Coal Bed Methane Enhancement Techniques: A Review

Paper investigates the potential impact of Coalbed methane (CBM) in near present and future. CBM is a natural gas that mainly consists of methane present in physically adsorbed state on the surface of porous coal seam under geothermal pressure. CBM is a cleaner fuel which can be used in the transportation industry, conventional power generation, and many other ways. 50-60% of CBM recovery can be obtained under primary operations and enhancement techniques can increase recovery as high as 80%. Recovery enhancement can be made through temperature increase, pressure release or by selective adsorption in which an injection gas displace methane from coal surface. Recovery through the use of CO2, N-2, CO2 & N-2 mixture is discussed in detail. Underground coal gasification can be used to recover energy from methane depleted, unminable coal reservoirs and has many advantages over surface mining. CBM consists of both thermogenic and biogenic origin. Depleted CBM reservoirs are observed to produce methane even after recovery is done. Native naturally occurring microbes decomposes coal into methane which explains biogenic origin, through a series of reaction. Kinetics of these decomposition reaction could be escalated significantly through the injection of nutrients and genetically enhanced methanogens. These processes has a great potential and could provide a fossil fuel which is almost renewable as large amount of methane can be generated from small amount of coal.