132 / 2025-04-03 21:02:11

Investigating Coalbed Gas Productivity Response from Hydrogeochemical and Microbial Perspectives: A Case Study of the Liulin Block, Eastern Ordos Basin, China

Coalbed gas; Productivity response; Hydrogeochemistry; Microbial community; Ordos Basin; Liulin Block

Theme 4: Microbial and Biogeochemical Evolution through Time > Session 4a: Control of Microbial and Biogeochemical Cycling on Hydrocarbon Formation and Critical Metal Mineralization

Coalbed gas (CBG) is a crucial resource for the global energy structure adjustment and green low-carbon transformation, and its development benefits are directly affected by the production capacity level (Zhu et al., 2024). Studying the response mechanisms of CBG productivity not only deepens the understanding of the CBG production process, but also holds significant importance for optimizing development technologies and improving extraction efficiency of CBG. Previous studies of CBG productivity response have mainly focused on the hydrogeochemical characteristics of produced water (Owen et al., 2015), and paid less attention to the correlation between microbial communities and productivity. The microbial communities play a key role in the formation and evolution of CBG by decomposing organic matter in coal seams or degrading and modifying thermogenic components (Fu et al., 2024). Therefore, microbial communities in coalbed water may have potential response relationship with CBG productivity, but systematic study and in-depth discussion are still lacking. In this study, nine CBG wells in the Liulin Block of the eastern Ordos Basin were taken as the research objects, and the CBG genesis, hydrogeochemical characteristics and microbial community characteristics were systematically analyzed. Combined with the production data of the CBG wells, the response relationship between hydrogeochemical parameters, microbial community characteristics and CBG productivity was deeply studied. The results show that the CBG in Liulin Block is a mixture of secondary biogenic gas and thermogenic gas, in which the formation pathway of secondary biogenic gas is CO₂ reduction, and the proportion of biogenic methane is 48.05% to 49.66%. In the water samples, the contents of Na⁺, HCO₃^- and Cl^- are relatively high, and the contents of Ca²⁺, Mg²⁺ and SO₄^2- are low. The total dissolved solids (TDS) content is positively correlated with the average daily production of CBG, and the concentration of HCO₃^- is negatively correlated with the average daily gas production. The concentration of elemental Sn in the produced water is significantly correlated with average daily gas production (correlation coefficient of 0.68, p ≤ 0.05). Positive δ¹³C_DIC values indicate the occurrence of microbial methanogenesis. Analysis of the microbial community shows that the bacterial community exhibits significant functional diversity, with Hydrogenophaga having the highest relative abundance and a positive correlation with average daily production of CBG. The archaeal community is dominated by methanogenic archaea, and the average percentage of Methanobacteriaceae is as high as 94.1%. From the perspective of community diversity, the Operational Taxonomic Units (OTU) number, Chao1 and Ace indexes of the archaeal community show a positive correlation with average daily gas production. This study provides a novel perspective for research on microbial indicators of CBG production. The findings offer significant implications for advancing the understanding of CBG generation processes and formulating optimized development strategies.