Research on the geochemical characteristics of coalbed methane and relationship between gas-logging and measured gas component in Guxu mine of southern Sichuan coalfield, China

Coalbed methane (CBM) is an environmentally friendly and clean energy. The research on its genetic types and gas content calculation methods plays an essential role in predicting CBM resources. In this paper, the plane and vertical responses of the measured gas composition data of CBM and gas-logging data are analyzed by sampling eight coals from six layers of the Late Permian Longtan Formation in the Guxu mining area of the southern Sichuan coalfield and measuring the gas content, gas composition, stable isotopic composition, and gas-logging data. The results show that all the coal seams in the study area meet the requirements of CBM exploitation, and the gas content in C 14 and C 17 layers is relatively high, reaching 19.72 m 3 /t and 20.27 m 3 /t, respectively. Methane is the main gas component of each coal seam, and the volume ratio of methane gas ranges from 88.03 to 98.51%, with an average of 93.27%, which is a typical dry gas characteristic. The CBM in this area is a thermogenic gas reflecting by δ 13 C(CH 4 )- δ D(CH 4 ) and δ 13 C(CH 4 )-δ 13 C(CO 2 ) diagrams. In the plane, there is a significant correlation between the measured gas components (methane and total hydrocarbon) in the laboratory and gas-logging data in nature ( R 2 >0.95), meeting the dHyperbl function model. In the vertical direction, there is an apparent correlation between the gas-logging data of CBM and the buried depth of coal seam, indicating that the measurement results of CBM are greatly affected by the buried depth. However, the correlation between the measured gas component and the buried depth is not good, indicating that the measured gas component is restricted by many factors (such as coal thickness, coal quality, and maturity). The results provide a theoretical basis for CBM content calculation and resource prediction in a similar area.