Natural gas occur naturally. It's happened by the sedimentation of living things in the rock, soils and sea million years ago , While that time nature has changed cause from thermal and pressure of earth surface. Until the fossil become raw oil , natural gas and coal that we use it, so we called them as fossil fuel. When the fossil getting sedimentation and transform to be a raw oil , natural gas , or coal. That's why they are contains of hydrocarbon mostly, and after you take it to burn. It will give you the same energy as when you burn woods, but the fossil fuel such as natural oil or coal give more heat.
Natural gas is a mixture of hydrocarbon and another contaminated things in gas phase. The hydrocarbon which found in the nature such as methane,ethane,propane,butane,pentane ,the others contaminated which found in natural gas are co2,hydrogensulfide,helium,nitrogen,and vapor. The natural gas known as the composition of hydrocarbon