Zhang Zhelin¹，Chen Biying^1,2，Liu Yi¹，Xu Zhanjie¹，Finlay M. Stuart³，Xu Sheng¹

(¹ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China; ²School of GeoSciences, University of Edinburgh, Grant Institute, Edinburgh, EH9 3FE, UK; ³Scottish Universities Environmental Research Centre (SUERC), East Kilbride G75 0QF, UK)

Abstract: Coalbed methane (CBM) is a significant unconventional natural gas resource; its generation, migration, accumulation, and production are governed by the interactions among multiple spheres within sedimentary basins. Understanding the evolutionary history of coal-bearing strata fluids is crucial for scientifically assessing resource potential and optimizing development strategies. This study collected CBM samples from five gas-producing blocks across the northern (Gujiao, Yangquan), central (Yushe), and southern (Shizhuang, Panzhuang) regions of the Qinshui Basin. By analyzing the concentrations and isotopic compositions of noble gases (He, Ne, and Ar)—and integrating open-system Rayleigh fractionation models with production performance data—the study elucidates the mixing, migration, and loss of coal-bearing strata fluids driven by multi-sphere interactions, as well as the implications of these processes for resource development.

The results show that the CBM samples have ³He/⁴He ratios of 0.015–0.028 R_A, indicating a predominantly crustal radiogenic origin of helium. The ⁴⁰Ar/³⁶Ar-³⁶Ar relationships further reveal mixing between atmospheric-derived and crustal fluids. Calculated cumulative ⁴He ages range from 1 to 23 Ma, significantly younger than the Carboniferous–Permian depositional age, indicating widespread Cenozoic fluid loss associated with tectonic uplift. Preservation conditions vary substantially among blocks and are jointly controlled by burial depth and coal rank. The ⁴He/⁴⁰Ar* ratios distinguish northern and southern CBM systems, reflecting differences in gas and noble-gas retention associated with coal rank and adsorption capacity. Notably, ⁴⁰Ar* accumulation ages show a strong positive correlation (R² = 0.89) with the proportion of desorbed methane, suggesting that argon preservation age can serve as an indirect indicator of adsorbed methane preservation. These results demonstrate the potential of noble gas isotopes for tracing coal-measure fluid evolution and evaluating CBM preservation and development potential.

Keywords: Noble gases; Coalbed methane; Gas accumulation; Gas production; Qinshui Basin

Author Profile (first author):

Zhelin Zhang Female, PhD Candidate, mainly engaged in gas geochemistry research. E-mail: zzl_8@tju.edu.cn