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PETROLEUM SYSTEM:MIGRATION & ACCUMULATION - Coggle Diagram
PETROLEUM SYSTEM:MIGRATION & ACCUMULATION
Oil and Gas
Oil
is liquid at STP
contains hydrocarbon numbers from 4 (butane) to as high as 40+
petroleum gas
contain hydrocarbons with carbon number from 1 (methane) to 4 (butane)
when a source rock is heated, it becomes 'mature' and generates petroleum
This is a geological cooking process
Hydrogen generation causes an increase in volume
Hydrogen-rich kerogen
abundant oil and gas
Hydrogen-poor kerogen
less hydrocarbon, mainly as gas
suitable (hydrogen-rich) fossil organic matter (kerogen) when cooked (matured) over geological time generates oil and gas (petroleum)
oil is generated from about 100°C
gas is generated from about 160°C
generation of non-hydrocarbon gases
H2S
catagenesis of S-rich kerogen
microbial sulphate reduction
thermochemical sulphate reduction
CO2
catagenesis of kerogen
thermal decomposition of carbonate
oxidation of hydrocarbon
N2
(late) catagenesis of kerogen
concentration as inert residue
Migration & Accumulation
the oil will move from sources rock to reservoir to accumulate there.
migration is controlled by physical properties of sedimentary strata (oil moving through permeability, porosity)
the driving forces is pressure
Primary Migration
the movement of oil and gas out of the fine-grained sources rocks into the coarse-grained reservoir rocks.
the distance of primary migration in fine-grained is usually short only as far as needed to reach a permeable bed
transport mechanisms are believed to carry most of hydrocarbons
diffusion.
molecular solution oil-phase and gas-phase migration.
Secondary Migration
driven by buoyancy, limited by permeability and fluid viscosity
initial pathway dendritic until 'path of least resistance' established
follows path of maximum rising until barriers are met
possibilities of mixing (later generated oil, gas, other sources kitchen)
possibilities of physical, chemical and bacterial alterations (interactions with water, minerals, gases)
Emplacement
development of advancing petroleum 'front'
water displacement, initially in most porous/permeable increase in petroleum filled pores
invasion of least porous/ permeable zones.
limits of cap rock seal capability
Possibilities of gas displacement, leakage (paleo-oil legs).
Mixing and homogenization over geological time
Tertiary Migration
movement of oil and gas formation of recognizable accumulation
movement of previously formed oil and gas accumulation, either to fresh trap or leakage to the surface