Role of Natural Gas in Energy Transition Diya Handa (Year 12, Anderson)
Natural gas is a fossil energy source that is found beneath the surface of the Earth; consisting of multiple compounds, such as methane, carbon dioxide, water vapour and other natural gas liquids (NGL). It is considered to be the cleanest fossil fuel. Additionally, natural gas is odourless and colourless. When burned, it releases carbon dioxide, water vapour and a minimal amount of nitrogen oxides.
HOW IS NATURAL GAS FORMED? Natural gas was formed from plants, animals and microorganisms millions of years ago; it is formed underground due to the intense conditions. The organic matter from the decomposition of plants, animals and microorganisms is formed on layers of soil, sediment and rocks. As organic matter decays and becomes more rooted into the Earth’s crust, the temperature gets higher. These conditions of high compression and temperature cause the carbon bonds in the organic matter to break, causing the release of thermogenic methane: natural gas. Methane (CH4) is Earth’s most abundant organic compound and is made up of hydrogen and carbon. It does not necessarily have to be formed underground; instead, it can also be formed by microscopic organisms - methanogens. Methanogens are present in the intestine of mammals, and low oxygen areas near the surface of the Earth. The process of methanogens creating natural gas is known as methanogenesis. Most biogenic methane escapes into the atmosphere as gas rises through permeable matter and dissipates into the atmosphere; however, new technology is being developed to minimise this, as biogenic methane has an impact on the global carbon ‘pool’ of supply. Most thermogenic methane rises to the surface to encounter geological formations. These formations are too impermeable for the gas to escape as they are sedimentary basins and they are prone to trapping a lot of natural gas. To access this natural gas, holes need to be drilled through the rock to allow the gas to escape and be harvested. You can contain this methane to harvest it into a potential energy source. These basins can be found worldwide, such as in the deserts of Saudi Arabia, Venezuela and the Arctic.
TYPES OF NATURAL GAS There are two main categories of natural gas: 'conventional' and 'unconventional' gas. Conventional gas is easily accessible and economically viable to extract. Unconventional gas, on the other hand, is found in places where it is not convenient nor practical to perform an extraction. Fortunately, technological advancements have made such extractions possible. Conventional gas extraction can be done using standard methods which are convenient and inexpensive as it does not require specialised extraction techniques and equipment. It is found in natural porous reservoirs that are blocked with an impermeable rock stratum which can be easily unblocked Deep natural gas is an unconventional gas located 15,000 ft below the Earth’s surface. This natural gas is trapped in layers under shale, an insoluble fine-grained sedimentary rock. Hydraulic fracturing or horizontal drilling can be carried out to extract the gas. Hydraulic fracturing involves splitting open a rock with a high-pressure stream of water then opening it with grains of sand, glass or silica, allowing the gas to flow freely out of the well. Horizontal drilling is when drilling parallels the Earth’s surface, allowing access to the gas trapped between the rocks. Another unconventional deposit of gas is Tight gas. Tight gas is found underground in impermeable rock formations, making it very hard to extract. It requires expensive and complicated methods of extraction, such as hydraulic fracturing and acidizing. Acidising is similar to hydraulic fracturing but acid instead of water is injected into natural gas deposits, dissolving the rock thus allowing the gas to escape.
90
