Natural gas is stored in underground porous rock formations, including oilfield gas, gas field gas, coalbed methane, mud volcanic gas, and biogenic gas, with a small amount also originating from coal seams. It is a high-quality fuel and chemical raw material. Natural gas is mainly used as fuel and can be used to manufacture 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.