Natural gas is a non-toxic, colorless and odorless compound, made up of a mixture of hydrocarbons in which its main component is methane (CH4), a simple molecule made up of 1 carbon atom and 4 hydrogen atoms.
Its chemical composition, however, varies significantly depending on its origin, since it is usually associated with other molecules or elements such as hydrogen sulfide (H2S), carbon dioxide (CO2), nitrogen (N2) or helium (He) which is extracted when natural gas is used for industrial and domestic uses.
The origin of natural gas, like oil, can be found in the decomposition processes of organic matter, which took place between 240 and 70 million years ago, during the time when large reptiles and dinosaurs inhabited the earth. planet (Mesozoic Era). This organic matter came from planktonic organisms that accumulated on the seabed of coastal platforms or in the shallow basins of ponds, and which were buried under successive layers of earth by the action of natural phenomena.
Thus, its fundamental compounds –fats and proteins– decomposed very slowly in the absence of oxygen due to bacterial action.
The gases generated, due to pressure differences, ascended through the porous rocks of the earth's crust until they reached layers of impermeable terrain, under which they were trapped, originating the large pockets or deposits from which humans today take advantage.
This process is, saving the distances, similar to the one that takes place in the landfills where we throw away the rubbish. The organic matter that comes from the remains of fruit, vegetables or meat, for example, when it decomposes, produces a gas with characteristics similar to natural gas, which must be evacuated from the landfill to the atmosphere, through a network of drainage pipes to prevent the emissions from causing an explosion, or be stored and used as fuel: it is the so-called biogas.
In a reservoir, the less heavy gas occupies the upper part of the cavity, the oil the intermediate part, and in the lower part we normally find salty water (which is why it is believed that it originated from the seabed). At high pressures, the gas mixes with oil –associated natural gas– or dissolves, although we can also find it alone, in bags other than those of oil. The strata under which the gas pockets accumulate are made up of impermeable rocks. The accumulation depends on factors such as the porosity of the rock, the volume of gas and the capacity of the bag.