Synergistic Mechanism and Performance Optimization of High-Temperature Clay Stabilizer Compound System for Thermal Recovery of Heavy Oil in Bohai Oilfield

To address the issues of reservoir permeability decline and steam injection pressure increase caused by clay swelling during heavy oil thermal recovery in Bohai Oilfield, this study developed a high-temperature synergistic anti-swelling system, CYF-3 (40% CETA +20% PDADMAC +40% water), through the compounding of cationic polymer (PDADMAC) and quaternary ammonium salt (CETA). Experimental results demonstrated that CYF-3 achieved an anti-swelling rate of 95.2% and a water-washing resistance rate of 99.0% after 24 h of aging at 300 °C, with excellent compatibility with formation water (no precipitation observed over 120 h) and a solid content of 48.5%. In core flooding experiments, a 4% CYF-3 preflush solution improved permeability retention rate to 87.9% and reduced steam injection pressure differential to 0.068 MPa, significantly outperforming conventional systems. Microstructural characterization combined with molecular dynamics simulations revealed its mechanism: neutralizing negative charges on clay surfaces (54.5% increase in zeta potential), compressing interlayer basal spacing (18.8% reduction), and forming a hydrogen bond network (average hydrogen bond count ≥5), effectively inhibiting clay swelling and migration. Notably, the electrostatic adsorption binding energy between CETA and clay reached −285 kJ/mol, while PDADMAC enhanced adsorption stability through hydrogen bonding. Their synergy established a dense protective barrier. This system exhibits high-temperature resistance, long-term anti-swelling efficacy, and low reservoir damage, providing an efficient solution for shallow heavy oil thermal recovery in Bohai Oilfield.