Optimal Treatment and Reuse of Flowback and Produced Water: Selective Removal of Problematic Cations for Stability of Friction Reducers

The oil and gas industry has been considering treatment and reuse of produced water for hydraulic fracturing of unconventional reservoirs to reduce environmental footprints and economic costs. In this paper, we studied the compatibility of Duvernay flowback and produced water (FPW) with anionic polyacrylamide-based friction reducer (FR) sample. Shear viscosity, particle size distribution, and viscoelasticity measurements were conducted to assess the performance of FR in both untreated and treated PW using Na₂CO³. The experimental results indicate that Ca²⁺ and Mg²⁺ are removed by up to 92.89% and almost 100%, respectively, at pH value of 11.5±0.10 and temperature of 80°C. The measured viscosity profile of FR in treated and untreated FPW are similar, suggesting that removing Ca²⁺, Mg²⁺, and Fe²⁺ from FPW does not significantly increase the viscosity of slickwater. The viscoelastic properties of slickwater are found to be significantly increased when Ca²⁺ concentration is decreased to 933.10 mg/L, and the size distribution of FR molecules become more uniform when the Ca²⁺ and Mg²⁺ concentrations are reduced to 1670.7 mg/L and <0.01 mg/L, respectively. Overall, a minimum Ca²⁺ concentration of 1670.7 mg/L and Mg²⁺ concentration of <0.01 mg/L are needed to prepare stable slickwater with Duvernay FPW.

The extraction of oil from low-permeability reservoirs, such as shale and tight sandstones, poses significant challenges due to the restricted flow of oil and gas through the formation. Hydraulic fracturing, commonly known as "fracking" is a widely accepted technique in the petroleum industry that is used to improve the permeability and productivity of such reservoirs (Guo et al., 2022). The hydraulic fracturing process entails injecting a mixture of fluids at high pressure into the wellbore, including water, proppants, and various additives such as friction reducers, surfactant, and biocides. The proppants help maintain the fractures’ aperture, while the friction reducers and surfactant additives mitigate friction and biocide prevents bacterial growth that may clog the fractures (Barati & Liang, 2014).