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Coal bed methane

Coal bed methane (CBM) is another form of unconventional gas, formed by the decomposition of organic material found in coal that is too deep or too poor quality for commercial mining.

Although occasionally found at shallow depths, CBM is often buried 1,000 to 2,000 meters underground. It is most often produced using vertical wells, although horizontal drilling is becoming increasingly common in some areas.

To extract the gas, water is pumped out of the coal seam to reduce the pressure that holds gas in the seam. CBM is not very soluble in water and easily separates from the coal seam as pressure decreases, allowing it to be piped out of the well separately from the water. The water removed during the depressurization process is then re-injected into the subsurface.