Effective microbiological control is a vital component of a successful fracturing stimulation. As the development of tight gas, shale and other unconventional resources increased, innovative hydraulic-fracture designs including linear gel, slickwater and hybrid treatments have grown in popularity. These designs often require significant volumes of water that originate from rivers, lakes and ponds as well as produced and flowback water. Frequently, these sources are infested with aerobic and anaerobic bacteria that can lead to degradation of fracturing chemicals, microbially influenced corrosion, hydrogen sulfide generation and other production problems.
Control of bacterial growth may be accomplished through the use of biocides. Glutaraldehyde and quaternary ammonium-based surfactants are two of the most prevalent chemistries used in Canadian fracture fluids. Because of the inherent toxicity of biocide additives, the primary goal is to design a program that minimizes chemical usage while matching the total demand necessary to control and manage bacteria. Controlling bacteria means not only an effective kill at the surface before use, but also maintaining this control long term while the fracturing fluids are in contact with the reservoir. Oxidative biocides are an attractive treatment option because of the rapid kinetics of disinfection, the ability to provide excellent control of bacteria populations and the short residual lifetimes that do not persist in the flowback beyond a few days or hours. In addition, oxidizing biocides enable a concomitant reduction in the quantity of preservative biocides required to achieve long-term control.
This paper reviews the efficacy of a chlorine dioxide-based biocide program used in hydraulic fracturing in central Alberta, Canada. The results of the bacteria enumerated from job site samples are presented, along with application methodologies and program design. It was observed that chlorine dioxide combined with a low concentration of preservative biocide can provide enhanced efficacy and reduce total chemical demand compared to conventional biocide treatments.
Chlorine dioxide is approved for use as a biocide for hydraulic fracturing by the Canadian Pest Management Regulatory Authority (PMRA). Chlorine dioxide provides new opportunities to build more efficient hydraulic fracturing biocide programs.