A pore-scale simulation study of two-phase flow during water flooding in heterogeneous porous media

The two-phase displacement process occurring within the pores of a porous medium fundamentally represents the continuum-scale behavior of immiscible flow. Therefore, investigating pore-scale displacement patterns and flow morphologies provides deeper insight into the intrinsic mechanisms governing two-phase flow in geological formations. Unlike most previous studies, which mainly focused on single-factor effects, such as wettability or interfacial tension, this study develops a multi-parameter, coupled dynamic-capturing simulation framework that integrates the Navier–Stokes equations with the phase-field method. This framework systematically incorporates wettability, interfacial tension, pore-structure heterogeneity (disorder number λ), and surface roughness (root mean square) to elucidate their synergistic effects on immiscible displacement. Here, λ denotes a scalar heterogeneity index that sets the half-width of the uniform sphere-radius distribution in our model, i.e., r∈[(1−λ) r¯,(1+λ) r¯]; under this construction, the coefficient of variation satisfies COV = std(r)/r¯=λ/3, so larger λ monotonically increases geometric disorder [Blunt et al., “Detailed physics, predictive capabilities and macroscopic consequences for pore-network models of multiphase flow,” Adv. Water Resour. 25(8), 1069–1089 (2002) and R. Holtzman, “Effects of pore-scale disorder on fluid displacement in partially-wettable porous media,” Sci. Rep. 6(1), 36221 (2016)]. The simulations reveal the formation and evolution mechanisms of three residual oil forms: isolated oil droplets, oil columns, and clustered oil blobs, each arising from distinct structural configurations. This work provides a morphology-resolved, multi-parameter pore-scale analysis that integrates wettability, interfacial tension, quantified heterogeneity (λ), and surface roughness and highlights the dynamic fragmentation of clustered oil blobs. The findings provide a scientific basis for improving oil recovery in highly heterogeneous reservoirs.