Relationship Between Microbial Communities and Hydrochemistry in Coalbed Water, and Their Controls on Biogenic Coalbed Methane Enrichment: Insights From the Dafosi Block, Southern Ordos Basin, China

ABSTRACT The generation of biogenic coalbed methane (BCBM) is closely associated with coalbed water and microorganisms. Thus, investigating the relationship between coalbed water microorganisms and hydrochemistry, along with their geological responses to BCBM enrichment, holds significant importance for identifying BCBM enrichment zones and the favourable areas for in situ coal microbial gasification. This study focuses on the Dafosi Block (southern Ordos Basin), where BCBM purity exceeds 99%. We analysed coalbed water geochemistry, microbial communities (bacteria and archaea), and their correlations with BCBM enrichment via environmental parameter determination, trace element testing, and 16S rRNA sequencing. Results show the coalbed water is neutral to weakly alkaline ClNa type with high total dissolved solids (TDS, average 13330.34 mg/L), characterized by a closed, low‐runoff environment free from fracturing fluid or surface water contamination. Bacteria exhibit higher diversity and abundance than archaea: all archaea are hydrogenotrophic methanogens (e.g., Methanobacterium , 58.56%), while bacteria (e.g., Pseudomonas and Acinetobacter ) supply methanogenic substrates via organic matter decomposition. TDS, Cl − , and Na + positively correlate with archaeal abundance but inhibit archaeal diversity; trace elements (Cs, Zn, Ga, Ti, Cr, As, Fe, and Ge) significantly affect microbial abundance. BCBM content negatively correlates with TDS but positively correlates with microbial abundance (bacteria exert a more notable effect). High TDS restricts microbial activity and abundance, reducing BCBM content, while low‐TDS areas (e.g., southern Dafosi Block) are more favourable for BCBM enrichment. These insights provide a theoretical basis for microbial‐geochemical synergistic regulation in coalbed methane exploration and in situ coal biological gasification.