Distribution characteristic of gas content of coal reservoir and its methane carbon isotope in the Xishan block

The gas-bearing properties is an important parameter to determine the exploration and development of coalbed methane(CBM). The methane carbon isotope(δ¹³C₁) can reflect the reservoir condition of CBM effectively. Based on the date of measured gas content from CBM well, the characteristic of gas content distribution in coalbed was analyzed, and the correlations and models of gas content, the burial depth of coalbed, geological structure were built. The characteristic of δ¹³C₁ distribution was discussed and it had an indicative function to the distribution of gas-bearing properties. Findings show that, the gas content in the Xishan block is an average of 6.87 m³/t, 8.4 m³/t, 9.6 m³/t in the No.2, 8 and 9 coalbed respectively. The gas content was mainly influenced by burial depth of coalbed and structural configuration. The δ¹³C₁ value of the No.8 in the study area ranges from -65.33‰ to -40.94‰ and its average is -45.88‰, and there was a positive correlation between coalbed gas content and δ¹³C₁. δ¹³C₁ generally is getting heavy with increase of gas content. δ¹³C₁ is mainly controlled by the coalbed methane desorption-diffusion-transport effect and hydrodynamic condition.