It cannot be extracted from all bed types; coals, which are intermediate between brown coals and anthracite coals, are the best ones in terms of production. Kuzbass has abundant reserves of such coal, for instance.
The most common options are water or gel injection for fracturing, injection of air or air-air mixture through the well, and exposure of the reservoir to electric current.
Methane should be extracted from mines to prevent explosions. The United States was the first country that decided to turn it into a commercial enterprise. Ten per cent of gas is produced there using this technique. Production from coal beds is promising in Russia as well.
Gas inside the coal
Hydrocarbon gases are formed in coal beds during the coal matter metamorphism process, i.e. changing of its structure, properties, and composition under exposure to temperature and pressure. Their main component is methane, whose concentration in the mixture reaches from 80 to 98 per cent. Methane in coal beds can be free, occluded, or dissolved.
Methane: danger in mines
Methane is known for its ability to form explosive air mixtures. That’s why degassing, i.e. methane extraction is an integral part of field development in coal mines. This is the first production technique, which can be named “mining”. Volumes of produced methane are small in this case, and gas is used primarily for internal needs in the coal mining area.
Second production technique is commercial. Methane is in this case considered not as an associated gas but as a fossil mineral of its own. In case of commercial methane production, it is possible to supply the whole region with gas as an energy carrier and raw material. In addition, further coal mining operations become safer.
Gas recovery enhancement technologies are applied during a well construction stage to produce large volumes of methane.
First coal gas
The USA began were the first to extract methane from coal beds in the late 1980s, having identified the economic efficiency of such production. This industry is still most developed exactly there. In 2009, the methane production reached 56 billion cubic meters, which amounts to 10 per cent of the conventional gas production in the USA. It is also produced in Australia, Canada, and China.
Economic viability of commercial coal gas production in Russia driven by favorable geological conditions and gas content of coal basins. In 2003, Gazprom started estimating prospects of methane production in Kuzbass; first pilot wells were drilled then. So far, the pilot development of exploration wells with supply of gas to CNG filling stations was started. Stable level of methane extraction from coal beds in Kuzbass is planned in the amount of 4 billion cubic meters per year. In the long-term, this amount will grow to the range from 18 to 21 billion cubic meters per year to meet the gas demand in other south areas of Western Siberia.