Petroleum forms over millions of years from the remains of ancient marine organisms. These organisms, buried at the bottom of the sea, are covered by sediment and subjected to intense heat and pressure. This process transforms the organic matter into a liquid or gaseous form, known as crude oil and natural gas.
Here’s a more detailed breakdown:
1. Accumulation of organic matter:
Dead plants and animals, mainly marine, sink to the seafloor and accumulate.
2. Burial and Sedimentation:
Layers of sand, silt, and other sediments cover the organic matter, protecting it from oxygen and further decomposition.
3. Transformation by Heat and Pressure:
As the sediments continue to accumulate, the weight and depth create intense heat and pressure. This causes the organic matter to begin to decompose and break down into simpler hydrocarbon molecules.
4. Formation of Kerogen:
The initial product of this decomposition is kerogen, a waxy, complex hydrocarbon substance.
5. Catagenesis:
With continued heat and pressure, the kerogen transforms into crude oil and natural gas through a process called catagenesis.
6. Migration:
Once formed, the oil and gas are lighter than the surrounding water and tend to migrate upwards through porous rock layers until they encounter an impermeable barrier. This creates a reservoir, where the oil and gas can be trapped and collected.