Study on characteristics comparison of low rank coal coalbedmethane reservoirs at home and abroad

China’s low rank coalbed methane resources are abundant, but the degree of exploration and understanding is low, and the research on coalbed methane accumulation conditions, coal reservoir characteristics and resource potential is insufficient.Based on CBM geological data from the Erlian Basin, Hailar Basin, Zhundong Area, Tuha Basin, Powder River Basin in the United States and the Surat Basin in Australia, this paper first analyzed the distribution characteristics of low rank coal and the origin of CBM in China. It then discussed the characteristics of the geological structure of evolution and analyzed the characteristics of coal rank, composition of coal, gas content, porosity, permeability and hydro-geological conditions. The differences of CBM content, reservoir property and hydro-geological conditions in the low coal rank basins were pointed out, and the reasons for the differences in the gas content between domestic and foreign basins were expounded. The results show that the geological and structural characteristics of the low coal rank basins in China are similar to those in foreign countries, and CBM is mainly secondary biogenic gas.The gas content both at home and abroad increases first and then decreases as the burial depth increases. The gas content of the low coal rank basins in China and the Powder River Basin is between 0～4 m3/t,but the gas content of in the low coal rank basins is lower than that in the Powder River Basin and the Surat basin in Australia under the same buried depth. The hydro-geological condition of low coal rank CBM gas content difference is one of the most important factors, and the poor hydro-geological conditions in China causes the low coal bed gas content. But the hydro-geological conditions of the Powder River Basin and the Surat Basinare good, so the gas content is high.The permeability of basins varies greatly from country to country. The permeability of domestic basins is poor, generally less than 1.0×10-3 μm2. The permeability of the Powder River Basin and the Surat Basin is good, and the permeability is 1～2 orders of magnitude higher than that of domestic low coal rank basins. Therefore, there is a great difference in low rank coalbed methane resources between the domestic basin and the Powder River Basin in the United States and the Surat basin in Australia.