ИСТИНА

Understanding multiphase flow behavior at the pore scale is essential for optimizing enhanced oil recovery (EOR) strategies in complex reservoir environments. In this study, we present a pore-scale investigation of interfacial tension (IFT) effects on residual oil mobilization during surfactant flooding, using a microfluidic approach that mimics heterogeneous porous structures. Experiments were conducted with silicon–borosilicate microfluidic chips featuring regions of varying permeability to replicate realistic reservoir heterogeneity. A 0.3% surfactant solution was prepared in brines of four salinity levels - high, medium, low, and pure brine - corresponding to IFT values of 10- ³, 10- ², 10- ¹, and 10 mN/m, respectively. The displacement process included sequential injections of crude oil, pure brine, and surfactant solutions with increasing salinity, while pore-scale displacement dynamics were recorded using a high-resolution optical microscope. Image analysis enabled quantification of trapped oil, flow pathways, and emulsion formation under different IFT conditions. The results demonstrate a strong correlation between reduced IFT and enhanced displacement efficiency. Pure brine flooding primarily displaced oil from high-permeability zones, leaving significant residual oil in lowpermeability regions. In contrast, surfactant flooding promoted capillary number increase and enabled oil mobilization in both high- and lowpermeability areas. The lowest-IFT surfactant achieved the highest recovery 19 factor, confirming that interfacial tension reduction plays a dominant role in overcoming capillary trapping. This microfluidic visualization framework provides direct experimental evidence of surfactant efficiency at the pore scale and contributes to the understanding of flow behavior in heterogeneous media. The findings support the development of optimized surfactant formulations and injection strategies for improved oil recovery in complex reservoir systems.