Physicochemical and biological controls of sulfide accumulation in a high temperature oil reservoir
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APPLIED MICROBIAL AND CELL PHYSIOLOGY
Physicochemical and biological controls of sulfide accumulation in a high temperature oil reservoir Angeliki Marietou 1
&
Kasper U. Kjeldsen 1 & Hans Røy 1
Received: 21 May 2020 / Revised: 2 July 2020 / Accepted: 11 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In order to maintain the reservoir pressure during secondary oil production large volumes of seawater are injected into reservoirs. This practice introduces high concentrations of sulfate into the reservoir promoting the growth of sulfate-reducing microorganisms (SRM) and results in the production of an increasing volume of produced water (PW) that needs to be discharged. SRM reduce sulfate to sulfide causing reservoir souring and as a mitigation strategy nitrate is injecting along with the seawater into the reservoir. We used PW from the Halfdan oil field (North Sea) to set up microcosms to determine the best reinjection strategy in order to inhibit SRM activity and minimize the environmental impact of PW during secondary oil production. We discuss the effect of temperature, electron donor, and sulfate and nitrate availability on sulfide production and microbial community composition. Temperature and the terminal electron acceptor played a key role in shaping the microbial community of the microcosms. PW reinjection at 62 °C inhibited SRM activity due to nitrite toxicity by encouraging nitrate reduction to nitrite by thermophilic nitrate reducers, while at 74 °C we observed complete absence of any microbial activity over the course of 150 days. Key points • Temperature and the presence/ absence of nitrate shaped the microbial community structure. • Thermophilic nitrate reducers convert nitrate to ammonia with the accumulation of nitrite that inhibits sulfide production. • Nitrite inhibition is the most effective nitrate-based souring mitigation mechanisms. • The reinjection of hot produced water to oil reservoirs is a promising souring mitigation approach. Keywords Reservoir souring . Sulfate reduction . Nitrate reduction . Thermophilic . Produced water reinjection
Introduction Oil reservoirs are unique microbial habitats due to the presence of ample amounts of electron donors, high salinity, high temperature, and high pressure (Pannekens et al. 2019). In pristine oil reservoirs microbial populations are fuelled by fermentation, methanogenesis, and sulfate reduction when sulfate is present (Head et al. 2014). Oxygen and nitrate are naturally absent in subsurface oil reservoirs, but these favorable electron acceptors can be introduced during secondary oil recovery as seawater is injected into the oil reservoir in order * Angeliki Marietou [email protected] 1
Section for Microbiology, Department of Biology, Aarhus University, Aarhus, Denmark
to maintain the reservoir pressure (Gieg 2018). The reservoir rock of the Halfdan oil field in the Danish section of the North Sea is located 2000 m below the seafloor at a temperature above 80 °C (Gittel et al. 2009). The injection of w
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