Abstract
Uncertainties of CO2 injection-sequestration in a CBM is driven by the complex process of gas desorption-controlled mechanism attributed to the natural characteristics of CBM and to the impact of the wells engaged in the reservoir. This work presents the reservoir characterization and simulation process 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 Upper Freeport) are the subject of this pilot CO2 sequestration project. Methane is produced from both coal seams; however CO2 is injected only in the Upper Freeport which includes four wells. The shallower 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 exhibit different production and injection behavior.
A commercial simulator is used for modeling. Three realizations of the reservoir were built and history matched base on different Langmuir isotherms. The model which leads to a better approximation of the actual injection profile is selected for further analysis. Upper Freeport formation characteristics, its CO2 storage capacity and CO2 distribution in the reservoir are presented in this article. The model can be used to define safety margins for the maximum bottom-hole pressure during injection.
