Coal bed methane
What is Coal Bed Methane? Coal-bed methane (CBM) is a form of natural gas that is trapped in the carbon structure of coal seams. That is, the methane is absorbed to the surface of the coal. It is an unconventional resource, as the methane contained in the coal does not migrate to other rock strata.
Its extraction involves drilling down vertically and then horizontally in the coal seam.
The gas is released in a controlled and safe manner by pumping out the water that occurs naturally in coal seams, or ;cleats', to reduce the underground pressure on the coal.
This is the basic principle of CBM extraction: wells are drilled into the coal seams, and the water is removed to reduce the pressure on the coal so the gas can be collected. If dewatering stops, the coal seam and the well fill with water, which automatically prevents the gas from being released.
The entire process is reversible and any gas left in the wellbore is re-adsorbed by the coal, which makes CBM inherently safer than conventional gas reservoirs. The decline in conventional gas production in the North Sea and an increased understanding of exploitation techniques have resulted in greater interest in CBM in the UK. Natural gas from coal has the potential to be an important new source of energy for this country.