Field-scale complexities associated with production of CH4 from coal bed methane reservoir

Coal Bed Methane (CBM) is a kind of natural gas found in coal seams as adsorbed gases, unlike free gases in a conventional reservoir. These coal beds are complex, with a wide distribution of porosity from nano to micro and permeability in order of change. This review study examines complexities associated with understanding CBM reservoirs and important processes that must be considered during production. CBM extraction requires methane desorption from the coal surface, which is achieved by lowering the CBM reservoir pressure by dewatering the associated groundwater. The reservoir pressure reduction due to dewatering and subsequent production of CBM gas results in significant modification of the reservoir properties, particularly porosity and permeability. Thus, it has been recommended from the present study that an improved understanding of the storage and transmission of gas from a coal-seam requires a coupled effect of geo-mechanical stresses and desorption effect for a spatially and temporally varying pore network coal-seam geometry. Given the complexities and associated challenges in modelling these effects at the field scale, we present a set of practical queries for further investigation. This discussion addresses the need to study the environmental impacts associated with producing natural gas from a CBM reservoir.