With the depleting conventional oil and gas reserves in the world on one hand and increasing guzzling energy needs on the other, the energy industry is constantly looking out for unconventional gas sources. This has led to the discovery of shale gas, tight gas, gas hydrates, coal seam gas, etc., as alternate sources of energy.
Coal seam gas (CSG), also known as coal bed methane (CBM), coal mine methane (CMM) or coal bed gas, is a form of natural gas extracted from coal beds. It is primarily made up of methane gas and found trapped in coal seams underground in the depths of 300-1000 m surrounded by water and ground pressure. Its single largest component is methane (95%-97%). It is used for domestic cooking and heating, power generation and for industry purposes to make a wide range of products.
Coal transformation phases
It is interesting to note that the coal goes through several stages before it develops into a solid shiny substance called hard coal. The journey of coal starts from something called peats, which is nothing but the wastes of the earth and plants. Over a long period of time with the heat and burial pressure acting on the peats, they transform into various maturity levels to become tough coal at the end. Peats mature into states like lignite, sub- bituminous, bituminous and finally hard anthracite which is commonly known as coal. These stages are called ranks. Lignite and sub-bituminous coals are considered to be low rank coal while bituminous and anthracites are considered to be high rank coal. It is assessed that gaseous hydrocarbons are found in more quantities in hard coal than in soft coal like lignite.
Biogenic Vs Thermogenic CSG formation
Methane formation in the coal happens mainly in two ways, one through biogenic process and the other through thermogenic process. Biogenic process-enabled methane is produced through bacteria as they get the nutrition from the coal source and produce methane as a by-product in the course. The thermogenic process occurs as a result of chemical reaction on the coal due to high pressure and temperature over a period of time. This results in production of significant amount of methane gas.
Extraction Process of CSG
Coal seam gas is extracted using nonconventional methods such as horizontal drilling or hydraulic fracturing. It is extracted by initially drilling a well vertically through rock strata until reaching the coal seam, at this point horizontal drilling process is adopted for increased access to the methane gas trapped inside. Similar to conventional oil extraction, a vertical steel encased well is drilled to reach the coal bed. In case the water and methane gas is not flowing freely, hydraulic fracturing technique is used. In this method, sand along with chemical additives is powerfully injected on the coal cleat to create a fracture so that the trapped gas could escape through the outlet to the surface. This is also called horizontal drilling. The sand helps to expand the fractures created and enlarging them to facilitate gas extraction.
The extracted gas is processed further and taken to storage facilities. It is used for domestic and international supplies for various uses. CSG is a capital intensive process and the extraction process involves tens of thousands of gas wells, with roads, pipelines, compressor stations, wastewater dams, and other infrastructure spread over huge land area.
Water plays a major role
Since coal seams contain water and methane, water has to be pumped out of the coal seam to lower the pressure and allow the gas to flow to the surface. The amount of water pumped out depends upon the type of well/coal seams and can vary between few thousands to hundreds of thousands of liters per day. The wastewater is generally toxic, salty, containing heavy metals and radio activity materials which have to be stored in tanks or holding ponds and transported through pipelines for further treatment purposes.
The main challenge organizations face while extracting CSG is the water disposal. As stated earlier, the water pumped out during the production process is contaminated and chemically toxic in nature. Various experiments have indicated that the produced water is of very high salinity and hence the presence of high sodium content is detrimental to the environment. Studies also specify that this water is not suitable for irrigation as it endangers the quality of soil in the long run and this could affect the crop growth.
Handling of water disposal is an important part of the CSG project. In the initial days, the water was channeled into the stream ways to be flushed into the ocean. But continued use of this stream channels resulted in contamination of channel ways and hence environmentalists raised their concern on the same. In recent times, the water is collected in a place called “infiltration pond” where it is treated further to eliminate the salinity. Once the water meets with the accepted levels of quality from all perspective, it is channeled into the stream.
Another key challenge in extracting CSG is that methane is a greenhouse gas and has the potential of releasing carbon dioxide in the environment. This can have adverse effect on the climate change and global warming. Organizations put a lot of effort in keeping the impact of greenhouse emissions to the minimum or acceptable levels.
World Production and reserves
Major producers of CSG are USA, Canada, Australia, UK, Kazakhstan, India etc. CSG extraction and production was pioneered by the USA in the 1970s when it started encouraging extraction of unconventional sources of natural gas. Australia which is one of the major explorers and users of CSG started its commercial operations during 1996 at Bowen Basin of Queensland. CSG accounts for 27 per cent of Australian gas reserves. It is estimated that by 2030, 30% of the country’s domestic needs will be met by CSG with 50 per cent of gas demand in eastern Australia. All CSG reserves are in NSW and Queensland states.
With lots of questions raised from environmental and health perspectives, CSG has to stand its testimony by effectively addressing those concerns to emerge as a risk-free clean fuel for the future.