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