ABSTRACT

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.

INTRODUCTION

Advanced stimulation techniques, such as hydraulic fracturing of horizontal wells, have made the exploitation of low permeability oil and gas formations possible in recent years. Water, sand, and various chemical additives are injected into the ground to fracture open a formation and unlock the oil and gas. Biocides play a critical role both during and after the fracturing process protecting the integrity of the fracturing fluid and preventing souring of the well, respectively. Although biocides play a critical role in the overall effectiveness of a frac job, the traditional selection process is usually limited to laboratory tests to evaluate their biocidal activity and effect on the performance of the frac fluid, which doesn’t tell the entire story.1

We report here on an enhanced selection process that takes biocide evaluation a step further by considering additional factors that affect biocide stability and performance in the presence of a wide range of frac additives, environmental conditions, and secondary properties of the biocide. The results indicate that when the enhanced selection process is used to evaluate biocides for frac applications, performance limitations of the commonly used frac biocides, such as DBNPA, glutaraldehyde, and glutaraldehyde/quaternary ammonium blends, become apparent while a biocide based on a phosphonium polyammonium blend stands out as having superior applicability and performance in frac applications. Results from successful field applications of the phosphonium polyammonium blend have confirmed the usefulness of this biocide and the benefit of the enhanced frac biocide selection process.

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