Discussion on Carbon Isotope Distribution Characteristics of Coalbed Methane and Gas Genetic Types

Using the measured results of coalbed methane (CBM) δ13C1 of more 170 groups, the paper has analyzed the distribution characteristics and statistical regularity of δ13C1 in coal seam gas in China. The values of δ13C1 are between -73.3‰ ∼ -27.3, increasing with the coal rank in general, and after anthracite, the value of δ13C1 goes to be stably fluctuating around -35‰. Based on the variation relationship between carbon isotope of CBM and coal rank, using the Rmax of coal vitrinite in coal as index, the origin of the coal seam gas is divided into three categories: secondary biogenetic gas, mixed genetic gas and thermogenetic gas. In addition, the paper has pointed out the gas genetic types of partial coal mining areas in our country.