1. Organic Matter Accumulation: Tiny marine organisms (plankton, algae) die and settle to the bottom of oceans and lakes. Over time, layers of sediment build up, burying the organic matter.
2. Burial and Heat: As more sediment accumulates, the pressure and temperature increase. This transforms the organic matter into kerogen, a waxy solid.
3. Thermal Cracking: With increasing depth and temperature, the kerogen breaks down into hydrocarbons, including natural gas (primarily methane). This process is called thermal cracking.
4. Migration and Accumulation: The natural gas, being lighter than water, migrates upward through porous and permeable rock formations. It eventually gets trapped in a geological structure called a reservoir rock, often capped by an impermeable layer, preventing further migration.
Key factors for natural gas formation:
* Source rock: The rock containing the original organic matter.
* Reservoir rock: Porous and permeable rock that holds the natural gas.
* Trap: A geological structure that prevents the natural gas from escaping.
* Time and temperature: The process takes millions of years and requires specific temperature and pressure conditions.
Types of Natural Gas Deposits:
* Conventional gas: Found in reservoirs with a conventional trap, often associated with oil.
* Unconventional gas: Found in unconventional formations like shale, tight sandstone, or coal seams, requiring specialized extraction techniques.
Therefore, natural gas is formed from the decay of ancient organic matter under specific geological conditions, resulting in a complex and lengthy process.
