Improving the CO2 well injectivity and enhanced coalbed methane production performance in coal seams

This paper reports on the performance comparison for different CO2-ECBM schemes in relatively thin unminable seams typical of Northern Appalachian coal basin using a horizontal well configuration. Numerical simulations based upon public-domain coalbed reservoir properties indicated that injection of pure CO2 is likely to result in only limited incremental methane recovery if any over primary recovery, due to the low injection rates that can be achieved. On the other hand, the presence of the nitrogen component in the injected gas stream is capable of improving the efficiency of enhanced methane recovery significantly without compromising the net CO2 injection rates, as a result of improved injectivity over pure CO2 injection. There is, however, a trade off between incremental methane recovery and produced gas purity due to early nitrogen breakthrough. (C) 2008 Elsevier B.V. All rights reserved.