Field Demonstration of Sulfide Removal in Reservoir Brine by Bacteria Indigenous to a Canadian Reservoir
Authors: Jenneman G.E. , Moffitt P.D. , Baja G.A. , Webb R.H. 
Published: December 2007

Abstract
A field test was performed at the Coleville field in Western Saskatchewan, Canada to evaluate the ability of indigenous bacteria to remove sulfide in produced brine. As much as 400 mg/L ammonium nitrate and 12 mg/L monosodium phosphate was co-injected upstream of two adjacent injectors over a 50 day period. Within ten days of injection, sulfide levels at the two injectors were reduced by 42 to 100% while sulfide levels at two adjacent producers declined by as much as 50 to 60% and this decline coincided with tracer breakthrough. Concentrations of indigenous sulfide-oxidizing, nitrate-reducing bacteria increased at both injectors and producers as sulfide levels decreased. Concentrations of sulfate-reducing bacteria at injectors and producers remained unchanged or decreased throughout the chemical injection period and for as long as 6 weeks following cessation of chemical injection. The results indicate that stimulation of specific indigenous bacteria through nutrient manipulation of reservoir brines has application as a cost-effective, low toxicity means to scavenge sulfide and control sulfate-reducing bacteria.

Introduction
Produced water from oil reservoirs frequently contains soluble sulfide (H2S, 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, biocides or both, whereas, protection from the corrosive nature of sulfides is often accomplished using corrosion inhibitors. Some of the problems with the use of these chemicals includes 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. and Jack et al. 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 fields as well as gas storage fields. During a microbially enhanced oil recovery field test, McInerney et al. added ammonium nitrate to injected brine at the Southeast Vasser Vertz Sand Unit in Payne County, OK and reported a 40 to 60% reduction in sulfide at three adjacent producers that was attributed to the activity of indigenous NRB. Sublette et al., 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 Westlake 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 sixfold increase in corrosion rates. More recently, Hitzman and Dennis as well as Giangiacomo and Dennis demonstrated that the application of a patented combination of nitrate, nitrite and molybdate could be used to reduce sulfide concentrations and control SRB in a process referred to as Biocompetitive Exclusion (BE).
Reservoir Description. The Coleville field (CV) is located near Kindersley in Saskatchewan, Canada.
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