Construction of the Clay Inhibition System for Water-Sensitive Reservoirs and Mechanism Study on CO₂-Assisted Synergistic Oil Recovery

Aiming at the problems of high clay mineral content in strong water-sensitive reservoirs and easy hydration expansion caused by foreign fluids, a clay inhibitor (silyl quaternary ammonium salt DSC) was prepared using 2-(dimethylamino)-ethyl methacrylate and (3-chloropropyl)-trimethoxysilane as raw materials. This is the first report on the synergistic application of silyl quaternary ammonium salt (DSC) and CO₂ for enhanced oil recovery in strongly water-sensitive reservoirs, realizing the dual effects of clay stabilization and CO₂ seepage enhancement. It is demonstrated that the synergy of DSC/CO₂ increases the oil recovery rate by 47.29% compared to traditional water flooding, with a 0.35 PV delay in gas channeling. The DSC system, composed of DSC, ethylene glycol, inorganic salt, and nonionic surfactant, stabilizes pore structures through synergistic charge neutralization, hydrogen bond inhibition, and electric double-layer compression, with an antiswelling rate of 93.92% and dissolution rate of 5.32%. The study on the synergistic effect of the DSC system and CO₂ found that the CO₂ diffusion coefficient in DSC-saturated cores increased to 9.226 × 10^-9 m²/s (16 times higher than that in formation water-saturated cores), the initiation pressure gradient was reduced by 2 orders of magnitude compared with simulated water flooding, and the antiswelling rate decreased by only 13.72% after multiple rounds of flushing in an acidic environment. It was confirmed that DSC reconstructed the pore surface energy through silyl bonding, significantly improving the CO₂ seepage capacity. Nuclear magnetic resonance (NMR) proved from a microscopic perspective that the synergy of DSC and CO₂ increased the recovery rate of the remaining oil in small pores by 25.08%. Macroscopic oil displacement experiments further showed that the total recovery rate of DSC system flooding + gas-liquid alternating flooding reached 62.85%. The proposed technical model of "dual-effect stable flow-synergistic oil recovery-delayed gas channeling" provides a solution with both technical feasibility and economic rationality for the development of low-permeability water-sensitive reservoirs and CO₂ geological storage. Future research will focus on formula optimization and adaptability studies for reservoirs with different clay compositions.