PETROLEUM SYSTEM: MIGRATION & ACCUMULATION Petroleum

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

  1. Oil is generated from about 100'c
  1. 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