Formulation Optimization and Performance Characterization of Multi-Crosslinked CO2-Responsive Preformed Particle Gels

To address the issue of CO2 leakage induced by microcracks in cement sheaths during geological CO2 storage, this study developed a multi-crosslinked CO2-responsive preformed particle gel (MCCR-PPG) system. Using vinyl silica nanoparticles (VSNPs) as nano-crosslinkers and reinforcing agents, combined with CO2-responsive monomers, sodium alginate, organic crosslinkers, and ionic crosslinkers, an intelligent plugging material with a quadruple crosslinking network was constructed. The optimal formulation was determined through single-factor experiments: the molar ratio of DMAA, VIM, and NVP was 2:2:1; the dosages of crosslinker MBA and initiator APS were each 0.5% of the total monomer molar amount; the concentration of CaCl2 solution was 0.1 mol/L; and the VSNP content was 1 wt%. The results showed that the equilibrium swelling ratio of MCCR-PPGs in CO2 acidic solution reached 3200%, which was 4.27 times that in deionized water, demonstrating excellent CO2 responsiveness. Fracture plugging experiments further confirmed that the swollen gel formed a stable barrier within fractures, effectively preventing CO2 channeling with a breakthrough pressure differential of 2.008 MPa, indicating excellent plugging performance. This study provides a critical material solution for wellbore integrity in CCUS applications and holds significant engineering value for preventing CO2 leakage and ensuring storage safety.