Core–Shell PAM@PVA Hydrogel with Enhanced Plugging Strength and Controllable Degradation for Petroleum Exploitation

Although polyacrylamide-based hydrogel exhibits excellent swelling and migration properties, it is more desirable for hydrogels with high compressive strength, flexible deformation, and rapid degradability for petroleum extraction. Herein, the core–shell structure PAM@PVA composite hydrogel achieves enhanced plugging strength through the Hofmeister effect of the PVA core and rapid degradability through the self-degrading ester bond of the flexible PAM shell, resulting in macroscopic and microscale hydrogels for oilfield fracturing and deep profile control. After the PVA network forms intramolecular hydrogen bonds by freeze–thaw and soaking in Na2SO4 brine, the PAM@PVA hydrogels reach a compressive strength of 5.62 MPa at 60% strain, which is three times that of PAM hydrogels. In the simulated fracturing plugging pressure resistance test, the macroscopic PAM@PVA hydrogels with the soft shell and hard core achieve a plugging strength of 2.48 MPa, effectively preventing migration during the plugging perforation process. At the high temperature (90 °C), the composite hydrogels completely degrade into polymer solution within 72 h due to the ester-bond hydrolysis of PAM and hydrogen-bond disruption of PVA. At the same time, the released linear polymers enhance oil recovery by 3%, resulting in up to 57% oil recovery. The high plugging strength, flexible deformation, and controllable self-degradation of PAM@PVA hydrogel offer a novel approach to improving oil recovery processes in petroleum engineering.