Electrostatically Enhanced Swelling Stability and Mechanics of Polyzwitterionic P(AM/AMPS/DMC) Hydrogels for High-Temperature and High-Salinity Reservoir Environment

Conventional polyacrylamide (PAM) gel profile control agents exhibit significant degradation in swelling capacity and mechanical strength under high-temperature and high-salinity reservoir conditions. This study proposes an electrostatic enhancement strategy to develop a polyzwitterionic Poly(acrylamide/2-acrylamido-2-methylpropanesulfonic acid/methacrylatoethyl trimethyl ammonium chloride) hydrogel (PASD). The hydrogel combines a superior swelling performance and mechanical strength. The external salt ions exert electrostatic shielding on the swelling-equilibrated PASD with an increase in salinity, which weakens electrostatic attraction between polymer chains to facilitate chain extension, triggering a secondary swelling increase from 216 to 230%. Moreover, the reversible ion-pair dissociation–recombination mechanism between −SO3– and −N+(CH3)3 enables effective stress transfer and energy dissipation. As a result, the swollen PASD hydrogel exhibits a compressive strength 4 times higher than that of the PAM gel and superior cyclic compression resistance for up to 500 cycles. PASD avoids volumetric shrinkage under elevated salinity and even undergoes secondary swelling. Meanwhile, it shows enhanced mechanical properties, demonstrating exceptional environmental adaptability. PASD microgels synthesized via this approach serve as efficient profile control agents in harsh environments, retaining 68% water-plugging efficiency after 10 days─1.7 times the efficiency of PAM microgels. This study proposes a simple and effective electrostatic interaction-based strategy to develop hydrogels with enhanced swelling stability and mechanical properties for a superior long-term plugging performance.