Environmental Self-Enhancement in PAM/SA Hydrogels: A Strategy for Deep Conformance Control in Heterogeneous Reservoirs

This study systematically investigates the swelling, time-dependent mechanical decay, and degradation of polyacrylamide (PAM)-based gels under simulated high-temperature reservoir conditions. A Ca2+-induced “environmentally self-enhancing” PAM/sodium alginate (SA) composite gel was designed to alleviate the pronounced performance decline caused by swelling and degradation. In this system, progressive cross-linking between SA and Ca2+ in formation water leads to the formation of an interpenetrating network (IPN), which contributes to improved structural stability. Experimental results indicate that incorporating 1.5% SA into a 20% PAM gel increases the swelling strength by a factor of 6.7, while the three-month strength retention improves from 14% to 50%. The composite gel also shows enhanced fatigue resistance and a delayed swelling response. In addition, PAM/SA microspheres prepared via inverse emulsion polymerization exhibit improved mechanical robustness after Ca2+ cross-linking, with the elastic modulus increasing by 36%. Core flooding experiments show that PAM/SA microspheres are able to gradually form stable plugging structures in porous media. After 7 days of swelling, the plugging ratio increases by 23% and the oil displacement efficiency improves by 3% compared with PAM microspheres. Microfluidic visualization further indicates that swollen microspheres form reconfigurable deposits within pore throats, which suppress preferential flow. Both the plugging pressure and the frequency of pressure fluctuations increase noticeably, and the displacement efficiency rises by 4%, reflecting enhanced flow field regulation. Overall, this study provides cross-scale experimental evidence for the environmentally induced strengthening mechanism of PAM/SA gels and suggests their potential application in deep conformance control.