Oil Displacement Performance and Mechanism of a Surfactant-Synergistically Enhanced Inclusion System in High-Temperature and High-Salinity Reservoirs

To address the limitations of conventional polymer flooding systems regarding temperature and salt tolerance, a surfactant-synergistically enhanced inclusion system was constructed using zwitterionic surfactants and host–guest inclusion systems, which exhibit excellent temperature and salt resistance, shear recovery properties, and ultralow interfacial tension (IFT, 1.0 × 10–3 mN/m) reduction capabilities. Under simulated conditions representative of Shengli Oilfield Class-III reservoirs, systematic core flooding experiments employing both homogeneous and heterogeneous physical core models were conducted to evaluate the system's oil displacement efficacy and profile control performance. Mechanistic investigations encompassing adsorption behavior, wettability alteration capabilities, crude oil emulsification performance, and real-time pore-scale fluid distribution dynamics revealed its enhanced oil recovery (EOR) mechanisms. Results indicate optimal compatibility with homogeneous cores exhibiting permeabilities of approximately 200 × 10–3 μm2. With the increase of injection volume, the increment in oil recovery efficiency increases. When the injection volume is 0.5 PV, the final oil recovery efficiency can reach 60.13%, with an increment of 24.75%. In heterogeneous formations, the system exhibited excellent fluid diversion capability by increasing flow resistance in high-permeability zones and redirecting fluids to low-permeability regions, yielding a 23.85% incremental recovery. The oil displacement mechanism is mainly as follows: Its excellent viscoelastic properties can effectively expand the sweep efficiency; appropriate adsorption on the rock surface causes wettability alteration, making crude oil easy to peel off; finally, it improves oil washing efficiency by reducing IFT and emulsifying, aggregating, carrying, and stripping crude oil, thereby effectively enhancing oil recovery. These mechanistic insights establish the theoretical foundation for field applications in high-temperature and high-salinity reservoirs.