Microbial fouling in oil and gas stimulation has been shown to cause a multitude of problems, including formation plugging, hydrogen sulfide (H2S) exposure, microbial induced corrosion, and well souring, all of which can have deleterious effects on well production and quality of oil and gas. In order to determine the most appropriate biocide to mitigate these issues, end users must take many factors into consideration, such as basic biocidal activity, fluid composition, environmental compatibility, and user safety. Additionally, with an increased reliance on recycling and reuse of flowback water, microbiological control in stimulation has become more challenging given the current market push for reduced use of fresh water. Recycled or higher solids waters can carry more bacteria, thus require higher treatment rates when using conventional non-oxidizing biocides. This paper presents a biguanide polyammonium-based blend biocide composed of polyhexamethylene biguanide and a polyquaternary ammonium compound that was designed to meet the performance and market challenges in the current oil and gas stimulation dynamic. Results showed that the biguanide polyammonium-based blend provided quick and persistent biocidal activity against a range of bacteria, including acid producing and sulfate reducing bacteria, at low concentrations, indicating effective biocidal capability. The biguanide polyammonium-based blend was also compatible with additives found in typical oil and gas stimulation fluid packages and worked over a broad range of pH, TDS, and temperatures, indicating broad fluid and environmental compatibility across oil and gas stimulation applications. In addition, there are no open pour restrictions, demonstrating that the biguanide polyammonium-based blend is safer to handle than other biocides. These results were verified in multiple oil and gas stimulation field assessments confirming the validity of the laboratory bench top evaluation.
Key words: biocide, non-oxidizing biocide, oil and gas, hydraulic fracturing, stimulation, chemical compatibility, hydrothermal stability, biguanide polyammonium-blend, BPAB, total dissolved solids