The composition of natural gas changes according to the production field, the production process, the conditioning, the processing and the transportation.
Natural gas is found in the subsoil in accumulations in porous rocks that are isolated from the exterior by impermeable rocks and may be related or not to oil deposits. It is the outcome of the aerobical degradation of organic matter that comes from extraordinary amounts of microorganisms that were accumulated by the sea coast in prehistoric times. This organic matter was unburied from great depths. Therefore, its degradation occurred without contact with air, at high temperatures and under high pressure.
Natural gas has a methane content over 70% of its composition, density lower than 1 (lighter than air) and a higher heating value between 8,000 and 10,000 kcal/ m3, depending on the content of heavies, namely ethanol and propane, and inerts, namely nitrogen and carbon gas.
Natural gas is one of the main primary energy sources and in 2009 it was responsible for 24% of the primary energy consumption in the world.