Microbial-mediated Changes during the Brine–Shale–Microorganism Interaction Process

Abstract Exogenous microorganisms are introduced into the shale gas reservoir during hydraulic fracturing, but the microbial-mediated changes in the process are yet unclear. Here, a brine–shale–microorganism interaction was simulated in the laboratory for 150 days. Biogenic methane was generated rapidly in 0–16 days, then slowly in 16–40 days and stopped after 40 days, accompanying by brine alkalization. Formation trend of biogenic methane may be independent of the substrate type under the same conditions. Biofilms accelerated mineral dissolution and facilitated secondary mineral formation. Microbial action enhanced the complexity and heterogeneity of macropore structure. Archaeal community structure changed little, while bacterial community structure altered significantly, with bacterial diversity decreasing. Predominant Proteobacteria in the early stage almost disappeared, while Firmicutes, Bacteroides and Desulfobacterota gradually increased. Firmicutes showed a transfer tendency from brine to biofilms. Proteiniphilum and Petrimonas were mainly distributed in brine, whereas Sedimentibacter and Clostridium_sensu_stricto_13 dominated in biofilms. Desulfovibrio was highly distributed in both brine and biofilms. Loss of microbial diversity and the self-assembly of symbiotic microorganisms with cooperation and competition occurred in response to the changes in the shale environment, which also affected methane production, brine pH, and both mineral composition and pore structure.