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The inexplicable distribution of souring wells (presence of H2S gas) of the unconventional Montney Formation hydrocarbon resource (British Columbia; BC) is investigated by analysing sulphur and oxygen isotopes, coupled with XRD mineralogy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDX). The sulphur isotopic analysis indicates that the sulphur isotopic range for Triassic anhydrite (δ34S 8.9 to 20.98‰ VCDT) is the same as the H2S sulphur that is produced from the Montney Formation (δ34S 9.3 to 20.9‰ VCDT). The anhydrite in the Triassic rocks is the likely source of the sulphur in the H2S produced in the Montney Formation. The deeper Devonian sources are enriched in 34S and are not the likely source for sulphur (δ34S 17.1 and 34‰ VCDT). This is contradictory to studies on Montney Formation producers in Alberta, with heavier (34S-enriched) sulphur isotopic signatures in H2S gas of all souring Montney Formation producers. These studies conclude that deep-seated faults and fractures have provided conduits for sulphate and/or H2S gas to migrate from deeper sulphur sources in the Devonian strata. There are several wells that show a slightly heavier (34S-enriched) isotopic signature (δ34S 18 to 20‰ VCDT) within the Montney Formation H2S gas producing within close proximity to the deformation front. This variation may be due to such deep-seated faults that acted as a conduit for Devonian sulphur to migrate into the Montney Formation. Our geological model suggests the sulphate-rich fluids have migrated from the Charlie Lake Formation prior to hydrocarbon generation in the Montney Formation (BC). Sulphate has concentrated in discrete zones due to precipitation in conduits like fracture and fault systems. The model fits the observation of multi-well pads containing both sour- and sweet-producing wells indicating that the souring is occurring in very narrow and discrete zones with the Montney Formation (BC). Government agencies and operators in British Columbia should map the anhydrite-rich portions of the Charlie Lake Formation, together with the structural elements from three-dimensional seismic to reduce the risk of encountering unexpected souring. [ABSTRACT FROM AUTHOR]

The inexplicable distribution of souring wells (presence of H2S gas) of the unconventional Montney Formation hydrocarbon resource (British Columbia; BC) is investigated by analysing sulphur and oxygen isotopes, coupled with XRD mineralogy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDX). The sulphur isotopic analysis indicates that the sulphur isotopic range for Triassic anhydrite (δ34S 8.9 to 20.98‰ VCDT) is the same as the H2S sulphur that is produced from the Montney Formation (δ34S 9.3 to 20.9‰ VCDT). The anhydrite in the Triassic rocks is the likely source of the sulphur in the H2S produced in the Montney Formation. The deeper Devonian sources are enriched in 34S and are not the likely source for sulphur (δ34S 17.1 and 34‰ VCDT). This is contradictory to studies on Montney Formation producers in Alberta, with heavier (34S-enriched) sulphur isotopic signatures in H2S gas of all souring Montney Formation producers. These studies conclude that deep-seated faults and fractures have provided conduits for sulphate and/or H2S gas to migrate from deeper sulphur sources in the Devonian strata. There are several wells that show a slightly heavier (34S-enriched) isotopic signature (δ34S 18 to 20‰ VCDT) within the Montney Formation H2S gas producing within close proximity to the deformation front. This variation may be due to such deep-seated faults that acted as a conduit for Devonian sulphur to migrate into the Montney Formation. Our geological model suggests the sulphate-rich fluids have migrated from the Charlie Lake Formation prior to hydrocarbon generation in the Montney Formation (BC). Sulphate has concentrated in discrete zones due to precipitation in conduits like fracture and fault systems. The model fits the observation of multi-well pads containing both sour- and sweet-producing wells indicating that the souring is occurring in very narrow and discrete zones with the Montney Formation (BC). Government agencies and operators in British Columbia should map the anhydrite-rich portions of the Charlie Lake Formation, together with the structural elements from three-dimensional seismic to reduce the risk of encountering unexpected souring.

Scouring depends on several factors, including the water flow of artificial obstacles, sections, piers, and foundations, the disturbance of bed materials, and soil permeability. The other factors are the non-parallelism between piers and the water flow, the type of river activity (static or dynamic), and the existence of a waterfall or an obstacle that forms a waterfall in natural bed materials, causing the underlying bed materials to be washed away. This study fully investigated how the movement of a tree trunk affects a river's flow by considering different flow conditions using the artificial neural network (ANN) model. A feedforward optimal network with the error back-propagation training algorithm and sigmoid transfer functions was used for four models. To determine the number of neurons in the hidden layer, one and ten neurons were selected in the hidden layer according to verification indicators. In addition, a physical model was utilized to measure data. To verify and test the models, our data were gathered in a laboratory using the physical model. Considering the network structure of one neuron in the hidden layer, a comparison was made between dimensional and dimensionless parameter models that are effective in terms of the dimensions of the scour hole. The comparison between the results of the ANN and the measured data using nonlinear regression models demonstrated that the ANN was more accurate and capable of simulating phenomena. Additionally, R and RMSE values were between 0.93 and 0.98, as well as 0.18 and 0.013, respectively. Finally, the results related to the width, height, length, and depth of the scour revealed that the modified DOT model had the best agreement with Mahdavizadeh's measured data. [ABSTRACT FROM AUTHOR]

For the efficient production and processing of milk, it is important to control its quality indicators. Optical spectroscopy, in combination with statistical analysis methods, can be a useful method of evaluation due to its speed, non-invasiveness, and relative cheapness. This investigation is aimed at studying of the interrelations of the spectral patterns, the absorption parameters, and the photoluminescence values of cow's milk during its souring. The spectral characteristics of excitation and photoluminescence were measured on a diffraction spectrofluorometer in the range of 200–500 nm. For establishing an effective control procedure during milk souring, the most informative method is found to be the use of the excitation wavelengths of 232 nm, 322 nm, 385 nm and 442 nm. These ranges correspond to the amino acids of milk proteins, the fatty acids of milk fat, and the aromatic fragments of vitamins. When using the photoluminescence flux ratios Φ232/Φ322 and Φ385/Φ442, linearly approximated dependences on acidity can be obtained with determination coefficients of 0.88–0.94. The proposed photoluminescent method can be used as a non-destructive and fast-acting tool for monitoring the properties of milk during fermentation, as well as for the subsequent creation of a portable and inexpensive sensor based on this method. [ABSTRACT FROM AUTHOR]

Summary: For a quality assessment of milk and dairy products, the optical methods are used. In this paper, the use possibility is investigated of the optical method of photoluminescence for the milk acidity value finding out. The spectral measurements were carried out on a diffraction spectrofluorimeter in the range of 200–500 nm. The milk acidity measurement accuracy was controlled by the titrimetric method. It is established that as far as milk sours, the excitation spectra in the range of 200–500 nm decrease; but there are qualitative changes in the range of 350–500 nm. With acidity growth, the photoluminescence flux decreases if it is excited by the radiation value λe = 262 nm, grows at λe = 385 nm and decreases at λe = 442 nm. It is advisable to control the milk acidity in terms of the photoluminescence fluxes ratio Φ385/Φ442. The linear approximation of the function Φ385/Φ442(K) is statistically reliable (the determination factor R2 = 0.99). [ABSTRACT FROM AUTHOR]

Scouring depends on several factors, including the water flow of artificial obstacles, sections, piers, and foundations, the disturbance of bed materials, and soil permeability. The other factors are the non-parallelism between piers and the water flow, the type of river activity (static or dynamic), and the existence of a waterfall or an obstacle that forms a waterfall in natural bed materials, causing the underlying bed materials to be washed away. This study fully investigated how the movement of a tree trunk affects a river’s flow by considering different flow conditions using the artificial neural network (ANN) model. A feedforward optimal network with the error back-propagation training algorithm and sigmoid transfer functions was used for four models. To determine the number of neurons in the hidden layer, one and ten neurons were selected in the hidden layer according to verification indicators. In addition, a physical model was utilized to measure data. To verify and test the models, our data were gathered in a laboratory using the physical model. Considering the network structure of one neuron in the hidden layer, a comparison was made between dimensional and dimensionless parameter models that are effective in terms of the dimensions of the scour hole. The comparison between the results of the ANN and the measured data using nonlinear regression models demonstrated that the ANN was more accurate and capable of simulating phenomena. Additionally, R and RMSE values were between 0.93 and 0.98, as well as 0.18 and 0.013, respectively. Finally, the results related to the width, height, length, and depth of the scour revealed that the modified DOT model had the best agreement with Mahdavizadeh’s measured data.

Sulfide biogenesis (souring) in oil reservoirs is an extensive and costly problem. Nitrate is currently used as a souring inhibitor but often requires high concentrations and yields inconsistent results. Recently, perchlorate has displayed promise as a more potent inhibitor in lab scale studies. However, combining the two treatments to determine synergy and effectiveness in a dynamic system has never been tested. Nitrate inhibits perchlorate consumption by perchlorate reducing bacteria, suggesting that the combined treatment may allow deeper penetration of the perchlorate into the reservoir matrix. Furthermore, the metabolic intermediates of perchlorate and nitrate reduction (nitrite and chlorite, respectively) are synergistic with the primary electron acceptors for inhibition of sulfate reduction. To assess the possible synergies between nitrate and perchlorate treatments, triplicate glass columns packed with pre-soured marine sediment were flushed with media containing sulfate and an inhibitor treatment [(i) perchlorate; (ii) nitrate; (iii) perchlorate and nitrate; or (iv) none]. Internal geochemistry and microbial community changes were monitored along the length of the columns during six phases of increasing treatment concentrations. In a final phase all treatments were removed. Sulfide production decreased in all treated columns in conjunction with increased inhibitor concentrations relative to the untreated control. Interestingly, the potency of the "mixed" treatment was additive relative to the individual treatments suggesting no interaction. Microbial community analyses indicated community shifts and clustering by treatment. The mixed treatment column community's trajectory closely resembled that of the community found in the perchlorate only treatment, suggesting that perchlorate was the dominant control on the "mixed" community structure. In contrast, the nitrate and untreated column communities had unique trajectories. This study indicates that concurrent nitrate and perchlorate treatment is not more effective than perchlorate treatment alone but is more effective than nitrate treatment. As such, treatment decisions may be based on economic factors.

Biosouring results from production of H2S by sulfate-reducing microorganisms (SRMs) in oil reservoirs. H2S is toxic, corrosive, and explosive, and as such, represents a significant threat to personnel, production facilities, and transportation pipelines. Since typical oil reservoir pressures can range from 10 to 50 MPa, understanding the role that pressure plays in SRM metabolism is important to improving souring containment strategies. To explore the impact of pressure, we grew an oil-field SRM isolate, Desulfovibrio alaskensis G20, under a range of pressures (0.1-14 MPa) at 30°C. The observed microbial growth rate was an inverse function of pressure with an associated slight reduction in sulfate and lactate consumption rate. Competitive fitness experiments with randomly bar-coded transposon mutant library sequencing (RB-TnSeq) identified several genes associated with flagellar biosynthesis and assembly that were important at high pressure. The fitness impact of specific genes was confirmed using individual transposon mutants. Confocal microscopy revealed that enhanced cell aggregation occurs at later stages of growth under pressure. We also assessed the effect of pressure on SRM inhibitor potency. Dose-response experiments showed a twofold decrease in the sensitivity of D. alaskensis to the antibiotic chloramphenicol at 14 MPa. Fortuitously, pressure had no significant influence on the inhibitory potency of the common souring controlling agent nitrate, or the emerging SRM inhibitors perchlorate, monofluorophosphate, or zinc pyrithione. Our findings improve the conceptual model of microbial sulfate reduction in high-pressure environments and the influence of pressure on souring inhibitor efficacy.

Hydrogen sulfide production by sulfate reducing bacteria (SRB) is the primary cause of oil reservoir souring. Amending environments with chlorate or perchlorate [collectively denoted (per)chlorate] represents an emerging technology to prevent the onset of souring. Recent studies with perchlorate reducing bacteria (PRB) monocultures demonstrated that they have the innate capability to enzymatically oxidize sulfide, thus PRB may offer an effective means of reversing souring. (Per)chlorate may be effective by (i) direct toxicity to SRB; (ii) competitive exclusion of SRB by PRB; or (iii) reversal of souring through re-oxidation of sulfide by PRB. To determine if (per)chlorate could sweeten a soured column system and assign a quantitative value to each of the mechanisms we treated columns flooded with San Francisco bay water with temporally decreasing amounts (50, 25, and 12.5 mM) of (per)chlorate. Geochemistry and the microbial community structure were monitored and a reactive transport model was developed, Results were compared to columns treated with nitrate or untreated. Souring was reversed by all treatments at 50 mM but nitrate-treated columns began to re-sour when treatment concentrations decreased (25 mM). Re-souring was only observed in (per)chlorate-treated columns when concentrations were decreased to 12.5 mM and the extent of re-souring was less than the control columns. Microbial community analyses indicated treatment-specific community shifts. Nitrate treatment resulted in a distinct community enriched in genera known to perform sulfur cycling metabolisms and genera capable of nitrate reduction. (Per)chlorate treatment enriched for (per)chlorate reducing bacteria. (Per)chlorate treatments only enriched for sulfate reducing organisms when treatment levels were decreased. A reactive transport model of perchlorate treatment was developed and a baseline case simulation demonstrated that the model provided a good fit to the effluent geochemical data. Subsequent simulations teased out the relative role that each of the three perchlorate inhibition mechanisms played during different phases of the experiment. These results indicate that perchlorate addition is an effective strategy for both souring prevention and souring reversal. It provides insight into which organisms are involved, and illuminates the interactive effects of the inhibition mechanisms, further highlighting the versatility of perchlorate as a sweetening agent.

For the efficient production and processing of milk, it is important to control its quality indicators. Optical spectroscopy, in combination with statistical analysis methods, can be a useful method of evaluation due to its speed, non-invasiveness, and relative cheapness. This investigation is aimed at studying of the interrelations of the spectral patterns, the absorption parameters, and the photoluminescence values of cow’s milk during its souring. The spectral characteristics of excitation and photoluminescence were measured on a diffraction spectrofluorometer in the range of 200–500 nm. For establishing an effective control procedure during milk souring, the most informative method is found to be the use of the excitation wavelengths of 232 nm, 322 nm, 385 nm and 442 nm. These ranges correspond to the amino acids of milk proteins, the fatty acids of milk fat, and the aromatic fragments of vitamins. When using the photoluminescence flux ratios Φ232/Φ322 and Φ385/Φ442, linearly approximated dependences on acidity can be obtained with determination coefficients of 0.88–0.94. The proposed photoluminescent method can be used as a non-destructive and fast-acting tool for monitoring the properties of milk during fermentation, as well as for the subsequent creation of a portable and inexpensive sensor based on this method.

Oilfield souring is a detrimental effect caused by sulfate-reducing microorganisms that reduce sulfate to sulfide during their respiration process. Nitrate or nitrite can be used to mitigate souring, but may also impart a corrosion risk. Produced fluids sampled from the topside infrastructure of two floating, production, storage, and offloading (FPSO) vessels (Platform A and Platform B) were assessed for microbial corrosion under nitrate and nitrite breakthrough conditions using microcosm tests incubated at 54 °C. Microbial community compositions on each individual FPSO were similar, while those between the two FPSO vessels differed. Platform B microbial communities responded as expected to nitrate breakthrough conditions, where nitrate-reducing activity was enhanced and sulfate reduction was inhibited. In contrast, nitrate treatments of Platform A microbial communities were not as effective in preventing sulfide production. Nitrite breakthrough conditions had the strongest sulfate reduction inhibition in samples from both platforms, but exhibited the highest pitting density. Live experimental replicates with no nitrate or nitrite additive yielded the highest general corrosion rates in the study (up to 0.48 mm/year), while nitrate- or nitrite-treated fluids revealed general corrosion rates that are considered low or moderate (<0.12 mm/year). Overall, the results of this study provide a description of nitrogen- and sulfur-based microbial activities under thermophilic conditions, and their risk for MIC that can occur along fluid processing lines on FPSO topsides that process fluids during offshore oil production operations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Denitrification is a microbial process that converts nitrate (NO3–) to N2 and can play an important role in industrial applications such as souring control and microbially enhanced oil recovery (MEOR). The effectiveness of using NO3– in souring control depends on the partial reduction of NO3– to nitrite (NO2–) and/or N2O while in MEOR complete reduction of NO3– to N2 is desired. Thauera has been reported as a dominant taxon in such applications, but the impact of NO3– and NO2– concentrations, and pH on the kinetics of denitrification by this bacterium is not known. With the goal of better understanding the effects of such parameters on applications such as souring and MEOR, three strains of Thauera (K172, NS1 and TK001) were used to study denitrification kinetics when using acetate as an electron donor. At low initial NO3– concentrations (∼1 mmol L–1) and at pH 7.5, complete NO3– reduction by all strains was indicated by non-detectable NO3– concentrations and near-complete recovery (> 97%) of the initial NO3-N as N2 after 14 days of incubation. The relative rate of denitrification by NS1 was low, 0.071 mmol L–1 d–1, compared to that of K172 (0.431 mmol L–1 d–1) and TK001 (0.429 mmol L–1 d–1). Transient accumulation of up to 0.74 mmol L–1 NO2– was observed in cultures of NS1 only. Increased initial NO3– concentrations resulted in the accumulation of elevated concentrations of NO2– and N2O, particularly in incubations with K172 and NS1. Strain TK001 had the most extensive NO3– reduction under high initial NO3– concentrations, but still had only ∼78% of the initial NO3-N recovered as N2 after 90 days of incubation. As denitrification proceeded, increased pH substantially reduced denitrification rates when values exceeded ∼ 9. The rate and extent of NO3– reduction were also affected by NO2– accumulation, particularly in incubations with K172, where up to more than a 2-fold rate decrease was observed. The decrease in rate was associated with decreased transcript abundances of denitrification genes (nirS and nosZ) required to produce enzymes for reduction of NO2– and N2O. Conversely, high pH also contributed to the delayed expression of these gene transcripts rather than their abundances in strains NS1 and TK001. Increased NO2– concentrations, N2O levels and high pH appeared to cause higher stress on NS1 than on K172 and TK001 for N2 production. Collectively, these results indicate that increased pH can alter the kinetics of denitrification by Thauera strains used in this study, suggesting that liming could be a way to achieve partial denitrification to promote NO2– and N2O production (e.g., for souring control) while pH buffering would be desirable for achieving complete denitrification to N2 (e.g., for gas-mediated MEOR). [ABSTRACT FROM AUTHOR]

Microbial sulfate reduction in oil reservoirs (biosouring) is often associated with secondary oil production where seawater containing high sulfate concentrations (~28 mM) is injected into a reservoir to maintain pressure and displace oil. The sulfide generated from biosouring can cause corrosion of infrastructure, health exposure risks, and higher production costs. Isotope monitoring is a promising approach for understanding microbial sulfur cycling in reservoirs, enabling early detection of biosouring, and understanding the impact of souring. Microbial sulfate reduction is known to result in large shifts in the sulfur and oxygen isotope compositions of the residual sulfate, which can be distinguished from other processes that may be occurring in oil reservoirs, such as precipitation of sulfate and sulfide minerals. Key to the success of this method is using the appropriate isotopic fractionation factors for the conditions and processes being monitored. For a set of batch incubation experiments using a mixed microbial culture with crude oil as the electron donor, we measured a sulfur fractionation factor for sulfate reduction of -30‰. We have incorporated this result into a simplified 1D reservoir reactive transport model to highlight how isotopes can help discriminate between biotic and abiotic processes affecting sulfate and sulfide concentrations. Modeling results suggest that monitoring sulfate isotopes can provide an early indication of souring for reservoirs with reactive iron minerals that can remove the produced sulfide, especially when sulfate reduction occurs in the mixing zone between formation waters (FW) containing elevated concentrations of volatile fatty acids (VFAs) and injection water (IW) containing elevated sulfate. In addition, we examine the role of reservoir thermal, geochemical, hydrological, operational and microbiological conditions in determining microbial souring dynamics and hence the anticipated isotopic signatures.

Microbial sulfate reduction is a primary cause of oil reservoir souring. Here we show that amendment with chlorate or perchlorate [collectively (per)chlorate] potentially resolves this issue. Triplicate packed columns inoculated with marine sediment were flushed with coastal water amended with yeast extract and one of nitrate, chlorate, or perchlorate. Results showed that although sulfide production was dramatically reduced by all treatments, effluent sulfide was observed in the nitrate (10 mM) treatment after an initial inhibition period. In contrast, no effluent sulfide was observed with (per)chlorate (10 mM). Microbial community analyses indicated temporal community shifts and phylogenetic clustering by treatment. Nitrate addition stimulated Xanthomonadaceae and Rhizobiaceae growth, supporting their role in nitrate metabolism. (Per)chlorate showed distinct effects on microbial community structure compared with nitrate and resulted in a general suppression of the community relative to the untreated control combined with a significant decrease in sulfate reducing species abundance indicating specific toxicity. Furthermore, chlorate stimulated Pseudomonadaceae and Pseudoalteromonadaceae, members of which are known chlorate respirers, suggesting that chlorate may also control sulfidogenesis by biocompetitive exclusion of sulfate-reduction. Perchlorate addition stimulated Desulfobulbaceae and Desulfomonadaceae, which contain sulfide oxidizing and elemental sulfur-reducing species respectively, suggesting that effluent sulfide concentrations may be controlled through sulfur redox cycling in addition to toxicity and biocompetitive exclusion. Sulfur isotope analyses further support sulfur cycling in the columns, even when sulfide is not detected. This study indicates that (per)chlorate show great promise as inhibitors of sulfidogenesis in natural communities and provides insight into which organisms and respiratory processes are involved.

Surfactants and co-surfactants play an important role in enhanced oil recovery for they improve petroleum solubility and reduce interfacial tensions between oil, water and the rock formation. Ethanol is receiving renewed attention as potential co-surfactant because of the negative results obtained with the use of salts and alkaline substances. Sulphate-reducing bacteria (SRB) can use surfactants and co-surfactants as carbon sources and, consequently, this can increase the biological accumulation of sulphide (souring). The aim of this research is to correlate SRB activity with different concentrations of co-surfactant (ethanol) as an attempt to quantifying in which concentration such compound can potentially increase or inhibit souring. The results show that the combination of surfactant (lauryl glucoside) and co-surfactant (ethanol) can increase SRB activity to about 2.3-fold. The highest sulphate consumption rate of 591 μg l−1 h−1 was observed in experiments with 0.03% and 1.5% (v/v) of surfactant and ethanol, respectively. The experiments indicated that SRB activity is only controlled by ethanol concentrations above 6.5% (v/v). Ethanol can potentially decrease costs with the use of biocides and significantly increase oil recovery ratios. Tests with the model Desulfovibrio vulgaris were not comparable with the results obtained with the SRB consortium. [ABSTRACT FROM AUTHOR]

Highlights • NRB and SRB shared toluene, ethylbenzene, and xylene as electron donor. • 1 mM of nitrate is determined as limiting factor for souring control. • Under 1 mM of nitrate, SRB could co-exist with NRB and cause silent souring. Abstract The application of nitrate-mediated souring control has been proposed as a promising tool. However, the efficiency of this method remains controversial due to several unresolved issues, such as the determination of effective nitrate concentration, the optimal injection period, etc. In this study, we investigated the depletion of specific hydrocarbons as the electron donor for sulfate-reducing bacteria (SRB) and nitrate-reducing bacteria (NRB) by varying the nitrate concentration (1.5 mM and 4.5 mM) and injection timing (single, N s ; and multiple N m) to control souring. Based on analysis of bacterial communities, genus Arcobacter was predominant, followed by NRB of family Rhodospirillaceae , which includes Thalassospira sp. By contrast, in the condition without nitrate addition (N w/o), genus Desulfotignum was dominant. Both SRB and NRB share similar hydrocarbon preferences: toluene, ethylbenzene, and xylene. At the limiting nitrate concentration to suppress SRB activity, 1 mM, SRB could co-exist with NRB and promote a more diverse bacterial community. [ABSTRACT FROM AUTHOR]

Abstract Microbiologically active environments, like oil reservoirs, can suffer a range of problems due to the presence of sulfate-reducing microorganisms. These include, but are not limited to: H 2 S formation, souring and corrosion. To prevent biogenic sulfate reduction, nitrate can be used as an environmentally friendly alternative to biocides. However, side effects of nitrate injection are sometimes observed but not well understood. In our study, we used original water from an onshore reservoir, where a microbial enhanced oil recovery (MEOR) application is planned, and investigated the effects of nitrate addition on H 2 S generation, mineral precipitation and microbiology. We observed that nitrate did inhibit H 2 S formation in most, but not all cases. During nitrate reduction, iron and calcite minerals precipitated over short- and long-term (10 or 160 days) incubations. This was caused by a nitrate-reducing group of bacteria belonging to the family Deferribacteraceae. Using dynamic sandpack setups and numerical modeling approaches with the simulator TOUGHREACT, we observed significant reduction in permeabilities (∼44×) suggesting injectivity issues over time in case nitrate is continuously added to the reservoir. Our study shows that nitrate-dependent processes, which were described separately for pure-cultures before, are also valid for natural mixed communities present in oil fields and underlines the complex interplay of microbial metabolisms associated with those communities. Highlights • Nitrate addition to reservoir water induced iron and calcite mineral precipitation. • The minerals were microbially induced by nitrate-reducing bacteria. • Mineral precipitation during nitrate treatment led to reduction of permeability. [ABSTRACT FROM AUTHOR]

Control of microbial reduction of sulfate to sulfide in oil reservoirs (a process referred to as souring) with nitrate has been researched extensively. Nitrate is reduced to nitrite, which is a strong inhibitor of sulfate-reducing bacteria (SRB). Perchlorate has been proposed as an alternative souring control agent. It is reduced to chlorate (ClO3-) and chlorite (ClO2-), which is dismutated to chloride and O2. These can react with sulfide to form sulfur. Chlorite is also highly biocidal. Here we compared the effectiveness of perchlorate and nitrate in inhibiting SRB activity in medium containing heavy oil from the Medicine Hat Glauconitic C (MHGC) field, which has a low reservoir temperature and is injected with nitrate to control souring. Using acetate, propionate and butyrate as electron donors, perchlorate-reducing bacteria (PRB) were obtained in enrichment culture and perchlorate-reducing Magnetospirillum spp. were isolated from MHGC produced waters. In batch experiments with MHGC oil as the electron donor, nitrate was reduced to nitrite and inhibited sulfate reduction. However, perchlorate was not reduced and did not inhibit sulfate reduction in these incubations. Bioreactor experiments were conducted with sand-packed glass columns, containing MHGC oil and inoculated with an oil-grown mesophilic SRB enrichment. Once active souring (reduction of 2 mM sulfate to sulfide) was observed, these were treated with nitrate and/or perchlorate. As in the batch experiments, 4 mM nitrate completely inhibited sulfide production, while partial inhibition occurred with 1 and 2 mM nitrate, but injection of 4 mM perchlorate did not inhibit sulfate reduction and perchlorate was not reduced. The enriched and isolated PRB were unable to use heavy oil components, like alkylbenzenes, which were readily used by nitrate-reducing bacteria. Hence perchlorate, injected into a low temperature heavy oil reservoir like the MHGC, may not be reduced to toxic intermediates making nitrate a preferable souring control agent.

Sulfide biogenesis (souring) in oil reservoirs is an extensive and costly problem. Nitrate is currently used as a souring inhibitor but often requires high concentrations and yields inconsistent results. Recently, perchlorate has displayed promise as a more potent inhibitor in lab scale studies. However, combining the two treatments to determine synergy and effectiveness in a dynamic system has never been tested. Nitrate inhibits perchlorate consumption by perchlorate reducing bacteria, suggesting that the combined treatment may allow deeper penetration of the perchlorate into the reservoir matrix. Furthermore, the metabolic intermediates of perchlorate and nitrate reduction (nitrite and chlorite, respectively) are synergistic with the primary electron acceptors for inhibition of sulfate reduction. To assess the possible synergies between nitrate and perchlorate treatments, triplicate glass columns packed with pre-soured marine sediment were flushed with media containing sulfate and an inhibitor treatment [(i) perchlorate; (ii) nitrate; (iii) perchlorate and nitrate; or (iv) none]. Internal geochemistry and microbial community changes were monitored along the length of the columns during six phases of increasing treatment concentrations. In a final phase all treatments were removed. Sulfide production decreased in all treated columns in conjunction with increased inhibitor concentrations relative to the untreated control. Interestingly, the potency of the “mixed” treatment was additive relative to the individual treatments suggesting no interaction. Microbial community analyses indicated community shifts and clustering by treatment. The mixed treatment column community’s trajectory closely resembled that of the community found in the perchlorate only treatment, suggesting that perchlorate was the dominant control on the “mixed” community structure. In contrast, the nitrate and untreated column communities had unique trajectories. This study indicates that concurrent nitrate and perchlorate treatment is not more effective than perchlorate treatment alone but is more effective than nitrate treatment. As such, treatment decisions may be based on economic factors.

Hydrogen sulfide production by sulfate reducing bacteria (SRB) is the primary cause of oil reservoir souring. Amending environments with chlorate or perchlorate [collectively denoted (per)chlorate] represents an emerging technology to prevent the onset of souring. Recent studies with perchlorate reducing bacteria (PRB) monocultures demonstrated that they have the innate capability to enzymatically oxidize sulfide, thus PRB may offer an effective means of reversing souring. (Per)chlorate may be effective by (i) direct toxicity to SRB; (ii) competitive exclusion of SRB by PRB; or (iii) reversal of souring through re-oxidation of sulfide by PRB. To determine if (per)chlorate could sweeten a soured column system and assign a quantitative value to each of the mechanisms we treated columns flooded with San Francisco bay water with temporally decreasing amounts (50, 25, and 12.5 mM) of (per)chlorate. Geochemistry and the microbial community structure were monitored and a reactive transport model was developed, Results were compared to columns treated with nitrate or untreated. Souring was reversed by all treatments at 50 mM but nitrate-treated columns began to re-sour when treatment concentrations decreased (25 mM). Re-souring was only observed in (per)chlorate-treated columns when concentrations were decreased to 12.5 mM and the extent of re-souring was less than the control columns. Microbial community analyses indicated treatment-specific community shifts. Nitrate treatment resulted in a distinct community enriched in genera known to perform sulfur cycling metabolisms and genera capable of nitrate reduction. (Per)chlorate treatment enriched for (per)chlorate reducing bacteria. (Per)chlorate treatments only enriched for sulfate reducing organisms when treatment levels were decreased. A reactive transport model of perchlorate treatment was developed and a baseline case simulation demonstrated that the model provided a good fit to the effluent geochemical data. Subsequent simulations teased out the relative role that each of the three perchlorate inhibition mechanisms played during different phases of the experiment. These results indicate that perchlorate addition is an effective strategy for both souring prevention and souring reversal. It provides insight into which organisms are involved, and illuminates the interactive effects of the inhibition mechanisms, further highlighting the versatility of perchlorate as a sweetening agent.

Biosouring results from production of H2S by sulfate-reducing microorganisms (SRMs) in oil reservoirs. H2S is toxic, corrosive, and explosive, and as such, represents a significant threat to personnel, production facilities, and transportation pipelines. Since typical oil reservoir pressures can range from 10 to 50 MPa, understanding the role that pressure plays in SRM metabolism is important to improving souring containment strategies. To explore the impact of pressure, we grew an oil-field SRM isolate, Desulfovibrio alaskensis G20, under a range of pressures (0.1–14 MPa) at 30°C. The observed microbial growth rate was an inverse function of pressure with an associated slight reduction in sulfate and lactate consumption rate. Competitive fitness experiments with randomly bar-coded transposon mutant library sequencing (RB-TnSeq) identified several genes associated with flagellar biosynthesis and assembly that were important at high pressure. The fitness impact of specific genes was confirmed using individual transposon mutants. Confocal microscopy revealed that enhanced cell aggregation occurs at later stages of growth under pressure. We also assessed the effect of pressure on SRM inhibitor potency. Dose-response experiments showed a twofold decrease in the sensitivity of D. alaskensis to the antibiotic chloramphenicol at 14 MPa. Fortuitously, pressure had no significant influence on the inhibitory potency of the common souring controlling agent nitrate, or the emerging SRM inhibitors perchlorate, monofluorophosphate, or zinc pyrithione. Our findings improve the conceptual model of microbial sulfate reduction in high-pressure environments and the influence of pressure on souring inhibitor efficacy.

Crude glycerol (CG) is an abundantly available and cheap by-product from biodiesel production. Value-added applications for CG are highly wanted by industry and several processes such as the use of CG for enhanced oil recovery have been proposed. The aim of this study was to evaluate the sulfide production of sulfate-reducing bacteria (SRB) indigenous to oil reservoirs using CG as substrate. The samples of CG were obtained from a biodiesel production plant, processing castor beans, soybeans, cotton, and waste oils and fats. Growth tests were performed in Postgate medium, with different types and concentrations of CG, and a mixed inoculum of SRB isolated from the produced water of a mature oil well of Bahia (Brazil). The experiment was monitored by measuring the concentration of sulfide using a colorimetric method. The results showed that SRB grew and produced more than 250 ppm sulfide at CG concentrations of 2%. However, at CG concentrations of 3% or higher, the biogenic production of sulfide was reduced. The study demonstrates that CG will likely stimulate SRB in oil fields, whenever CG is present at lower concentrations. Maintaining CG concentrations inhibitive to SRB will not certainly be achievable throughout oil reservoirs. Dosing CG to oil fields may lead to problems associated with souring in longer terms. The utilization of CG by SRB could in turn be interesting for other biotechnological processes, e.g. metal recovery processes based on precipitation with biologically formed sulfide.

Control of microbial reduction of sulfate to sulfide in oil reservoirs (a process referred to as souring) with nitrate has been researched extensively. Nitrate is reduced to nitrite, which is a strong inhibitor of sulfate-reducing bacteria (SRB). Perchlorate has been proposed as an alternative souring control agent. It is reduced to chlorate (ClO3-) and chlorite (ClO2-), which is dismutated to chloride and O2. These can react with sulfide to form sulfur. Chlorite is also highly biocidal. Here we compared the effectiveness of perchlorate and nitrate in inhibiting SRB activity in medium containing heavy oil from the Medicine Hat Glauconitic C (MHGC) field, which has a low reservoir temperature and is injected with nitrate to control souring. Using acetate, propionate and butyrate as electron donors, perchlorate-reducing bacteria (PRB) were obtained in enrichment culture and perchlorate-reducing Magnetospirillum spp. were isolated from MHGC produced waters. In batch experiments with MHGC oil as the electron donor, nitrate was reduced to nitrite and inhibited sulfate reduction. However, perchlorate was not reduced and did not inhibit sulfate reduction in these incubations. Bioreactor experiments were conducted with sand-packed glass columns, containing MHGC oil and inoculated with an oil-grown mesophilic SRB enrichment. Once active souring (reduction of 2 mM sulfate to sulfide) was observed, these were treated with nitrate and/or perchlorate. As in the batch experiments, 4 mM nitrate completely inhibited sulfide production, while partial inhibition occurred with 1 and 2 mM nitrate, but injection of 4 mM perchlorate did not inhibit sulfate reduction and perchlorate was not reduced. The enriched and isolated PRB were unable to use heavy oil components, like alkylbenzenes, which were readily used by nitrate-reducing bacteria. Hence perchlorate, injected into a low temperature heavy oil reservoir like the MHGC, may not be reduced to toxic intermediates making nitrate a preferable souring control agent. [ABSTRACT FROM AUTHOR]

Oilfields located in western India produce crude by injection of large amounts of water during secondary oil recovery. This water is obtained from underground aquifer and contains 5 mM sulfate approximately. Sulfate present in this water is converted in to sulfide by sulfate reducing bacteria (SRB) present in the reservoir. Increased concentration of sulfide in the production fluid negatively impacts oil production and is known as reservoir souring. Most probable number and quantitative PCR enumerated 10 3 -10 8 SRB ml −1 in various field installations. Isolates from produced water in sulfate containing medium showed similarity with Desulfotomaculum , Desulfomicrobium and Thermodesulfobacterium genera. Similarly, isolates from produced water in nitrate containing medium were related to Tepidiphilus , Paenibacillaceae , Kocuria and Thauera genera. In the present study four sand packed bioreactors simulating moderately high temperature oil reservoir were used for different souring control treatments. Results revealed that continuous injection of 4 mM nitrate or 1.5 mM benzalkonium chloride (BAC) was not able to control souring. However, co-injection of 2 mM nitrate and 0.75 mM BAC completely ceased sulfide production and controlled souring. [ABSTRACT FROM AUTHOR]

Biosouring results from production of H2S by sulfate-reducing microorganisms (SRMs) in oil reservoirs. H2S is toxic, corrosive, and explosive, and as such, represents a significant threat to personnel, production facilities, and transportation pipelines. Since typical oil reservoir pressures can range from 10 to 50 MPa, understanding the role that pressure plays in SRM metabolism is important to improving souring containment strategies. To explore the impact of pressure, we grew an oil-field SRM isolate, Desulfovibrio alaskensis G20, under a range of pressures (0.1–14 MPa) at 30°C. The observed microbial growth rate was an inverse function of pressure with an associated slight reduction in sulfate and lactate consumption rate. Competitive fitness experiments with randomly bar-coded transposon mutant library sequencing (RB-TnSeq) identified several genes associated with flagellar biosynthesis and assembly that were important at high pressure. The fitness impact of specific genes was confirmed using individual transposon mutants. Confocal microscopy revealed that enhanced cell aggregation occurs at later stages of growth under pressure. We also assessed the effect of pressure on SRM inhibitor potency. Dose-response experiments showed a twofold decrease in the sensitivity of D. alaskensis to the antibiotic chloramphenicol at 14 MPa. Fortuitously, pressure had no significant influence on the inhibitory potency of the common souring controlling agent nitrate, or the emerging SRM inhibitors perchlorate, monofluorophosphate, or zinc pyrithione. Our findings improve the conceptual model of microbial sulfate reduction in high-pressure environments and the influence of pressure on souring inhibitor efficacy. [ABSTRACT FROM AUTHOR]

Nitrate injection has been widely used to minimize the production of biological hydrogen sulfide in oil and gas field industry, by controlling the growth of sulfate-reducing bacteria (SRB) chemically and biologically. This study aimed to investigate the changes in the bacterial community in response to nitrate addition used to control biological souring. Specifically, we examined the effect of nitrate addition in an artificial souring experiment, using diluted crude oil as substrate and electron donor. Desulfotignum sp. was the predominant SRB under all conditions tested. Addition of nitrate at the beginning (N 0 ) repressed the growth of SRB, as revealed by chemical and bacterial community analysis, concomitant with significant growth of the nitrate-reducing bacteria (NRB) Thalassospira sp. Nitrate addition after SRB growth (at day 28, N 28 ) successfully remediated the sulfide produced by SRB, but no significant reduction in sulfate was observed subsequently; moreover, the bacterial communities before and after nitrate addition remained identical. Isolation of Desulfotignum YB01 (D. YB01) proved the resistance of this predominant SRB in high nitrate environment. Simultaneous reduction of sulfate and nitrate by D. YB01 was also observed in this study. Therefore, the phenomenon in the N 28 experiment might be the result of the role of Arcobacter sp. which are nitrate-reducing sulfide-oxidizing bacteria, and/or the ability of Desulfotignum sp. to reduce nitrate and/or nitrite as a stress response. Thus, SRB might persist after nitrate addition, potentially causing subsequent SRB outbreaks. [ABSTRACT FROM AUTHOR]

Oil production by water injection often involves the use of makeup water to replace produced oil. Sulfate in makeup water is reduced by sulfate-reducing bacteria to sulfide, a process referred to as souring. In the MHGC field souring was caused by using makeup water with 4 mM (384 ppm) sulfate. Mixing with sulfate-free produced water gave injection water with 0.8 mM sulfate. This was amended with nitrate to limit souring and was then distributed fieldwide. The start-up of an enhanced-oil-recovery pilot caused all sulfate-containing makeup water to be used for dissolution of polymer, which was then injected into a limited region of the field. Produced water from this pilot contained 10% of the injected sulfate concentration as sulfide, but was free of sulfate. Its use as makeup water in the main water plant of the field caused injection water sulfate to drop to zero. This in turn strongly decreased produced sulfide concentrations throughout the field and allowed a decreased injection of nitrate. The decreased injection of sulfate and nitrate caused major changes in the microbial community of produced waters. Limiting sulfate dispersal into a reservoir, which acts as a sulfate-removing biofilter, is thus a powerful method to decrease souring. [ABSTRACT FROM AUTHOR]

Mesophilic and thermophilic sulfide-producing microorganisms can thrive in underground environments and cause hydrocarbon reservoir souring during energy recovery operations, and the temperature regime underground can affect the efficacy of biological control programs. In this study, we evaluated the efficacy of selected biocides using a thermophilic and a mesophilic sulfide-producing bacteria. A commonly used oilfield biocide, glutaraldehyde (Glut), and three non-traditional oil&gas field biocides, cis-1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane chloride (CTAC), 4,4-dimethyloxazolidine (DMO), and tris (hydroxymethyl) nitromethane (THNM), were used for the investigation. It was found that Glut was very effective against both mesophilic and thermophilic sulfide-producing bacteria. However, its efficacy persisted for shorter periods at 75° C compared to 35° C. Higher doses of Glut were required for complete bacterial kill over an extended period of time. As traditional preservative biocides, CTAC, DMO and THNM acted slower as compared to Glut. However, their efficacy was enhanced at elevated temperature. CTAC, DMO and THNM all showed improved performance at 75° C versus 35° C, and their efficacy persisted longer than Glut. This study highlights the potential of non-traditional oil&gas field biocides for microbial and souring control in reservoirs with challenging temperature conditions. [ABSTRACT FROM AUTHOR]

Souring, the reduction of sulfate to sulfide by sulfate-reducing bacteria (SRB) is a serious problem for the oil and gas industry. Produced waters from oil fields, injected with seawater, often contain high concentrations of acetate and sulfate, indicating a lack of activity of SRB using acetate as electron donor for sulfate reduction. Experiments with an enrichment of lactate- and sulfate-utilizing SRB from a shale oil field, indicated oxidation of lactate to acetate and subsequent oxidation of acetate in the absence of added shale oil. However, acetate was not oxidized in the presence of shale oil. In view of these results we hypothesized that acetate-utilizing SRB were inhibited by low molecular weight components present in the light shale oil, which had an American Petroleum Institute gravity (API_G) of 38°. Low molecular weight components decrease in concentration with decreasing API_G of the oil. We therefore tested the effects of diluent (83° API_G, consisting predominantly of C5-C7 alkanes), light oils (38, 41 and 46° API_G) and heavy oil (16° API_G), as well as of selected light oil components (toluene, pentane and heptane). Acetate-dependent sulfate reduction by a pure culture of Desulfobacter postgatei at 30 °C was inhibited by diluent and light oils, but not by heavy oil. Similar results were obtained with a shale gas field source water enrichment (SWE), which contained Desulfotomaculum and Desulfoarculu s as the most prominent acetate-utilizing SRB. Use of dilutions of oils in heptamethylnonane indicated that diluent inhibited acetate-utilizing SRB in SWE more strongly than light oils. Use of pure oil components indicated toluene to be more inhibitory than either pentane or heptane. GC-MS analysis confirmed that diluent had the highest concentrations of these low molecular weight components, explaining its strong inhibitory effect. Inhibition of acetate-utilizing SRB by light oil components, causing acetate accumulation in produced waters, may contribute to souring control and should be incorporated in souring control models. [ABSTRACT FROM AUTHOR]

Cucumber souring is a process mediated by a microorganisms present on the surface of cucumber fruits. Sour pickles are fresh cucumbers that have been poured over with a sodium chloride solution and various types of spices. In the present research, pre-ozonated and control cucumber fruits were subjected to the souring processes. It was observed that ozone treatment had no negative impact on the quality of the fruit before the souring process. Moreover, sour pickles after pre-ozonation had better mechanic and sensory properties than the control. [ABSTRACT FROM PUBLISHER]

The recent recognition of the environmental prevalence of perchlorate and its discovery on Mars, Earth's moon, and in meteorites, in addition to its novel application to controlling oil reservoir sulfidogenesis, has resulted in a renewed interest in this exotic ion and its associated microbiology. However, while plentiful data exists on freshwater perchlorate respiring organisms, information on their halophilic counterparts and microbial communities is scarce. Here, we investigated the temporal evolving structure of perchlorate respiring communities under a range of NaCl concentrations (1, 3, 5, 7, and 10 % wt/vol) using marine sediment amended with acetate and perchlorate. In general, perchlorate consumption rates were inversely proportional to NaCl concentration with the most rapid rate observed at 1 % NaCl. At 10 % NaCl, no perchlorate removal was observed. Transcriptional analysis of the 16S rRNA gene indicated that salinity impacted microbial community structure and the most active members were in families Rhodocyclaceae (1 and 3 % NaCl), Pseudomonadaceae (1 NaCl), Campylobacteraceae (1, 5, and 7 % NaCl), Sedimenticolaceae (3 % NaCl), Desulfuromonadaceae (5 and 7 % NaCl), Pelobacteraceae (5 % NaCl), Helicobacteraceae (5 and 7 % NaCl), and V1B07b93 (7 %). Novel isolates of genera Sedimenticola, Marinobacter, Denitromonas, Azoarcus, and Pseudomonas were obtained and their perchlorate respiring capacity confirmed. Although the obligate anaerobic, sulfur-reducing Desulfuromonadaceae species were dominant at 5 and 7 % NaCl, their enrichment may result from biological sulfur cycling, ensuing from the innate ability of DPRB to oxidize sulfide. Additionally, our results demonstrated enrichment of an archaeon of phylum Parvarchaeota at 5 % NaCl. To date, this phylum has only been described in metagenomic experiments of acid mine drainage and is unexpected in a marine community. These studies identify the intrinsic capacity of marine systems to respire perchlorate and significantly expand the known diversity of organisms capable of this novel metabolism. [ABSTRACT FROM AUTHOR]