Capillary pressure-saturation and relative permeability curves are crucial for predicting multiphase fluid flow behavior in porous media, directly influencing the efficiency and reliability of subsurface engineering applications. At low saturations, the wetting-phase flow transitions from bulk displacement to being governed by corner and film flows along pore surfaces. Recent experiments and pore-scale simulations have shown that these microscale flow mechanisms preserve fluid connectivity and continue to influence macroscopic transport behavior, even after bulk flow pathways are no longer active. This work synthesizes current experimental and computational findings, highlighting how the formation and persistence of microscale flow networks made of corner and film flows influence capillary pressure and relative permeability curves, especially by enhancing wetting-phase connectivity at low wetting-phase saturations. Finally, key directions for future research are proposed to further enhance the understanding of how microscale film and corner flows influence macroscopic multiphase flow characteristics.

Multiphase flow in porous media is a common process in numerous engineering applications. While numerous studies have been conducted to investigate the impact of flow conditions, fluid properties, and wettability, the influence of flow geometry on the flow process remains poorly understood. Here, a theoretical model is proposed to directly forecast the displacement patterns across a wide range of porosity and disorder. This model is built upon the revelation that the overlap event stabilizes the invasion front, allowing us to predict displacement patterns by computing the probability of the overlap event. A value of 1 indicates a stable invasion process, resulting in compact displacement. Conversely, a value of 0 signifies an unstable invasion process, leading to capillary fingering. In the intermediate range between 0 and 1, a crossover zone is observed. The predicted phase diagram is evaluated using pore-network simulations and experiments in the literature, confirming that this model can reasonably predict displacement patterns under varying porosity and disorder. This contribution extends classical phase diagrams and holds practical significance for engineering applications.