Enhanced Stability and Release Efficiency of an Emulsion Drag Reducer Using a pH-Responsive Rigid Piperazine Ring Gemini Surfactant

The growing demand for petroleum has intensified the pressure on conventional resources, driving exploration into unconventional reservoirs. Polyacrylamide (PAM) emulsion drag reducers can suppress fracturing fluid turbulence and improve reservoir stimulation, but their poor dissolution efficiency remains a key obstacle to widespread application. Herein, a pH-responsive Gemini surfactant (PA/OA) featuring a rigid piperazine ring as the hydrophilic headgroup was synthesized using piperazine (PA) and oleic acid (HOA). The PA/OA-stabilized monomer emulsion exhibited excellent stability for over 50 days at pH 7.0, enabling the successful inverse emulsion polymerization of PAM. The introduction of the piperazine ring and double hydrophobic tails enhances the molecular rigidity to promote a tight arrangement at the oil-water interface, thereby reinforcing the interfacial film and enhancing the interfacial activity. The surface activity of PA/OA varied at different pH conditions due to the interionic proton transfer between OA and PA. The pH-responsive ionic bonds in PA/OA facilitate rapid release of emulsion drag reducers, with most released within 30 s at pH = 10.0, and achieve a drag reduction rate of 68% at a concentration of 0.05 wt %. The PA/OA-stabilized emulsion effectively reconciled the conflict between long-term storage stability and rapid release performance encountered in single-chain-responsive surfactant systems.