1. Burial and Decomposition:
* Organic matter, mainly from marine organisms, gets buried under layers of sediment.
* As the depth and pressure increase, bacteria decompose the organic matter, releasing methane and other hydrocarbons.
2. Thermal Maturation:
* With further burial, the temperature increases.
* At temperatures between 60°C and 150°C, the remaining organic matter undergoes thermal maturation, transforming into kerogen, a waxy substance.
* This process produces more methane and other hydrocarbons, which are trapped within the kerogen.
3. Migration and Accumulation:
* The hydrocarbons migrate upwards through porous rocks, driven by pressure and buoyancy.
* They accumulate in porous rock formations, known as reservoirs, where they become trapped by impermeable layers of rock (such as shale).
4. Natural Gas Formation:
* The dominant component of natural gas is methane (CH4), with smaller amounts of other hydrocarbons like ethane, propane, and butane.
* The composition of natural gas can vary depending on the type of organic matter and the conditions of its formation.
Types of Natural Gas Formation:
* Biogenic gas: Formed at relatively low temperatures by microbial processes (bacterial decomposition).
* Thermogenic gas: Formed at higher temperatures due to thermal maturation of kerogen.
* Coalbed methane: Formed from the decomposition of organic matter in coal seams.
Key factors for natural gas formation:
* Source rock: Rich in organic matter.
* Reservoir rock: Porous and permeable to allow storage and flow of gas.
* Trap: Impermeable layers of rock that prevent gas from escaping.
* Time and temperature: Millions of years and specific temperature ranges are required for the process.
In essence, natural gas is a product of long-term geological processes that transform organic matter into hydrocarbons under high pressure and temperature. It is a valuable energy resource that plays a significant role in modern society.
