How is coal bed methane (CBM) different?
Coal bed methane (CBM), also known as coal seam gas (CSG), is found naturally in underground coal seams. It poses a serious risk to humans in underground coal mining, which is why canaries were once used to detect it. CBM is usually extracted by 'de-watering' coal seams, in other words by pumping all the water out of the coal seams so that the gas follows under negative pressure. Fracking (or hydraulic fracturing) can also be used as a technique to win CBM by making it easier for the gas and water to flow through the coal.
Stages of CBM extraction
A project to extract CBM onshore has several stages:
- Exploration – Promoters gather and assess data to determine the availability of CBM. This work includes seismic testing, core sampling and horizontal exploratory drilling. It can also include fracking.
- Moving into production – Well sites are prepared for full-scale extraction, and more vertical and horizontal boreholes are drilled. Materials including drilling (and fracking) fluids are brought on site. A facility is built to treat the waste water produced. A gas treatment facility may also be needed to make the gas suitable for adding to the supply system.
- Production – The wells are de-watered (and/or fracked) to extract CBM, which may need to be purified before combustion or export to the gas network. Waste water is treated before discharge. Sludge from the water treatment facility is taken off site for disposal elsewhere.
- Decommissioning and restoration – All sites are restored to their original condition.
In the UK, two CBM proposals have gone beyond the exploration phase, and planning permission has been sought for commercial production, and in one case been granted. Both of these proposals are in Scotland.