Geological characteristics of low rank coalbed methane, China

Low rank coalbed methane is a very important and potential field of coalbed methane exploration and exploitation in China. The geological structure backgrounds of coal-bearing basins are complicated, and many coalbeds are reconstructed by multiperiod and multiproperty structures and combinations, as well as stress-strain. The accumulation and enrichment of coalbed methane have the following characteristics: big thickness, multiple beds, low gas content, preferable permeability, great resource, and abundance. The thick and widely distributed coalbeds and huge coal resources offset the shortcoming of low gas content, probably leading to the good prospect of exploration and exploitation. Matrix shrinkage effect induced by desorption causes high permeability in exploitation of low rank coalbed methane reservoirs, which is good for coalbed methane exploitation, and prone to form industrial gas flow. Low rank coalbed methane reservoirs have a simple forming process, including one deposition and one adjustment. If the main controlling factors, such as structure, coal-forming environment, and hydrologic geology, are matched well, the enriched coalbed methane zone with high production would be formed. Key words: coalbed methane, low coal rank, permeability, hydrological condition, reservoir formation