The injection of carbon dioxide (CO2) in deep, unmineablecoalbeds can enhance the recovery of coalbed methane (CBM) and at the same timeit is a very attractive option for geologic CO2 storage asCO2 is strongly adsorbed onto the coal.
Existing CBM numerical simulators which are developed for the primary CBMrecovery process, have many important features such as: (1) a dual porositysystem; (2) Darcy flow in the natural fracture system; (3) pure gas diffusionand adsorption in the primary porosity system; and (4) coal shrinkage due togas desorption; taken into consideration. However, process mechanisms becomemore complex with CO2 injection. Additional features such as: (1)coal swelling due to CO2 adsorption on coal; (2) mixed gasadsorption; (3) mixed gas diffusion; and (4) non-isothermal effect for gasinjection; have to be considered.
This paper describes the first part of a comparison study between numericalsimulators for enhanced coalbed methane (ECBM) recovery with pureCO2 injection. The problems selected for comparison are intended toexercise many of the features of CBM simulators that are of practical andtheoretical interest and to identify areas of improvement for modeling of theECBM process. The first problem set deals with a single well test withCO2 injection and the second problem set deals with ECBM recoveryprocess with CO2 injection in an inverted five-spot pattern.