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TitleMicrobial consortia controlling biogenic gas formation in the Qaidam Basin of western China
AuthorShuai, Y; Zhang, S; Grasby, S E; Hou, W; Chen, Z; Huang, L; Kui, M; Xu, Y; Wang, Y
SourceJournal of Geophysical Research, Biogeosciences vol. 121, 2017 p. 2296-2309,
Alt SeriesEarth Sciences Sector, Contribution Series 20160111
PublisherAmerican Geophysical Union
Mediapaper; on-line; digital
File formatpdf
AreaQaidam Basin; Western China; China
Subjectsfossil fuels; marine geology; biogenic gas; methane; formation water; gas fields; brine; chlorine geochemistry; chlorine; Firmicules; Methanosarcinales
Illustrationstables; plots; charts
ProgramShale-hosted petroleum ressource assesment, Geoscience for New Energy Supply (GNES)
AbstractKnowledge of what controls the activity of subsurface microbial communities is critical for assessing and managing biogenic methane resources. In this study, 19 formation water and 5 gas samples were collected at depths of 800 to 1900 m from 3 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 16s rRNA gene copies were negatively correlated with Cl concentration. The microbial community structure differed significantly depending on Cl concentrations at three gas fields. At high Cl waters (>1800 mM), the microbial community showed a halophilic signature made up of several abundant taxonomic groups within Firmicules, ?-Proteobacteria and methylotrophic Methanosarcinales. At low Cl concentration, Firmicules and hydrogenotrophic methanogens (Methanococcales and Methanomicrobiales) were dominant microbial community members. The proportion of inferred hydrogenotrophic methanogens (Methanococcales, Methanomicrobiales, and Methenobacteriales) decreased from 89% to 14% of total archaeal reads with increasing Cl concentration; in contrast, methylotrophic species (Methanosarcinales and Thermoplasmata E2) increased from 11% to 85%. Given that the proportion of inferred 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. This was further supported by stable isotope geochemistry of methane , with d13CCH4 values of -69.9 to -69.1¿ and dDCH4 values of -234.7 to -230.9¿ in Tainan fields.
Our results show that dilution of formation waters is critical in the process of biogenic gas formation. This suggests that an engineered decrease in Cl concentrations of the reservoir may induce methanogenesis as a potential method to increase gas reserves in such areas in the future.
Summary(Plain Language Summary, not published)
As part of an international collaboration GSC Scientists examined the origin of economic gas fields that are formed by microbial activity in the subsurface. These are unusual compared to most gas fields formed by thermal degradation of organic matter in rock, but can still form giants gas fields of great economic importance. A key finding of this work is the control of water salinity on the rate at which microbes generate gas. This suggests that proper management of the gas field could lead to enhanced gas generation rates by microbes, in essence a giant bioreactor forming low carbon gas resources. Further research would be warranted to test the economic potential.