Interplay of Interfacial Tension Reduction and Wettability Alteration During Surfactant Flooding: A Pore‐Scale Lattice Boltzmann Investigation

Abstract Surfactant flooding is a promising strategy for subsurface fluid recovery and environmental remediation, wherein interfacial tension (IFT) reduction and wettability alteration are the two principal mechanisms governing residual phase mobilization. Yet attributing their interplay and relative contributions remains challenging because the two processes are intrinsically coupled. To address this, we develop a pore‐scale lattice Boltzmann model that concurrently incorporates surfactant transport, IFT reduction, adsorption‐induced wettability reversal, and tunable solubility contrast, providing a versatile platform to explore displacement physics. We then investigate the individual and combined effects of IFT reduction and wettability alteration under varying capillary numbers, viscosity ratios, and pore‐scale disorder. We find that both mechanisms improve displacement efficiency by stabilizing the displacement front: IFT reduction raises the local capillary number to suppress selective invasion, while wettability reversal promotes cooperative pore filling. Their synergy leads to more compact invasion patterns and reduced residual saturation. Morphologically, IFT reduction results in dispersed oil ganglia, whereas wettability reversal favors network‐like trapping. We observe a capillary number‐dependent shift in the dominant mechanism, controlled by surfactant diffusivity and adsorption loss: IFT reduction dominates at low capillary numbers, whereas wettability alteration becomes more influential at high capillary numbers and then levels off. Wettability reversal also shows superior robustness under high viscosity contrast and structure disorder by mitigating bypassing flow. These findings offer new mechanistic insight into the coupled physics of surfactant flooding and provide guidance for the rational design of injection strategies and chemical formulations in enhanced oil recovery and subsurface remediation.