Coal Bed Methane (CBM)
What is coal bed methane?
A component of natural gas is a substance called methane (CH4). Coal bed methane
(CBM) is the same compound as the methane which is the primary energy source in
natural gas. Coal bed methane, however, is found in coal seams, and produced by
non-traditional means, and therefore while it is sold and used the same as
traditional natural gas, its production is very different. Coal bed methane is
generated either from a biological process as a result of microbial action or
from a thermal process as a result of increasing heat with the depth of the
coal. Often a coal seam is saturated with water and methane is held in the coal
by the pressure of the water.
Methane Molecule CH4
Characteristics of CBM
- The natural gas found in coal is "sweet" not "sour" as it does not contain
- it is generally methane with small amounts of carbon dioxide and nitrogen;
- it is generally of near-pipeline quality when produced and requires minimal
- it is generally produced at lower pressures than conventional natural gas.
How is the methane extracted from a coal seam?
Methane travels with the ground water being pumped from the coal from a well
drilled and completed in a coal seam that contains methane and fixed with a
water pump. Since methane has very low solubility in water it separates from the
water in the well before the water enters the pump. The extraction of CBM
involves pumping the available water from the coal seam aquifer in order to
reduce the water pressure that holds the gas in the coal seam. Water moving from
the coal seam to the well bore encourages gas migration toward the well. As this
water pressure is released, the gas will rise and separate from the water and be