Analysis of major controlling geological factors on coalbed methane enrichment and accumulation model of low coal rank in Tuha-Santanghu Basin

Abstract The low-rank coalbed methane resources in the Tuha-Santanghu Basin are rich, but the degree of exploration is low. The main controlling factors and accumulation model of coalbed methane accumulation are insufficiently understood, which restricts the exploration and development practice. In order to find out the main controlling factors and accumulation mode of low rank coalbed methane in Tuha-Santanghu Basin, from the aspects of low coal rank coal seam distribution, coalbed methane gas types and origins, comprehensive considerations such as hydrogeology, tectonic and sedimentary conditions, etc, the reservoir-forming conditions of low rank coalbed methane gas are analyzed, and the accumulation model is proposed to further explore direction. The results show that hydrogeological condition affect the generation and enrichment of low rank coalbed methane in this area, which is an important conditions for the formation of low rank coalbed methane. It is advantageous to save the low-rank coalbed methane with weak runoff. Different tectonic conditions have different effects on the preservation of coalbed methane, which can be divided into favorable preservation and destructive preservation. The influence of coal-forming environment on coal’s gas-generating potential, top and bottom lithology and coal reservoir physical has an important impact on low rank coalbed methane. The comprehensive study proposes two types of low-rank coalbed methane accumulation models in the Tuha-Santanghu Basin: gas accumulation model of basin margin slope zone and gas accumulation model of stagnant confined water + lithologic plugging coalbed methane in small fault sag. Comprehensive analysis shows that coal-bearing slope zone of basin margin with favorable hydrogeological conditions and coalbed methane reservoir with good preservation conditions in small fault sag with retaining confined water+lithologic plugging characteristics will be the key exploration area in the future.