Physicochemical and biological controls of sulfide accumulation in a high temperature oil reservoir

Nitrate and oxygen significantly changed the abundance rather than structure of sulphate-reducing and sulphur-oxidising bacteria in water retrieved from petroleum reservoirs

Sulphate-reducing bacteria (SRB) are the main culprits of microbiologically influenced corrosion in water-flooding petroleum reservoirs, but some sulphur-oxidising bacteria (SOB) are stimulated when nitrate and oxygen are injected, which control the growth of SRB. This study aimed to determine the distributions of SRB and SOB communities in injection-production systems and to analyse the responses of these bacteria to different treatments involving nitrate and oxygen. Desulfovibrio, Desulfobacca, Desulfobulbus, Sulfuricurvum and Dechloromonas were commonly detected via 16S rRNA gene sequencing. Still, no significant differences were observed for either the SRB or SOB communities between injection and production wells. Three groups of water samples collected from different sampling sites were incubated. Statistical analysis of functional gene (dsrB and soxB) clone libraries and quantitative polymerase chain reaction showed that the SOB community structures were more strongly affected by the nitrate and oxygen levels than SRB clustered according to the sampling site; moreover, both the SRB and SOB community abundances significantly changed. Additionally, the highest SRB inhibitory effect and the lowest dsrB/soxB ratio were obtained under high concentrations of nitrate and oxygen in the three groups, suggesting that the synergistic effect of nitrate and oxygen level was strong on the inhibition of SRB by potential SOB.

Sulfur-oxidizing bacteria (SOB) and sulfate-reducing bacteria (SRB) in oil reservoir and biological control of SRB: a review

Sulfur-oxidizing bacteria (SOB) and sulfate-reducing bacteria (SRB) inhabit oilfield production systems. Sulfur oxidation driven by SOB and dissimilatory sulfate reduction driven by SRB play important roles in sulfur cycle of oil reservoirs. More importantly, hydrogen sulfide produced by SRB is an acidic, flammable, and smelly toxic gas associated with reservoir souring, corrosion of oil-production facilities, and personnel safety. Effective control of SRB is urgently needed for the oil industry. This depends on an in-depth understanding of the microbial species that drive sulfur cycle and other related microorganisms in oil reservoir environments. Here, we identified SOB and SRB in produced brines of Qizhong block (Xinjiang Oilfield, China) from metagenome sequencing data based on reported SOB and SRB, reviewed metabolic pathways of sulfur oxidation and dissimilatory sulfate reduction, and ways for SRB control. The existing issues and future research of microbial sulfur cycle and SRB control are also discussed. Knowledge of the distribution of the microbial populations, their metabolic characteristics and interactions can help to develop an effective process to harness these microorganisms for oilfield production.

Bio-augmentation with dissimilatory nitrate reduction to ammonium (DNRA) driven sulfide-oxidizing bacteria enhances the durability of nitrate-mediated souring control

Biological souring (producing sulfide) is a global challenge facing anaerobic water bodies, especially the oil reservoir fluids. Nitrate injection has demonstrated great potential in souring control, and dissimilatory nitrate reduction to ammonium (DNRA) bacteria was proposed to play crucial roles in the process. How to durably control souring with nitrate amendment, however, remains undiscovered. Herein, Gordonia sp. TD-4, a DNRA-driven sulfide-oxidizing bacterium, was used to elucidate the effects of bio-augmentation with DNRA bacteria on the durability of nitrate-mediated souring control. The results revealed that nitrate amendment combined with bio-augmentation with TD-4 after souring could effectively control souring and enhance the durability of nitrate-mediated souring control, while nitrate amendment before souring failed to persistently control souring. Nitrate amendment before and after souring resulted in different evolution dynamics of nitrate-reducing bacteria. Denitrifying bacteria were enriched in reactors amended with nitrate before souring or in dissolved sulfide exhausted reactors amended with nitrate after souring. The heterotrophic denitrifying activity of denitrifying bacteria, however, decreased the durability of nitrate-mediated souring control. Comparative and functional genomics analysis identified potential niche adaptation mechanisms (autotrophic and heterotrophic nitrate/nitrite reduction, including DNRA and denitrification) of predominant SRB in nitrate-amended environments, which were responsible for the rapid resumption of sulfide accumulation after the depletion of nitrate and nitrite. Pulsed injection of nitrate combined with bio-augmentation with DNRA-driven sulfide-oxidizing bacteria was proposed as a potential method to enhance the durability of nitrate-mediated souring control. The findings were innovatively applied to simultaneous bio-demulsification and souring control of emulsified and sour produced water from the petroleum industry.

Importance of thermodynamics dependent kinetic parameters in nitrate-based souring mitigation studies

Souring is the unwanted formation of hydrogen sulfide (H₂S) by sulfate-reducing microorganisms (SRM) in sewer systems and seawater flooded oil reservoirs. Nitrate treatment (NT) is one of the major methods to alleviate souring: The mechanism of souring remediation by NT is stimulation of nitrate reducing microorganisms (NRM) that depending on the nitrate reduction pathway can outcompete SRM for common electron donors, or oxidize sulfide to sulfate. However, some nitrate reduction pathways may challenge the efficacy of NT. Therefore, a precise understanding of souring rate, nitrate reduction rate and pathways is crucial for efficient souring management. Here, we investigate the necessity of incorporating two thermodynamic dependent kinetic parameters, namely, the growth yield (Y), and F_T, a parameter related to the minimum catabolic energy production required by cells to utilize a given catabolic reaction. We first show that depending on physiochemical conditions, Y and F_T for SRM change significantly in the range of [0-0.4] mole biomass per mole electron donor and [0.0006-0.5], respectively, suggesting that these parameters should not be considered constant and that it is important to couple souring models with thermodynamic models. Then, we highlight this further by showing an experimental dataset that can be modeled very well by considering variable F_T. Next, we show that nitrate based lithotrophic sulfide oxidation to sulfate (lNRM₃) is the dominant nitrate reduction pathway. Then, arguing that thermodynamics would suggest that S° consumption should proceed faster than S⁰ production, we infer that the reason for frequently observed S⁰ accumulation is its low solubility. Last, we suggest that nitrate based souring treatment will suffer less from S⁰ accumulation if we (i) act early, (ii) increase temperature and (iii) supplement stoichiometrically sufficient nitrate.

Sulfate reducing microorganisms in high temperature oil reservoirs

High temperature reservoirs offer a window into the microbial life of the deep biosphere. Sulfate reducing microorganisms have been recovered from high temperature oil reservoirs around the globe and characterized using culture-dependent and culture-independent approaches. The activities of sulfate reducers contribute to reservoir souring and hydrocarbon degradation among other attracting considerable interest from the oil industry for the last 100 years. The extremes of temperature and pressure shape the activities and distribution of sulfate reducing bacteria and archaea in high temperature reservoirs. This chapter will attempt to summarize the key findings on the diversity and activities of sulfate reducing microorganisms in high temperature reservoirs.