How is natural gas formed?
As a fossil fuel, natural gas is formed from the decaying remains of pre-historic plant and animal life. As with petroleum, most natural gas formation is due to the breakdown of prehistoric marine zooplankton. Zooplankton subsist on a diet of phytoplankton, which, in turn, rely upon the energy of the sun to produce organic matter and energy through photosynthesis.
We can think of gas (or oil or coal for that matter) as organic material that is prevented from complete decay. Typically, it will be found at the top of petroleum reservoirs, where it has been formed by the combined action of methanogenic bacteria (they produce methane while they decompose organic material) and through catagenesis (the thermal decomposition of kerogen).
As marine sediments are buried deep within the earth, high temperatures and pressures lead to varying degrees of the completion of catagenesis, which is the process that produces both petroleum and natural gas. Higher temperatures and pressures favor the formation of lighter hydrocarbons (natural gas), and so oil/gas formations that are deeper in the earth tend to have a greater ratio of gas to petroleum.
Following the production of natural gas through the processes of diagenesis and catagenesis, the newly formed natural gas will attempt to migrate to a new location. Because the earth is filled entirely by layers of solid (or at significant depths) molten rock, the gas it contains cannot exist within a self-contained “lake”, but must decide to live within the small fraction of space (or pores) that exist in these rocks. Like the sponge in your kitchen sink (albeit, less spongy and a bit heavier) certain kinds of rock (mainly sandstone and limestone) contain pores large enough and with enough connections to serve as storage and migration sites for gas or oil or water or any other fluid wishing to call them home.
Because the light hydrocarbons that comprise natural gas are lighter than water and rock, those that exist within the earth will tend to migrate upwards until they reach the surface, or are trapped by an impermeable layer of rock.
Methane is also produced by bacteria (methanogens) that decompose organic matter under anoxic conditions, referred to as biogenic methane. These microorganisms are active in the intestines of most animals, and are responsible for methane release from decomposing landfill waste. In the process of petroleum formation, methane may be formed in this manner during the early stages burial.
A large supply of methane is also present within coal seams, where it is found adsorbed to the structure of the coal; where it was formed by methanogenic bacteria during the decomposition process and also during catagenesis of the forming coal. “Coalbed methane” is found to lack the presence of heavier hydrocarbons (as in hydrocarbon reservoirs) and also sulfur compounds (thus the name “sweet gas”). This methane is in a near liquid state lining the pores of the coal, and is partially released when pressure in the reservoir declines due to the presence of a withdrawal well.
Uses of Natural Gas
Natural gas is a versatile, clean-burning, and efficient fuel that is used in a wide variety of applications.
In the 19th and early 20th centuries, natural gas was used primarily for street and building lighting, providing what was known as gaslight. Today, improved distribution of gas has made possible a wide variety of uses in homes, businesses, factories, and power plants.
Today natural gas is used to generate electricity which is use for powering household electronic gadgets, industrial machines, hospital equipment used for preservation purposes and lighting up a nation.
Natural gas is also used for cooking in our modern world. Natural gas for this purpose is stored in air-tight metallic cylinders which are connected to gas cookers with a hose through which the gas pass into the cooker and burns as fire.