Application of Isotope Geochemistry in Determining the Extraction Ratio of Target CBM from Multi-Seams

In most coal mines in China, the target coalbed methane (CBM) and its adjacent CBM generally require joint extraction before the target coalbed can be mined. But only the mixed CBM from multi-seams can be measured at the mouth of boreholes, and it is not possible to individually measure the CBM from a target coalbed. In view of this issue, the application of isotope geochemistry is proposed for the first time in the industry. Based on the law of mass conservation for the chemical composition of mixed CBM, according to the gas components and isotope difference characteristics of each coalbed in multi-seams, a calculation model for the extraction ratio from a target coalbed is established. Field experiments were selected in the Xiaotun Mine in Guizhou Province. The extraction ratio of the target coalbed 6m determined by isotope geochemistry ranged from 57.81% to 69.58%, and the deviation from the extraction ratio determined by the measured flow method was less than 7%. The residual gas content of the No. 14 mining face was calculated by combining the results of the above two methods, and the deviation from the measured residual gas content was less than 6%, indicating that the results obtained scientifically by isotope geochemistry were reliable. The results of the study can provide a new research tool for the judgment of target CBM extraction standards and, ultimately, ensure the safety of coal mine operation.