How is it Produced?

Coal Bed Methane is produced by drilling a well which contacts the coal seams. Once water is pumped out, the pressure is lowered and gas migrates through the coal, up the well bore to surface.

Most coals contain methane, but it cannot be economically produced without open fractures present to provide the pathways for the desorbed gas to migrate to the well. As long as the pressure exerted by the water table is greater than that of the coal the methane remains trapped in the coal bed matrix. Coal cleats and fractures are usually saturated with water, and therefore the hydrostatic pressure in the coal seam must be lowered before the gas will migrate.

Lowering the hydrostatic pressure in the coal seam accelerates the desorption process. CBM wells initially produce water primarily; gas production eventually increases, and as it does water production declines. Some wells do not produce any water and begin producing gas immediately, depending on the nature of the fracture system. Once the gas is released, it is usually free of any impurities; is of sufficient quality, and can be easily prepared for pipeline delivery.

Coals in the UK are potentially analogous to those formed in Eastern areas of the US. Many of these Eastern US coals do not require significant amounts of water to be removed to initiate methane production. These coals are often exploited by way of horizontal drain-holes from a single bore-hole. Each individual well may have up to 3,500-feet of lateral extent within a single coal seam. Several laterals can be drilled from a single wellbore to exploit several seams or to take advantage of several cleat (fracture) trends. Each leg would not necessarily be horizontal but would closely follow the dip of the individual seam. Many of the coal seams are often less than five-feet thick, requiring the drilling contractor to exercise great care in steering the drill bit.