Understanding Microbial Community Dynamics in Up-Flow Bioreactors to Improve Mitigation Strategies for Oil Souring

Avishek Dutta; Ben Smith; Thomas Goldman; Leanne Walker; Matthew Streets; Bob Eden; Reinhard Dirmeier; Jeff S Bowman

doi:10.3389/fmicb.2020.585943

Understanding Microbial Community Dynamics in Up-Flow Bioreactors to Improve Mitigation Strategies for Oil Souring

Front Microbiol. 2020 Dec 3:11:585943. doi: 10.3389/fmicb.2020.585943. eCollection 2020.

Authors

Avishek Dutta¹, Ben Smith², Thomas Goldman³, Leanne Walker⁴, Matthew Streets⁴, Bob Eden⁴, Reinhard Dirmeier³, Jeff S Bowman^{1

5}

Affiliations

¹ Integrative Oceanography Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, United States.
² BP Upstream Technology, London, United Kingdom.
³ BP Biosciences Center, San Diego, CA, United States.
⁴ Rawwater Engineering Company Ltd., Culcheth, United Kingdom.
⁵ Center for Microbiome Innovation, University of California, San Diego, La Jolla, CA, United States.

Abstract

Oil souring occurs when H₂S is generated in oil reservoirs. This not only leads to operational risks and health hazards but also increases the cost of refining crude oil. Sulfate-reducing microorganisms are considered to be the main source of the H₂S that leads to oil souring. Substrate competition between nitrate-reducing and sulfate-reducing microorganisms makes biosouring mitigation via the addition of nitrate salts a viable strategy. This study explores the shift in microbial community across different phases of biosouring and mitigation. Anaerobic sand-filled columns wetted with seawater and/or oil were used to initiate the processes of sulfidogenesis, followed by mitigation with nitrate, rebound sulfidogenesis, and rebound control phases (via nitrate and low salinity treatment). Shifts in microbial community structure and function were observed across different phases of seawater and oil setups. Marine bacterial taxa (Marinobacter, Marinobacterium, Thalassolituus, Alteromonas, and Cycloclasticus) were found to be the initial responders to the application of nitrate during mitigation of sulfidogenesis in both seawater- and oil- wetted columns. Autotrophic groups (Sulfurimonas and Desulfatibacillum) were found to be higher in seawater-wetted columns compared to oil-wetted columns, suggesting the potential for autotrophic volatile fatty acid (VFA) production in oil-field aquifers when seawater is introduced. Results indicate that fermentative (such as Bacteroidetes) and oil-degrading bacteria (such as Desulfobacula toluolica) play an important role in generating electron donors in the system, which may sustain biosouring and nitrate reduction. Persistence of certain microorganisms (Desulfobacula) across different phases was observed, which may be due to a shift in metabolic lifestyle of the microorganisms across phases, or zonation based on nutrient availability in the columns. Overall results suggest mitigation strategies for biosouring can be improved by monitoring VFA concentrations and microbial community dynamics in the oil reservoirs during secondary recovery of oil.

Keywords: biosouring; marine microbes; microbial community; mitigation; volatile fatty acids.