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Origin of petroleum
Six Conditions are Needed in the Formation of Petroleum.
Formation
1. Organic Material
Organic material is composed of minute fragments of animals, plants and silt that mix with the sediments. For the rock to eventually produce petroleum, the sedimentation should be rich in organic material and subject to conditions of rapid siltification in order to avoid any oxidization.
2. Siltification
Sediments (organic materials) transform into gas, oil or petroleum during siltification. The transformed product will be different according to its depth, length of duration and the temperature the organic material has been subjected to.
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First 1,000 metres |
Formation of biogenic natural gas
(methane) produced by decomposition. |
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2,000 - 3,000 metres
Thermogenic transformation … thermal maturation.
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The organic materials are transformed into oil (petroleum) with some natural gas. |
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3,000 - 4,000 metres
Transformation through the action of increased temperature.
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There is natural gas with some condensate. |
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4,000 metres and more |
Dry natural gas (the most desirable type). |
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3. Source Rock
Rich in organic material, the source rock will transform sediments into hydrocarbons. Subsequently, because of their poor retention capacity, the hydrocarbons will attempt to migrate.
Migration
Migration
The combined movement of the subsoil and the circulation of the fluids in the rock brings about a migration of hydrocarbons. Fractured and permeable zones, as well as the presence of faults are elements favourable to the circulation of hydrocarbons towards rock reservoirs.
Traps
Once the fluids are concentrated in a space, an impermeable rock cover needs to block the migratory ascent of the petroleum or gas. The trap will either store the hydrocarbons or the fluids will again move vertically depending on their density: natural gas at the top, followed by oil, then salt water at the base (see graphics).
The earth’s crust is composed of an accumulation of tectonic plates that push and ride up over each other. This activity makes possible the discovery of ancient sea bottoms on the tops of mountains. As well, this is what forms the traps.
Discovery of a Trap
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