Ethoxy Chain Length Regulated Gemini Polymeric Surfactants for Enhanced Oil Recovery in High-Salinity Reservoirs

Under high-salinity conditions, Na⁺ primarily enhanced hydrophobic association and chain entanglement through electrostatic shielding, whereas Ca²⁺ induced intermolecular ion-bridging networks via multipoint coordination with carboxyl groups, resulting in distinct ion-specific regulation mechanisms. Benefiting from the optimal balance between hydrophobic association and EO chain interactions, AASD-O₁₀ maintained excellent interfacial activity in simulated formation water, reducing the oil–water interfacial tension to the order of 10^–3 mN/m and forming stable oil-in-water (O/W) emulsions with a heavy-oil viscosity reduction rate over 99%.

Microscopic displacement experiments demonstrated that all AASD polymeric surfactants outperformed conventional partially hydrolyzed polyacrylamide (HPAM), with AASD-O₁₀ achieving the highest oil recovery of 76.67%, which was 22.37 percentage points higher than HPAM. Molecular dynamics simulations further revealed the intrinsic relationships among EO chain length, ion-specific interactions, molecular association structures, and macroscopic oil displacement performance.

These findings provide new insights into the design of salt-tolerant polymeric surfactants and offer a promising strategy for enhanced heavy-oil recovery in high-salinity reservoirs.