Investigating coalbed gas productivity response from hydrogeochemical and microbial perspectives: A case study of the Liulin block, eastern Ordos Basin, China

Abstract

The benefits of coalbed gas (CBG) development are directly affected by the production capacity level. Previous studies of CBG productivity response have mainly focused on the hydrogeochemical characteristics of produced water, and paid less attention to the correlation between microbial communities and productivity. This study focuses on nine CBG wells in the Liulin Block of the eastern Ordos Basin, systematically analyzing the CBG genesis, as well as the relationships between hydrogeochemical parameters, microbial community characteristics and CBG productivity. The results show that the CBG in Liulin Block is a mixture of secondary biogenic gas and thermogenic gas, and the proportion of biogenic methane is 48.0 % to 49.7 %. 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. 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. 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.