PETROLEUM SYSTEM: MIGRATION & ACCUMULATION
Oil and gas migration
The migration of oil and gas happened in three stages which are the primary migration, secondary migration and tertiary migration
At primary migration, the hydrocarbon is being expulsion from the fine-grained source rocks to the coarse-grained reservoir rocks
At secondary migration, the hydrocarbon is moving from the fine-grained rock source to the coarse-grained rock source through porosity and permeable reservoir or trap the result of buoyant and hydrodynamic processes
Oil and gas accumulation
The oil and gas will accumulate at the source rock which it can penetrate and trap in a large area by the migration stages.
OIl is a liquid at STP and contains hydrocarbons with carbon numbers ranging from butane which is 4 to high,
Petroleum gas contains hydrocarbons with carbon numbers from methane to butane
Hydrogen-rich kerogen yields abudant oil and gas while Hydrogen-poor kerogen yields less hydrocarbon
Geological cooking process
When a source of rock is heated, it become mature and generates petroleum
When we heated oil shale, it will produce oil through condenser
When we heated coal, it will go through condenser by coal tar to produce gas
Mass balance considerations: from kerogen to cooked kerogen by maturation process of heat and time
Suitable (hydrogen-rich) fossil organic matter (kerogen) when cooked (matured) over geological time generates oil and gas
- Oil is generated from about 100'c
- Gas is generated from about 160'C
Areas of mature source rock are often called kitchens
Generation of non-hydrocarbon gases
H2S- Catagenesis of S-rich kerogen and microbial sulphate reduction
CO2- Catagenesis of kerogen and thermal decomposition of carbonate
N2- Catagenesis of kerogen and concentration as inert residue
Deposits are converted to oil must from the source rock to the reservoir to accumulate
Migration is controlled by the physical properties of the sedimentary strata that the oil is moving through permeability and porosity driven by pressure
Deposits are converted to oil must from the source rock to the reservoir to accumulate
At tertiary migration is the movement of oil and gas after formation of recognizable accumulation. It include leakage, seepage, dissipation and alteration of petroleum as it reaches the earth's surface