Geological significance of the conventional gas components, rare gas concentrations and their isotopic compositions in coalbed methane from the Luling coal mine in the Huaibei coalfield, China

Inert gases in CBM, such as helium (He) and argon (Ar), serve as important geochemical tracers that aid in studying the origin of CBM. In this study, 12 CBM samples were collected from the Luling coal mine in the Huaibei Coalfield. Gas composition analysis was conducted on these samples to measure the concentrations of methane, N2, CO2, He, and Ar. Additionally, the isotopic compositions of helium and argon in the gas samples were analyzed.Methane is the most prominent component in CBM, with concentrations ranging from 91.80% to 95.10%. Helium concentrations vary between 143.12 ppm and 580.23 ppm, falling short of the criteria for helium-rich gas. Argon concentrations lie between 62.73 ppm and 99.22 ppm. By examining the ratios of N2/Ar-a and He/Ar-r, the average contents of atmospheric nitrogen (N2-atm) and organic nitrogen (N2-org) were calculated to be 0.11% and 4.23%, respectively, concentrations typical of the shallow crustal region in this area. This study aims to quantify the relative contributions of crustal, mantle and atmospheric components to CBM in the Luling coal mine by integrating conventional gas compositions with He-Ar isotopes, and to evaluate how these noble-gas tracers record the tectono-thermal evolution and deep fluid migration associated with the Tan-Lu Fault Zone.