PH-switchable W/O drag reducer emulsions based on dynamic covalent stabilizers for efficient stabilization and rapid dissolution of drag reducers

Abstract

As the global emphasis on shale oil extraction grows, there is a rising demand for slickwater fracturing fluids for reservoir stimulation. Polyacrylamide drag reducers plays a crucial role in slickwater and are available in two primary forms: powder and emulsion. Powder-based drag reducers suitable for long-term transportation and storage, but increasing their dissolution rate remains a challenge. While emulsion-based drag reducers are valued for the efficient dissolution facilitated by hydrophilic phase-inversion surfactants, the incorporation of the surfactants compromise the stability of W/O emulsions. In this work, an imine-functionalized pH-switchable stabilizer was synthesized, and the W/O emulsion constructed with the stabilizer underwent demulsification at a pH of 4.9. The pH-switchable emulsion system was optimized, and inverse emulsion polymerization using the stable monomer emulsion was performed for preparing pH-switchable drag reducer emulsions. The drag reducer emulsion features remarkable resistance to instability even after 30 days of storage owing to the absence of phase-inversion surfactants. The imine bond on the stabilizer was cleaved in acid solution, allowing the switchable drag reducer emulsion to be rapidly released and dissolved in water at pH 2.75, boasting an impressive dissolution rate of only 150 s. Furthermore, the pH-switchable drag reducer emulsion demonstrated effective drag-reduction performance, achieving a drag-reduction rate as 73 % at a concentration of 0.06 wt%. The pH-switchable drag reducer emulsion effectively resolves the conflict between rapid dissolution and efficient stabilization of drag reducer, thus offering potential improvements in the formulation process of slickwater and the efficiency of shale oil development.