range

Sedimentary rock types

Outcrop occurences

Lateral continuity

Age

Thickness

Kerogen type

Depth of burial

Vertical / lateral seals

Lithology of potential seals

Presence of evaporites

Fracture system

Rates of burial

Rates of deposition

Paleogeothermal gradient

Tectonic history

Fractures

Controls of migration

Permeability & porosity

Controls on migration

Main tectonic events

Episodes of subsidence

Unconformities

Paleotopography

Dip domains

Strike & dip trends

Major faults & minor faults

Basin boundary faults

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From fine-grained source rock to course-grained reservoir rock

Expulsion is upward expect when there is over pressure

Source rock to carrier bed

Carrier to bed

Movement of fluids within reservoir rocks leading to oil & gas seggregation

Possibility of mixing (Interactions between oil, gas and water)

Higher permeability, higher migration

Petroleum moves through continuous sands, fractures, faults & unconformities until caprock is encountered

Petroleum moves into a new carrier

Leakage, seepage, dissipation & alteration of petroleum as it reaches the Earth's surface

Emplacement

Possibilities of gas displacement & leakage

Mixing & homogenization over geologic time

Disturb the composition