Oilfield Biocide Performance in the Presence of Shale Formation Rock

Abstract Contamination of oil and gas operations by sulfate-reducing prokaryotes acid-producing prokaryotes, and facultative anaerobic prokaryotes can significantly reduce hydrocarbon quality, compromise asset integrity, and cause plugging in the formation. Complete treatment of these contaminants requires the use of biocides capable of retaining efficacy in the extreme conditions common in deep subsurface wells. This study investigates the interactions of several common oil and gas biocides with shale to determine their suitability for use in the downhole environment. Each biocide was submitted to studies analyzing (1) shale's effect on chemical stability and aqueous availability of the biocides, and (2) resulting biocidal efficacy on common facultative anaerobes. The chemical availability study was performed using high performance liquid chromatography, and the comparative biocidal efficacy study was performed using standard microbial viability assays. Due to variances in complexity of hydraulic fracture networks, the degree of adsorption was also measured as a function of shale surface area. The panel of biocides showed a variety of responses to exposure to shale. Surface-active, cationic biocides rapidly associated with shale preferentially over water, significantly reducing the availability of these compounds in the aqueous phase. Accordingly, their efficacy against planktonic bacteria substantially diminished. Across the range of shale types (surface area and reservoir source) tested, all surface-active biocides lost efficacy. Most biocides that rely on electrophilic reactivity (rather than surface activity) for efficacy against microorganisms showed little to no interaction with solid shale, and biocidal potency was not compromised. These results provide guidance for selection of biocides that will remain stable, chemically available, and ultimately efficacious in the extreme conditions of a subsurface shale reservoir.