Matrix shrinkage and swelling effects on economics of enhanced coalbed methane production and CO ₂ sequestration in coal

Proven coalbed methane reserves have been pegged at 18.5 tcf, representing 10% of the total natural gas reserves in the US. The Palmer-Mansoori model for coal shrinkage and permeability increases during primary methane production was re-written to account for coal swelling caused by CO ₂ sorption. The generalized model was added to PSU-COALCOMP, a dual porosity reservoir simulator for primary and enhanced coalbed methane production. Injectivity of CO ₂ decreased when swelling occurred. Profits from a project might be affected positively or negatively by swelling and shrinkage effects. The effects of swelling and shrinkage were not limited to the injection wells; production wells could see a permeability increase or decrease. Accurate values of Young's modulus and Poisson's ratio are necessary to make reliable predictions. Net present value analyses of the simulation results included profits due to methane production, and potential incentives for CO ₂ sequestered. This is an abstract of a paper presented at the SPE Eastern Regional Meeting (Morgantown, WV 9/14-16/2005).