Composition and origin of natural gas

Natural gas is a gaseous hydrocarbon mix consisting principally of methane (CH4) usually over 80% v/ve and in lower quantities of ethane (C2H6), propane (C3H8), butane (C4H10) and pentane (C5H12). It also contains carbon dioxide (CO2), hydrogen sulfide (H2S)  and nitrogen (N2) in low contents.  

Methane is a light, cοlorless, odorless and non toxic gas which is artificially odored after its production in order to be detectable in case of leakage. As it is lighter than air, in the case of leakage, it moves upwards in the air where it is diluted and becomes harmless. 

Natural gas is derived, under conditions of high pressure and temperature in considerable depth underground, from the thermal dissolution of the initial high-molecular weight organic matter which originates from organic sediments (terrestrial or marine). The methane produced under such conditions is trapped into imprevious geological formations creating gas deposits on the bottom of which it is very common to also find trapped oil. 

Natural gas produced from different reservoirs may differ in composition, since the composition of the gas is related to its origin and the species of the organic matter from which it has been formed.