Enhanced coal bed methane production and sequestration of carbon dioxide in unmineable coal seams

The process of modeling reservoirs that are controlled by desorption such as Coal Bed Methane has always been challenging due to the complexities associated with flow of fluids in these types of reservoirs. These complexities become more notable while the injection process is taking place since interaction between the injected gas alters the coal properties with respect to time.;This manuscript summarizes the results of a study that includes reservoir simulation and modeling efforts that are focused on natural gas production and subsequent CO2 injection into an unmineable coal seam in the Marshall Country West Virginia. Two coal seams (Pittsburgh and the Upper Freeport) are the subject of this pilot CO2 sequestration project. Methane is being produced from both coal seams, however CO2 is injected only in the Upper Freeport formation (the deeper of the two formations) which includes four wells, two of them being shut-in. The Pittsburgh coal is used to observe and detect any possible leakage.;The objective is to build a reservoir simulation model that is capable of matching the methane production history and forecast field potential capacity for CO2 injection and sequestration. Although injection has taken place in two reasonably close wells, these wells perform differently as far as the production history and injection behavior is concerned.;A commercial numerical reservoir simulator CMG (Computer Modeling Group) is used for modeling this reservoir. Three different realizations of the reservoir were built base on different Langmuir isotherms. This step is succeeded by history matching process. The model which leads to a better approximation of the actual injection profile is selected for further analysis.;The outcome of this work includes the reservoir parameters of Upper Freeport formation. The coal seam capacity to sequester CO2 along with the injected CO2 path is forecasted. The lessons learned from this study will be used to define the safety margins as far as the maximum bottom-hole pressure is concerned.