AAPG Foundation 2019 Grants-in-Aid Projects

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Diversity and function of petroleum-degrading microbes in subsurface environments


Subsurface petroleum environments, which include reserves of crude oil, natural gas, and unconventional gas systems, are important frontiers of deep biosphere and energy development research due recent discoveries of diverse microbial communities indigenous to petroleum reservoirs1. These strictly anaerobic microbial communities degrade petroleum compounds as a carbon source for their metabolic activities2. Biodegraded oils comprise >50% of the global inventory3, and their more dense, viscous, and acidic properties complicate extraction and purification processes4. In the petroleum-rich North West Shelf (NWS) region of Western Australia, biodegraded oils comprise a significant portion of remaining reserves5. Abundant geochemical studies have been carried out on NWS biodegraded oils6,7, but no microbial ecology data of those same reservoirs currently exist. Petroleum compounds are degraded by syntrophic microbial consortia8, from which methane (CH4) is discharged as a terminal product9,10. This study aims to characterize microbial diversity and metabolic functions that relate to biodegradation in petroleum reservoirs, the results of which may be applied toward industrial efforts in secondary oil production and methane production. Metagenomic analysis of collected well samples determined that bacteria comprised >98% of the microbial community, but predominance shifted toward methane-producing archaea after several months of anaerobic incubation at ambient reservoir temperatures. The incubations were also inoculated with various crude oils and hydrocarbon-derived substrates to stimulate microbial activity and biodegradation. Preliminary gas compositional analysis showed presence of CO2, CH4, and other n-paraffin gases, and further work will focus on analysing changes in microbial community and biodegradation over time.