Natural gas is stored in underground porous rock formations, including oil field gas, gas field gas, coal bed methane, mud volcanic gas and biogenic gas, etc., and a small amount is also derived from coal seams. It is a high-quality fuel and chemical raw material. The main purpose of natural gas is as fuel, which can be used to produce carbon black, chemicals and liquefied petroleum gas. Propane and butane produced from natural gas are important raw materials for modern industry. Natural gas is mainly composed of a mixture of gaseous low-molecular hydrocarbons and non-hydrocarbon gases.