Methane production via anaerobic digestion in coal reservoirs with the participation of supercritical carbon dioxide

Supercritical carbon dioxide (Sc-CO2) extraction and Coalbed Gas Bioengineering (CGB) offer synergistic potential for CO2 utilization and coalbed methane enhancement, yet the coupled biogeochemical mechanisms remain elusive. This study investigates the dual role of Sc-CO2 in promoting biomethane production using high-pressure anaerobic digestion simulations (8.60 MPa, 35 °C) with indigenous microbial consortia. The system's physicochemical and biological evolution was systematically characterized through the integration of time-series gas monitoring with XPS, GC-MS metabolite profiling, and 16S rRNA sequencing. Results demonstrate that Sc-CO2 functioned as a “chemical mobilizer,” selectively extracting recalcitrant surface oxygenated groups (COO−, C=O) and releasing bioavailable alkanes and alcohols to alleviate substrate limitatiHns. Despite initial stress-induced inhibition, the microbial community, dominated by resilient Firmicutes, successfully adapted via membrane regulation. Crucially, quantitative carbon mass balance analysis reveals a coupled metabolic network where hydrogenotrophic methanogenesis utilizing injected CO2 accounted for 83% of the total methane carbon, while acetoclastic pathways driven by coal-derived organics contributed 17%. Ultimately, the system achieved a biomethane yield of 0.785 mmol/g-TOC and a CO2 bioconversion efficiency of 6.98%. These findings validate the feasibility of transforming coal reservoirs into “subsurface bioenergy reactors,” providing a rigorous mechanistic framework for simultaneous geological carbon sequestration and renewable energy recovery.