Geological characteristics and development potential of deep coalbed methane resources in Shenmu-Jiaxian Block, Ordos Basin, China

China possesses abundant deep coalbed methane (CBM) resources with significant exploration and development potential, referring to depths greater than 2000 m. Deep CBM differs significantly from shallower formations in terms of accumulation and development patterns, necessitating detailed research for key blocks. The Shenmu-Jiaxian Block, situated in the northeastern part of the Ordos Basin, is currently in the early stages of deep CBM exploration, and its enrichment characteristics and development potential remain uncertain. In this study, we conducted a comprehensive analysis of the fundamental geological features of coal reservoirs in the study area using recent seismic data, well logs from over 300 wells, and analytical data from four core wells. We identified the main controlling factors and accumulation mechanism of CBM, and analogically assessed the development potential of deep CBM in the region. The targeting No. 8 deep coal, has the vitrinite reflectance of 0.7%~1.8%, indicating the coalification in the most parts of the study area is currently in the peak stage of thermogenic gas generation. The region exhibits considerable coal thickness, stable development, relatively simple tectonics, well hydrodynamic sealing, and favorable roof and floor sealing conditions, providing favorable conditions for widespread and continuous CBM accumulation. Among them, the southern area of Jiaxian demonstrates the most favorable CBM resource conditions. Compared to other deep blocks in the eastern Ordos Basin, the study area exhibits a notably higher proportion of free gas in coal seams. It is suggested that the adsorption gas in coals is mainly controlled by adsorption pressure, whereas the free gas is subject to dual controls of capillary pressure and buoyancy-gravity differentiation. These two trapping mechanisms jointly determine the vertical zonation and regional distribution of gas content in the deep coal seams. Taking the southern area of Jiaxian as an example, we summarized a typical enrichment pattern of deep CBM. Comparative analysis with the Linxing and Daning-Jixian Blocks indicates that the Shenmu-Jiaxian Block possesses a solid foundation of CBM resources, favorable reservoir alteration, and high production potential, hinting at promising prospects for large-scale development of deep CBM in this region. In addition, the Daning-Jixian block is characterized by high-rank coals, whereas the Shenmu-Jiaxia block consists of medium-rank coals. Therefore, this study contributes to the enrichment and refinement of the theory of deep coalbed methane accumulation, which holds significant instructive implications for the exploration and development of deep coalbed methane in China.