Natural Gas has been created over thousands of years through thermogenic and biogenic mechanisms. It is formed due to decaying remains of pre-historic plant and animal life. Similar to petroleum, most natural gas formation is due to the breakdown of prehistoric marine zooplankton. Zooplanktons are tiny animals found in the surface of aquatic environment. They subsist on a diet of phytoplankton (plants found in the sea), which in turn rely on the energy of the sun to produce organic matter and energy through photosynthesis.
Natural gas is a hydrocarbon gas consisting mainly of methane with varying amounts of alkanes with a small percentage of nitrogen, carbon dioxide, hydrogen sulfide and sometimes helium. Along with petroleum they are found in deep underground rock formation and form part of hydrocarbon reservoirs in coal beds and methane clathrates.
They meet a very significant percentage of the world’s energy needs along with coal and oil. They come from various sources and have evolved either through thermogenic or biogenic processes. Fossil fuels are formed when organic remains of animals and plants are suppressed beneath the earth’s surface under extreme heat and pressure. Over a long period of time, they are covered with mud and sediments which break down the carbon bonds in the organic matter. At relatively lower temperature in shallower deposits, more oil is produced as compared to natural gas. At deeper deposits where temperature is higher, more natural gas is found than oil. Natural gas which is extracted from such sources is referred to as thermogenic natural gas. On the other hand, natural gas formed due to the transformation of organic matter by tiny micro-organisms is referred to biogenic natural gas. Let us examine them in a bit more detail in the ensuing paragraphs.
Thermogenic natural gas substance
Thermogenic natural gas originates from fine grain rock formation typically 3000 feet underground. Common sources of thermogenic natural gas include shale, coalbed, tight limestone etc. It is a result of chemical reactions that occur without the presence of micro-organisms. These decomposition reactions are triggered by the application of extreme heat and pressure underground. This gas contains a large percentage of non-methane hydrocarbons and forms a significant portion of natural gas production and reserves worldwide. In conventional hydrocarbon formation, traditional and standard drilling procedures can be adopted to extract them. However when the source rocks have limited permeability and are inaccessible, sophisticated drilling procedures such as fracking have to be adopted so as to bring them to the surface. Most of the natural gas extraction and production comes through this conventional gas formation.
How biogenic gases are formed?
Natural gas which is produced by methanogenic organisms is called biogenic gas. Methanogens are tiny methane producing mechanisms which chemically break down organic matter to produce methane. They are found in marshes, bog, landfills and shallow sediments. Formation of methane through biogenic process takes place closer to the earth’s surface with majority of it getting lost in the atmosphere; however, some of them can be trapped underground. Methanogenic archaea is responsible for all biological forms of methane. As these methanogens live and grow, methane accumulates in their underground habitat. This biogenic natural gas is composed almost purely of methane and can be found in bodies of fine grained sediment at depths of 10-300 feet underground.
It is interesting to note that the delicate balancing of earth’s radiation and moisture in atmosphere is taken care by biogenic gases. The biogases include oxygen, nitrogen, carbon dioxide, carbon monoxide, methane, ozone, nitrogen dioxide, nitric acid, ammonia, hydrogen and carbonyl sulfide and other complex non-methane substances. Unfortunately all of the above gases fall under the greenhouse category with the exception of oxygen and nitrogen. Hence, this poses a challenge for extractors.
The principal source of biogenic gas containing methane are landfill gas, biogas and methane hydrate.
Natural gas formed due to anaerobic decay of non-fossil organic matter (biomass) through anaerobic digester or fermentation is referred to as biogas. It is a form of renewable energy and can be produced from wide range of organic feedstock such as biomass, agricultural waste, certain industrial wastes, municipal waste, sewage plants etc.
A classic example of biogenic methane is landfill gas. It forms part of biogas. Waste containing landfills usually have significant amount of natural gas due to decomposition of the waste materials. Excluding water vapor, about half of landfill gas is methane. These landfills also contain small amounts of carbon dioxide, nitrogen, oxygen, hydrogen and small traces of hydrogen sulfide and siloxanes. If the gas is not removed, the pressure may increase significantly and work its way to the surface. This can result in significant damage to the landfill structure, cause a pungent odor and also sometimes cause an explosion. The gas has to be vented to the atmosphere, flared or burned to generate electricity. Landfills are designated locations for disposal of waste collected from residential, industrial, and commercial entities and are the third largest source of human-related methane emissions in the United States. It is important to note that landfill gas cannot be transported in utility natural gas pipelines as the carbon dioxide levels need to be reduced significantly.
Methane Hydrates are ice-like structures in which molecules of methane are trapped. The chief constituent of methane hydrates is natural gas. They are found either in ocean floor or in Arctic permafrost. Methane that forms the hydrate can be of biogenic origin caused due to biological activity of sediments in the ocean floor or thermogenic origin caused due to geological activity deep within the earth. Some estimates put the reserves of energy found in methane hydrates exceeding that of other fossil fuels put together. However the development and commercial exploitation is still in the nascent stage due to environmental considerations.
Supply Chain scenario and conclusion
Thermogenic gas supplies have an established supply chain global network while biogenic gases have localized supply chain distribution network from storage, transport and consumption perspective. Most of the biogenic gases are consumed at the domestic level with a confined infrastructure and hence unlike thermogenic gases they do not require extensive transportation and distribution efforts. Also, most of the biogenic facilities are intended for captive consumption and so they do not come under the regulated or organized market environment. However, the role played by biogenic gases is significant in meeting the energy needs of unorganized market segments.