Biocides play a critical role in the exploitation of low permeability oil and gas formations via hydraulic fracturing by protecting the integrity of fracturing fluids and preventing the souring of the wells. Traditionally, biocide selection for a well is determined though a limited battery of tests used to evaluate initial biocidal activity and biocide effects on performance of the fracturing fluid. This paper presents the results of an enhanced biocide selection evaluation that extends past the traditional selection process to include stability and performance with a larger range of fracturing additives, environmental conditions, and secondary biocidal properties. Results show when using this enhanced process, a more accurate view of performance advantages and limitations of commonly used biocides emerge. In the expanded laboratory experiments, limitations with stability and performance were better elucidated with biocides such as 2,2-dibromo-3-nitrilopropionamide, glutaraldehyde, and glutaraldehyde/quaternary ammonium blends. Whereas with phosphonium polyammonium blend-based biocide, additional performance advantages were revealed. Comparative field assessments confirmed the validity and benefit of this expanded biocide evaluation for fracturing applications.
Key words: biocide, non-oxidizing, oil and gas, hydraulic fracturing, stimulation, hydrothermal stability, compatibility, oxidative breaker, phosphonium polyammonium blend, PPAB