Geological features and exploration practices of deep coalbed methane in China

China boasts abundant deep coalbed methane (CBM) resources. Positive progress in the exploration in recent years has established CBM as a strategic replacement for current unconventional natural gas in the future. However, the commercial exploitation of deep CBM faces challenges of complex geological and engineering conditions. In this study,we investigate the geology of deep CBM in typical regions across China and review advances in relevant theoretical and technical study, proposing the prospects for the exploration and production of deep CBM. The results indicate that deep CBM reservoirs exhibit the geological and engineering characteristics of strong heterogeneity, enrichment in both free and adsorbed gas, and high plasticity compared to their shallow counterparts. Deep medium- to low-rank coal reservoirs provide substantial storage space dominated by primary plant tissue pores. In contrast, deep medium- to high-rank coal reservoirs contain micropores and fissures, with the former dominated by organic pores and the latter consisting primarily of cleats and exogenetic fractures. Over years of addressing technological challenges, SINOPEC has preliminarily developed a series of technologies for the selection and assessment of deep CBM target areas, sweet spot prediction,horizontal well drilling, and hydraulic fracturing with fractures effectively propped, which serve to provide effective support for breakthroughs achieved in deep CBM exploration. It is recommended to focus on the accumulation patterns,sweet spot identification, production technologies and policies, and production rules of deep CBM in future study. Additionally, it is advisable to develop efficient drilling and completion technologies for horizontal wells in thin coal seams, along with technologies for fracturing with reduced cost and enhanced efficiency for reservoir stimulation.