1. Source Rock:
- Starts with the accumulation of organic matter (mostly microscopic marine organisms) in a sedimentary basin.
- This organic matter is buried under layers of sediment, creating an environment with low oxygen and high pressure.
2. Diagenesis:
- Over time, the pressure and heat transform the organic matter into kerogen, a solid organic material.
- This process, called diagenesis, occurs at temperatures between 50°C and 150°C.
3. Catagenesis:
- As the temperature increases further (150°C to 250°C), the kerogen transforms into oil and natural gas through a process called catagenesis.
- This happens due to the breaking down of long-chain hydrocarbons into smaller, more volatile molecules.
4. Migration:
- The newly formed oil and gas migrate through porous and permeable rock layers until they encounter a trap.
- This migration is driven by buoyancy (oil and gas are less dense than water) and pressure gradients.
5. Trap:
- A trap is a geological structure that prevents the oil and gas from escaping to the surface.
- Common traps include folds, faults, and salt domes.
6. Reservoir Rock:
- The oil and gas accumulate in a porous and permeable rock layer called a reservoir rock.
- These rocks are typically sandstone or limestone.
7. Seal Rock:
- A seal rock is an impermeable layer that prevents the oil and gas from migrating further.
- This can be shale, claystone, or salt.
In Summary:
Oil formation is a long and complicated process that involves the transformation of organic matter into hydrocarbons under specific conditions of temperature, pressure, and geological structure. The result is the accumulation of oil and gas in reservoirs, which can be extracted for human use.
