Microbial consortia controlling biogenic gas formation in the Qaidam Basin of western China

Abstract

Knowledge of what controls the activity of subsurface microbial communities is critical for assessing and managing biogenic methane resources. In this study, 19 formation waters and five gas samples were collected at depths of 800 to 1900 m from Quaternary biogenic gas fields of the Qaidam Basin, China. The formation waters were brines with chloride (Cl) concentrations from 1200 to 2700 mM. Bacterial 16S rRNA gene copies ranged from 3.75 × 104 to 2.23 × 106 copies mL−1 of water, and those of archaea ranged from 2.44 × 103 to 4.66 × 107 copies mL−1 of water. Both bacterial and archaea 16 s rRNA gene copies were negatively correlated with Cl concentration. The microbial community structure differed significantly depending on Cl concentrations. At high Cl waters (>1800 mM), the microbial community showed a halophilic signature made up of several abundant taxonomic groups within Firmicules, γ‐Proteobacteria, and methylotrophic Methanosarcinales. At low Cl, Firmicules and hydrogenotrophic methanogens were dominant members. The proportion of inferred hydrogenotrophic methanogens decreased from 89% to 14% of total archaeal reads with increasing Cl concentration; in contrast, methylotrophic species increased from 11% to 85%. Given that the proportion of hydrogenotrophic species was positively correlated with the archaeal gene abundances, we suggest that Cl concentrations primarily constrain the activity of archaea catalyzing H2 reduction of CO2. Our results show that dilution of formation waters is critical in the process of biogenic gas formation, suggesting that an engineered decrease in Cl concentrations may induce methanogenesis as a potential method to increase gas reserves in such areas in the future.

Microbial communities and their roles in the Cenozoic sulfurous oil reservoirs in the Southwestern Qaidam Basin, Western China

“…Combined with above carbon isotope values (− 54.6‰ to − 29.4‰), it can be confirmed that the natural gas was mainly derived from thermal degradation, at low-maturity stage to maturity stage. Compared with intensive negative 13 C 1 shifts in the Quaternary biogenic gas in the eastern Qaidam Basin (− 72.3 to − 60.53‰ 126 , 130 , 131 , few samples from the Yingxiongling Area in the southwest of Qaidam Basin present minor negative drifts. Therefore, the H 2 S-rich natural gas in the southwest of Qaidam Basin was derived from both thermal degradation and biodegradation, with the former of the most importance.…”

Influence of Sedimentary Environment Evolution on Fingerprint Characteristics of Methane Isotopes: A Case Study From Hangzhou Bay

“…The CD‐diagram of the δ 13 C CH4 and δD CH4 signals assigned the methanogenic pathway to CO 2 reduction (Figure 6), consistent with that the calculated fractions of CH 4 were produced by the CO 2 reduction pathway in the sediment core, with an average of 86%. Although salinity, age, and organic substrates are also presumed to be major factors controlling the relative importance of the two methanogenic pathways (Schoell, 1988; Shuai et al., 2016), the contributions of the CO 2 reduction pathway did not show a systemic difference along the depth, where the change of depth referred to the evolution of salinity and sedimentary age of the JC3 sediment core (Table S1 in Supporting Information ), suggesting that the magnitude of these changes did not affect the methanogenic pathway profoundly. A predictable change in the quality of organic matter could be inferred by the changes in sedimentary environments with varying terrestrial input (X.…”