Coal Bed Methane (CBM)
Coal bed methane is methane that is or can be recovered from coal seams. Also known as Coal Seam Gas. CBM is recovered by drilling wells into suitable coal seams and then reducing pressure in the rock, usually by pumping out water, which may be saline and present environmental issues, until the methane can be desorbed from the coal. CBM, unlike conventional natural gas, is not trapped beneath a Seal but is adsorbed into the coal. It can therefore occur in coal deposits which are laterally very extensive. Production rates are typically much less than for conventional gas. Depletion rates are typically quite slow and wells may produce for many years. CBM may also be produced as a safety measure before coal is mined to reduce the incidence of potentially explosive gas mixtures during mining operations. See Coal Mine Methane.