CO₂-responsive terpolymer hydrogels with adjustable dynamic networks for fractured plugging in the reservoir

To address the limitations of conventional CO₂-responsive plugging materials (fixed network structure, slow response, and poor long-term stability) in fractured reservoirs, a novel terpolymer hydrogel poly(acrylamide-co-2-acrylamido-2-methylpropane sulfonic-co-acid-methylenebis(acrylamide)) hydrogel, denoted as P(AM-AMPS-MDA) was designed via solution copolymerization. The hydrogel features a hybrid network of covalent crosslinks (from MDA with tunable ethyleneamino chain length n = 1-3) and CO₂-induced ionic clusters, with precise reactant ratios (AM: AMPS: MDA = 90:16:4, K₂S₂O₈:Na₂SO₃=2:1) ensuring reproducibility. Comprehensive characterizations (FTIR, TGA/DSC, rheology, strain sweep) confirmed its superior performance: the optimized MDA₂ hydrogel (n = 2) exhibits rapid CO₂ response (< 10 min), balanced swelling ratio (~ 18), high storage modulus (1790 Pa), and excellent thixotropy (> 90% recovery in 30 s). It maintains structural integrity at 80 °C (T_d ≈ 617 °C) and retains > 85% mass over 10-year reservoir simulation. Core flooding tests and visual demonstrations validate its effective plugging (residual resistance coefficient > 20) and injectability. This design resolves key trade-offs in existing systems, providing a promising candidate for conformance control in CO₂-enhanced oil recovery and sequestration.