The primary energy source of natural gas is a substance called methane (CH4). Coal bed methane (CBM) is simply methane found in coal seams. It is produced by non-traditional means, and therefore, while it is sold and used the same as traditional natural gas, its production is very different. CBM 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 depth of the coal.

CSG is methane gas that is trapped in coal deposits; it is a natural gas formed as a by-product during the coalification process whereby organic matter is turned into coal. To extract the gas a hole is drilled down into the coal seam and is cased. The coal seam is perforated which then enables the gas to flow to the surface, where it is gathered and processed as required. Unlike conventional natural gas reservoirs, where gas is trapped in the pores or void spaces of a rock such as sandstone or limestone, methane trapped in coal is adsorbed onto the coal surface (cleats and joints) or micropores and held in place by reservoir and (water) pressure. Hence the coal is the source and the reservoir for the methane. To extract the CSG wells are drilled into the coal seams – the water is pumped out and the CSG is then released (desorbed) from the coal. If the pressure within the seam is high enough the gas may flow to the surface unaided, if not the gas must be pumped. Various techniques have been developed to enhance the rate of desorbtion, including the pumping of carbon dioxide underground to increase field pressure (which leads some CSG promoters to describe it as a form of “clean coal”). Like shale gas, seam gas is often called unconventional gas. In the past though this gas was viewed as more of a hazard to miners than a benefit. The micropore surface area of coal is very large, and can potentially hold significantly more methane per unit volume than most conventional reservoirs. The amount of gas trapped in the coal is a function of coal rank, pressure and temperature. Coal generally has lower permeabilities than conventional reservoirs so the rates of production are usually lower. In order to achieve optimal production rates, one method used is to stimulate the coal reservoirs by hydraulic fracturing. Newer drilling techniques like surface to in-seam (SIS) make fracturing unnecessary and also increase productivity. CSG is naturally an odorless gas that is used just like any other form of conventional gas