Abstract:

The value of δ¹³C₁ of coal bed gas in Shanxi and Taiyuan Formations in Qinshui Basin is between-2.963%～-3.539%,which is clearly lower than the δ¹³C₁ value(-2.701%) of simulation test and that calculated by empirical formula.The gas is thus considered to be secondary coal bed gas.The contents of methane in coal bed gas in the study area is more than 98%,and there is no exchange of methane and CO₂ isotope,the preservation condition is good.So it is suggested that desorption diffusion migration shuld be the real origin of the secondary coal bed gas in the study area.

Key words: coal bed gas, origin, δ¹³C₁, secondary action, Jingcheng area