Abstract: In response to the issue of preformed particle gel (PPG) degradation and dehydration caused by the acidic environment formed during CO₂ flooding,a CO₂-responsive preformed particle gel (CR-PPG) with a triple crosslinked network was prepared using N,N-dimethylacrylamide (DMAA),vinylimidazole (VIZ),and N-vinylpyrrolidone (NVP) as the main raw materials,along with the organic crosslinking agent N,N′-methylenebisacrylamide (MBA) and the nano-crosslinking agent vinyl silica nanoparticles (VSNPs),through aqueous solution polymerization.System optimization,CO₂ responsiveness testing,conductivity testing,rheological testing,and core displacement experiments were conducted.The study shows that the optimal ratio of the monomers DMAA,VIZ,and NVP was found to be 2∶2∶1.The CR-PPG exhibited excellent CO₂ responsiveness and mechanical strength,demonstrating efficient plugging and profile control capabilities during CO₂ flooding.The CO₂ responsiveness mechanism of CR-PPG is attributed to the protonation effect of the tertiary amine groups in its structure under CO₂ acidic conditions.This study provides an important basis for plugging and profile control operations during CO₂ flooding.

Key words: CO₂ flooding, non-homogeneous reservoir, triple crosslinking, preformed particle gel, nano-crosslinking agent