Carboniferous-Permian coal-bearing depositional system and its controlling role of coalbed methane in Hancheng area in Ordos Basin

The geological conditions for coalbed methane are complicated in Hancheng area of the Ordos Basin. The characteristics of coal-bearing depositional system work as the main controlling factor for the enrichment of coalbed methane. According to the features of coal-bearing sediments in Carboniferous and Permian in Hancheng area, the Taiyuan Formation constitutes of lagoon-tidal-barrier island sedimentation and carbonate flat sedimentation while the Shanxi Formation constitutes of fluvial-dominated delta sedimentation. The changes of sedimentation, the thickness of coalbed, the petrophysical property and the lithology of roof and floor of coalbed are directly concerned to analyze the influence of sedimentary environment on CBM enrichment. The coalbed no.3 is thin and even pinches out locally. The coalbed no.5, which is thick and stable, is widespread in the study area. The roof and floor of coalbed are mainly mudstone, sandstone and siltstone. The coalbed with stable structure and thick mudstone as roof and floor is favorable for the enrichment and accumulation of coalbed methane. The area to the east of Baimatan town is the exploration target for 2 sets of coalbed.