Sulfide Removal in Reservoir Brine by Indigenous Bacteria

Abstract

Summary A field test was performed at the Coleville field to evaluate the ability of indigenous bacteria to remove sulfides from reservoir brine. Ammonium nitrate and sodium phosphate were injected continuously at two injectors for nearly 50 days. Sulfide levels at the two injectors declined by 42 to 100% and by as much as 50 to 60% at two adjacent producers. Concentrations of indigenous sulfide oxidizing, nitrate-reducing bacteria increased at injectors and producers while concentrations of sulfate-reducing bacteria remained unchanged or decreased slightly. Stimulation of indigenous beneficial bacteria has potential application as a cost-effective, low toxicity means to remove and control sulfides in reservoir brines. Introduction Produced water from oil reservoirs frequently contains soluble sulfide (H2 S, HS– and S2–) as a consequence of the activities of sulfate-reducing bacteria (SRB). The presence of sulfides in produced brine creates serious problems for the petroleum industry due to their toxicity, odor, corrosiveness, formation of insoluble metal sulfides, and lowering of the sales quality of produced gas. Removal and control of sulfide in reservoir brines typically involves the injection of chemicals such as sulfide scavengers and biocides, whereas, protection from the corrosive nature of sulfides is often accomplished using corrosion inhibitors. Some of the problems with the use of these chemicals include their lack of selectivity, stability, and compatibility. Additionally, many of these chemicals are expensive, toxic, and hazardous. An alternative method to remediate sulfide in reservoir brines is through selective manipulation of the indigenous bacteria. Jenneman et al.1 and Jack et al.2 demonstrated that indigenous bacteria in a sulfide-laden environment (e.g., sewage and oil field reservoir brines) could be manipulated by changing the dominant electron acceptor from sulfate to nitrate such that nitrate-reducing bacteria (NRB) oxidize the sulfide present and out-compete the SRB for common electron donors, e.g., organic acids. This approach was subsequently shown to be applicable to other produced brines from oil and gas fields3,4 as well as gas storage fields.5 During a microbially enhanced oil recovery field test, McInerney et al.6 added ammonium nitrate to injected brine at the Southeast Vasser Vertz Sand Unit in Payne County, OK and reported a 40-60% reduction in sulfide at three adjacent producers that was attributed to the activity of indigenous NRB. Sublette et al.,7 at the Salt Creek field in Wyoming, demonstrated that the non-indigenous NRB, Thiobacillus denitrificans strain F, when added to produced brine successfully removed sulfides using oxygen as an oxidant. Jack and Westlake8 reported that although the introduction of 100 ppm nitrate to an oil field brine resulted in significant changes in biofilm populations and a reduction in iron sulfide concentrations, the nitrate addition also resulted in an increase in SRB counts and a six-fold increase in corrosion rates. More recently, Hitzman and Dennis9 as well as Giangiacomo and Dennis10 successfully demonstrated that the application of a patented combination of nitrate, nitrite and molybdate 11 could be used to reduce sulfide concentrations and control SRB in a process referred to as biocompetitive exclusion. This process is designed to stimulate indigenous NRB to out-compete SRB for a common electron donor, i.e., fatty acids. Reservoir Description. The Coleville field (CV) is located near Kindersley in Saskatchewan, Canada. The field was discovered in 1951 and has been on water injection since 1958. The wells produce from the Bakken sandstone at a depth of 823 m and a bottom hole temperature of 29°C. The permeability of the formation averages between 0.49 and ?m 2 with streaks up to 3.0 ?m2. The oil is heavy, asphaltic crude with an API gravity of 13. Currently, produced water is reinjected at a rate of 4770 m3/d with less than 5% of this being make-up water from the Belly River formation. The injected brine contains total dissolved solids of less than 7500 mg/L and a pH of 7.5 at reservoir pressure. Chloride, bicarbonate and sulfate are the principal anions with sodium, calcium and magnesium the major cations. Fatty acids such as formate, acetate and propionate are below detectable levels >10 mg/L). Throughout the field, sulfide concentrations in the produced brine range from a few mg/L to greater than 200 mg/L. Souring is believed to have occurred through the activity of SRB at the time water injection was initiated. The presence of sulfides, SRB, and chlorides in the brine has contributed to a corrosive environment, which has lead to the need to apply corrosion inhibitors at the producers and a biocide at the water plant. Due to the high cost and hazardous nature of these chemicals, manipulation of indigenous bacteria through nitrate injection was evaluated as a means of removing sulfide and controlling SRB. Biological Sulfide Oxidation. During laboratory tests, the addition of 5 mM KNO3 and 100 ?M NaH 2PO4 to CV reservoir brine resulted in the complete oxidation of over 100-mg/L sulfide within 15 hours.12 This oxidation was later found to be due to the presence of a unique group of sulfide-oxidizing NRB indigenous to the CV brine.13 These NRB oxidize sulfide without the apparent requirement for organic compounds according to the equation: 5HS−+2NO3−+7H+→5S0+N2+6H2O.12 Therefore a prominent feature of this reaction involves the oxidation of sulfide to elemental sulfur via the activity of indigenous, sulfide-oxidizing NRB.

Recent Advances in Petroleum Microbiology

“…Reduction in H 2 S formation by addition of nitrate to the injection water has been reported (508,607). The beneficial effect of nitrate injection for stimulation of a competing group of nitrate-reducing bacteria has been demonstrated in several model experiments (447,508) and successful field applications (288,607). Following nitrate injection, nitrite inhibition of sulfatereducing bacteria and sulfide oxidation by nitrate-reducing bacteria have been suggested as the mechanisms for H 2 S elimination (288,447).…”

“…The beneficial effect of nitrate injection for stimulation of a competing group of nitrate-reducing bacteria has been demonstrated in several model experiments (447,508) and successful field applications (288,607). Following nitrate injection, nitrite inhibition of sulfatereducing bacteria and sulfide oxidation by nitrate-reducing bacteria have been suggested as the mechanisms for H 2 S elimination (288,447). Nitrite reductase-containing sulfate-reducing bacteria can overcome this inhibition by further reducing nitrite to ammonia (225).…”

Isolation and Characterization of Strains CVO and FWKO B, Two Novel Nitrate-Reducing, Sulfide-Oxidizing Bacteria Isolated from Oil Field Brine

“…To further demonstrate the effectiveness of nitrate in mitigating sulfides in oil field brines, a recent field test was performed at the Coleville (CV) oil field in Saskatchewan, Canada (33). Ammonium nitrate (5 mM) and sodium phosphate (0.1 mM) were added continuously to injected brine for 50 days, resulting in complete removal of sulfide at one of two injectors used in the study.…”

Efeito da aplicação de nitrato na redução biogênica de sulfeto sob diferentes concentrações iniciais de bactérias redutoras de nitrato e sulfato

“…Dados da literatura mostram que a concentração de nitrato a ser adotada para a mitigação do souring é dependente de fatores como a concentração da fonte de carbono a ser oxidada e relaciona-se intensamente com as características microbiológicas e ambientais do reservatório. Jenneman et al 7 demonstraram, em testes de campo, que a aplicação de 207 mg L -1 de NO 3 -foi suficiente para a remoção total de sulfeto; enquanto a inibição de souring com aplicações de 80 mg L -1 de NO 3 -e a remoção completa de H 2 S com dosagens de 100 mg L -1 de NO 3 -é reportada por outros autores. 9 Londry e Sulfita, 25 em testes de laboratório, propuseram dosagens bem mais elevadas, da ordem de 3100 mg L -1 de NO 3 -para reduzir em 90% a redução de sulfato.…”

“…A reutilização da água produzida constitui uma alternativa de manejo, pois sua disposição acarreta sérios danos ambientais, sendo este procedimento adotado em locais em que a legislação ambiental é mais restritiva, como nos campos do Mar do Norte. [7][8][9][10][11] A acidificação de reservatórios, associada à recuperação secundária do petróleo, pode resultar em corrosão, obstrução dos poços injetores e produtores pela deposição de FeS, redução da produtividade dos poços e da qualidade do petróleo produzido. 2,4,10 Todos estes problemas justificam a importância de se desenvolver estudos para o controle ou a prevenção do souring em reservatórios de petróleo.…”