Identification of Favorable CBM Area Based on a Two-Tier of System

Coal bed methane is formed during the coalification stages and stored in coal seams, however the preservation of methane within the seams from the time of formation to present day predominantly depends on the evolution of local geological structure and the associated hydrogeological conditions following the coalification stage. Poor trapping conditions are more likely to result in an unfavorable CBM area. In this paper the evolution of geological structure and hydrogeological conditions of the North Shilou (NSL) CBM block is analyzed using an integrated approach. A two-tier system is developed to identify favorable CBM areas: Tier one considers geological structure and hydrogeological conditions; and Tier two the CBM reservoir properties. Two areas with different resource potential have been identified in the NSL block using this approach. One is characterized by higher gas content and saturation and limited groundwater recharge, where lithological trapping is predominant. The other, potentially less favorable, is characterized by lower gas content and saturation along with active groundwater recharge, where hydrodynamic trapping is predominant. The approach is able to explain reasonably the performance of the existing production wells in NSL block to date.