Enhanced Coalbed Methane Recovery

Abstract At present, coalbed methane is being recovered by means of reservoir pressure depletion. While this method is simple and effective, it is not efficient. Reduction in reservoir pressure deprives the fluids of the energy necessary to flow to the wellbore. Furthermore, there is a practical and economic limit on the extent to which reservoir pressure can be reduced. It is estimated that reservoir pressure depletion strategy of coalbed methane production will permit the recovery of 50% or less of the gas-in-place. This paper discusses an alternate method of coalbed methane recovery which consists of nitrogen flooding a coal seam. Lab research has shown that essentially all methane sorbed on coal can be stripped by nitrogen without necessarily reducing the total system pressure. That is, methane desorption from coal is achieved by reducing the partial pressure of methane rather than merely the total pressure. Lab and modeling results are presented to demonstrate how nitrogen injection in coal can accelerate methane production rates and enhance reserves. Scoping process economics of enhanced coalbed methane production also appear to be attractive.