Geochemical Characteristics and Geological Significance of Coalbed Methane in Suzhou Mining Area of the Huaibei Coalfield

Qiang Wei; Song Chen; Herong Gui; Mingkun Zhao; Kongyu Zhao; Hubin Xia; Cancan Wu

doi:10.1021/acsomega.3c10512

Geochemical Characteristics and Geological Significance of Coalbed Methane in Suzhou Mining Area of the Huaibei Coalfield

ACS Omega. 2024 Apr 22;9(18):20086-20100. doi: 10.1021/acsomega.3c10512. eCollection 2024 May 7.

Authors

Qiang Wei^{1

2}, Song Chen^{1

2}, Herong Gui^{1

2}, Mingkun Zhao^{1

2}, Kongyu Zhao^{1

2}, Hubin Xia^{1

2}, Cancan Wu^{1

2}

Affiliations

¹ School of Resources and Civil Engineering, Suzhou University, Suzhou 234000, China.
² National Engineering Research Center of Coal Mine Water Hazard Controlling, Anhui 234000, China.

Abstract

In this study, gas contents, geochemical features, and origins of coalbed methane (CBM) and their influence factors were investigated on nos. 7 and 8 CBM reservoirs from the Suzhou mining area of the Huaibei coalfield. Results have shown that the selected CBM reservoirs are characterized by various thickness (0.50-9.19 m) and buried depth (619-1226 m), but have relatively better lithology of surrounding rocks. Coal samples have similar maturity (R_o,max = 0.71-1.05%), but show differences in chemical composition and macerals. Gas content of nos. 7 and 8 CBM reservoirs ranges from 6.13-12.25 m³/t, but the value of former is lower than that of later one overall. In addition, CH₄ is a predominantly component with a value of 88.23-99.00% (avg. 96.69%), and the heavy hydrocarbon gas (C₂₊) is 0.00-1.93% (avg. 0.41%). The δ¹³C_CH4 value ranges from -64.54 to -46.36‰ (avg. -53.92‰), and the δ¹³D_CH4 value is -224.36 to -211.75‰ (avg. -219.09‰). Based on the analysis of components and isotopic values, the CBM samples are thermogenic (20.92-71.30%; avg 50.09%) and secondary biogenic gases (28.70-74.49%; avg. 49.91%). Gas content shows changeable characteristics at a buried depth of 300-1300 m, which is affected by buried depth, reservoir temperature and pressure, M_ad and vitrinite. However, the CH₄ concentration shows no correlation with buried depth. Moreover, the buried depth is significantly positively correlated to δ¹³C_CH₄ and δ¹³D_CH₄. Based on the relationship between gas content and isotope values, it suggests that δ¹³C_CH₄ or δ¹³D_CH₄ may have a relationship with the main controlling factors of gas content.