Implications of Limited Thermophilicity of Nitrite Reduction for Control of Sulfide Production in Oil Reservoirs

Abstract

Nitrate reduction to nitrite in oil fields appears to be more thermophilic than the subsequent reduction of nitrite. Concentrated microbial consortia from oil fields reduced both nitrate and nitrite at 40 and 45°C but only nitrate at and above 50°C. The abundance of the nirS gene correlated with mesophilic nitrite reduction activity. Thauera and Pseudomonas were the dominant mesophilic nitrate-reducing bacteria (mNRB), whereas Petrobacter and Geobacillus were the dominant thermophilic NRB (tNRB) in these consortia. The mNRB Thauera sp. strain TK001, isolated in this study, reduced nitrate and nitrite at 40 and 45°C but not at 50°C, whereas the tNRB Petrobacter sp. strain TK002 and Geobacillus sp. strain TK003 reduced nitrate to nitrite but did not reduce nitrite further from 50 to 70°C. Testing of 12 deposited pure cultures of tNRB with 4 electron donors indicated reduction of nitrate in 40 of 48 and reduction of nitrite in only 9 of 48 incubations. Nitrate is injected into high-temperature oil fields to prevent sulfide formation (souring) by sulfate-reducing bacteria (SRB), which are strongly inhibited by nitrite. Injection of cold seawater to produce oil creates mesothermic zones. Our results suggest that preventing the temperature of these zones from dropping below 50°C will limit the reduction of nitrite, allowing more effective souring control. IMPORTANCENitrite can accumulate at temperatures of 50 to 70°C, because nitrate reduction extends to higher temperatures than the subsequent reduction of nitrite. This is important for understanding the fundamentals of thermophilicity and for the control of souring in oil fields catalyzed by SRB, which are strongly inhibited by nitrite.

Use of Acetate, Propionate, and Butyrate for Reduction of Nitrate and Sulfate and Methanogenesis in Microcosms and Bioreactors Simulating an Oil Reservoir

“…Excess amounts of electron donors are expected in oil fields, and transient inhibition was indeed demonstrated in the MHGC field, when injection water with 1 mM sulfate was continuously amended with 2 mM nitrate (3,4). Interestingly, competitive exclusion applies in the presence of excess electron donors at high (Ͼ50°C) temperatures, because nitrate reduction stops at nitrite under these conditions (35). Nitrite is a very strong and specific SRB inhibitor (38) which targets sulfide-producing dissimilatory sulfite reductase (Dsr).…”

Halophilic Methylotrophic Methanogens May Contribute to the High Ammonium Concentrations Found in Shale Oil and Shale Gas Reservoirs

“…DNAs were amplified using a two-step PCR process with Illumina Miseq non-barcoded primers 926Fi5 and 1392RiF (An et al, 2017) for the first PCR. PCR was performed for 3 min at 95 • C, followed by 25 cycles of 30 s at 95 • C, 45 s at 55 • C, and 2 min at 72 • C, and then 10 min at 72 • C. For the second PCR (10 cycles), forward primer P5-S50X-OHAF and reverse primer P7-N7XX-OHAF were used (Fida et al, 2016;An et al, 2017). The final PCR product was purified and quantified using the same procedures as above and sent for Illumina Miseq sequencing at the University of Calgary.…”

“…Hence, there are multiple incentives for controlling microbial activities in shale gas reservoirs. Creating multiple environments by changing salinity and temperature through injection of cold fresh water and by storing produced water above ground complicates the problem of microbial control, e.g., when temperature and/or salinity are kept high nitrate-reducing bacteria (NRB) reduce nitrate only to nitrite, which is a powerful SRB inhibitor (Fida et al, 2016;An et al, 2017). Hence, SRB control with nitrate is easier if environments with low salinity and temperature are not allowed to emerge in shale gas or shale oil operations.…”

Life in deep subsurface

“…Physiological studies reveal that famine could be the most common lifestyle in deep subsurface [30], communities being prone to reactivation when amended [31].…”