Intensifying Stabilization and Dissolution Capacity of Polyacrylamide Emulsion Drag Reducers Using a pH-Switchable Four-Tailed Ionic Liquid Surfactant.

To balance the stability and dissolution of polyacrylamide (PAM), emulsion drag reducers dominate the successful operation of volumetric fracturing. Herein, a pH-switchable four-tailed ionic liquid surfactant (OA/Cyclen) is synthesized by oleic acid (OA) and 1,4,7,10-tetraazacyclododecane (Cyclen). The four-tailed structure of OA/Cyclen enhances the stability of the emulsion polymerization reactor and supplies enough switchable sites for triggering the intensified release of the PAM emulsion. The surface activity of OA/Cyclen varied under different pH conditions due to the interionic proton transfer between OA and Cyclen. The OA/Cyclen-stabilized monomer emulsion thus posed controllable stability. A pH-switchable PAM emulsion is produced through polymerization of this monomer emulsion, which shows a storage stability for 60 days at a pH value of 7.5. It is completely released to the aqueous solution within 20 s at a pH value of 12.03, achieving a maximum viscosity of 63 mPa·s at a polymer concentration of 0.5 wt % and a drag reduction of 61.2% at a polymer concentration of 0.05 wt %. The construction of OA/Cyclen is expected to supply an alternative for the development of drag reducer products.