What is Natural Gas?
Natural gas is a colorless, odorless gas in its pure form. It consists mainly of methane gas; it can also include ethane, propane, butane and pentane. Below is a chart outlining the typical constituents of natural gas before it is refined.
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Typical Composition of Natural Gas
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Methane
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CH4
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70-90%
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Ethane
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C2H6
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0-20%
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Propane
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C3H8
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Butane
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C4H10
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Carbon Dioxide
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CO2
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0-8%
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Oxygen
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O2
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0-0.2%
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Nitrogen
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N2
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0-5%
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Hydrogen sulphide
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H2S
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0-5%
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Rare gases
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A, He, Ne, Xe
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trace
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Methane is a molecule consisting of four (4) hydrogen atoms and one carbon atom (CH4).
Natural gas is considered ‘dry’ when it is almost pure methane, after having most of its associated hydrocarbons removed. When the other hydrocarbons are present it is considered ‘wet’.
Natural gas has many uses; residential, commercial and industrial. It is found in reservoirs both on land and undersea (seabed), and is mostly associated with oil deposits. Deposits of oil and gas are determined by conducting seismic surveys in locations where the deposits are present. Once brought from underground, the gas is refined to remove impurities such as sand, water, and other gases. Some of the other hydrocarbons, including propane and butane are removed and sold separately. Hydrogen sulphide is one other impurity that is removed and can be refined to produce sulphur. After being refined, natural gas is transmitted through pipelines to its point of use.
The Formation of Natural Gas
Natural Gas is a fossil fuel like oil and coal. Fossil fuels are the remains of plants and animals and micro-organisms that lived millions of years ago. Natural gas is also formed by the transformation of organic matter by tiny micro-organisms. This type of gas is referred to as biogenic methane. Methanogens, tiny methane producing microorganisms, chemically break down organic matter to produce methane. These microorganisms are commonly found in areas near the surface of the earth that are void of oxygen. Formation of methane in this manner usually takes place close to the surface of the earth, and the methane produced is usually lost into the atmosphere. In certain circumstances, however, this methane can be trapped underground, recoverable as natural gas.
Natural Gas Beneath the Earth
Although there are several ways that methane, and thus natural gas, may be formed, it is usually found underneath the surface of the earth. Natural gas has a low density, and once formed it will rise towards the surface of the earth usually through loose, shale type rock and other material. This methane will rise up into geological formations that 'trap' the gas under the ground. These formations are made up of layers of porous, sedimentary rock (similar to a sponge, that absorbs the gas), with a denser, impermeable layer of rock on top. This impermeable rock traps the natural gas under the ground. If these formations are large enough, they can trap a great deal of natural gas underground, in what is known as a reservoir.