Coalbed Methane (CBM)
Definition - What does Coalbed Methane (CBM) mean?
Coalbed methane (CBM) is an unconventional form of natural gas with 95 percent of its volume comprising of methane (CH4), a naturally occurring gas. It's trapped in the carbon structure of coal deposits or coal seams when the methane is absorbed on the coal surface. CBM is formed during the coalification process where organic material such as trees and plants turn into coal when they are suddenly buried and heated.
It's called an unconventional resource because the methane in the coal does not migrate to other strata of rock surrounding it. CBM is a stable and valuable source of energy when extracted efficiently.
Trenchlesspedia explains Coalbed Methane (CBM)
The extraction of CBM involves drilling vertically and then horizontally into the coal seam. The water is pumped out from the coal seam lowering the reservoir pressure and allowing the methane held by the water pressure to follow the water to the surface where it is captured and stored via pipelines in storage facilities. Reservoirs containing CBM have layers, and contain cleats (orthogonal fracture sets) perpendicular to the bedding. Since coal seams have low permeability, stimulation by hydraulic fracture or cavity completion is necessary to produce it efficiently.
CBM wells unlike conventional gas wells produce large amounts of water compared to gas initially, but overtime, the volume of water decreases and the gas rate increases.