High-Density Weak Hydrophobe Polymer for Heavy Oil Recovery in Hypersaline Reservoirs: Synergistic Mobility Control and Wettability Reversal

The efficient recovery of heavy oil in hypersaline reservoirs (>100,000 mg·L–1 TDS) remains a critical challenge due to the rapid structural collapse of conventional hydrophobically associating polymers. Addressing this limitation, we propose a “High-Density Weak Hydrophobe” strategy. A novel amphiphilic terpolymer (AMDA) was synthesized via free-radical aqueous solution polymerization, featuring a remarkably high incorporation (14.3 mol %) of the short-chain, sterically bulky monomer diacetone acrylamide (DAAM). Unlike traditional polymers containing long-chain alkyl groups (e.g., C16-HMPAM) that undergo catastrophic “salting-out” and coiling at high salinity, AMDA constructs a dense yet reversible dynamic network, retaining over 81% of its viscosity at 90 °C in 100,000 mg·L–1 brine. This structural resilience enables the formation of ultrastable O/W emulsions, achieving a heavy oil viscosity reduction rate exceeding 95%. Core flooding experiments demonstrated an incremental oil recovery of 34.6% of the original oil in place (OOIP) at 65 °C. Furthermore, microfluidic visualization and zeta potential analysis revealed a synergistic EOR mechanism: beyond macroscopic mobility control, AMDA facilitates in situ emulsification and induces a wettability reversal from oil-wet to water-wet by establishing a robust electronegative hydration layer on the rock surface. This study validates the “High-Density Weak Hydrophobe” paradigm as a superior alternative to conventional strong-hydrophobe systems, offering a robust solution for enhanced oil recovery in harsh saline environments.