The phenomenon of bioclogging in porous media is widely present in nature and engineering and is closely related to fields such as the environment, energy, and biomedical applications. In this work, we focus on the bioclogging process in porous media and investigate the effects of flow rate and pore size on the behavior of biofilm clusters and the evolution of permeability using a microfluidic chip-microscope-CMOS camera visualization experimental system. By integrating the microparticle image velocimetry technique, we achieved real-time dynamic observation of the flow field within porous media. Flow-visualization experimental results show that flow rate and pore size control the surface morphology and ultimate clogging efficiency of biofilms by influencing shear rates and nutrient exchange rates. It is shown that bioclogging in porous media presents two distinct clogging patterns, characterized by pattern Ⅰ with preferential flow paths and pattern Ⅱ without preferential flow paths. Pattern Ⅰ occurs under conditions of a smaller flow rate and larger pore size, where the fluid mainly flows concentrately in the preferential flow paths. The unevenness of the flow rate distribution is exacerbated over time, affecting the stability of clogging, and the permeability decline shows obvious intermittent fluctuations. Pattern Ⅱ occurs under conditions of a higher flow rate and smaller pore size, and the flow field distribution is relatively uniform with no obvious high-speed concentrated areas. In this pattern, the clogging effect is much more significant, with the permeability ratio being reduced by three orders of magnitude at the end of the experiments.

The capillary pressure curve is a fundamental constitutive relationship for simulating unsaturated flow and water-gas multiphase flow in porous media. As the wetting-phase saturation approaches the residual saturation, corner films and liquid bridges formed between solid grains become the dominant pathways governing fluid displacement processes. At present, the mechanisms by which corner films and liquid bridges influence capillary pressure curves remain insufficiently understood. In this study, a microfluidic visualization experimental platform was developed, and quasi-static drainage experiments were conducted in six sets of microfluidic models with different pore structures and surface roughness. The corner film-liquid bridge flow was directly observed, and its influence on capillary pressure curves was quantitatively evaluated. The results indicate that corner film-liquid bridge flow mainly occurs at low wetting-phase saturations and leads to a reduction in the residual wetting-phase saturation by 0.21-0.32. The occurrence of corner film-liquid bridge flow is closely related to the wettability of the porous medium; rough solid surfaces reduce the contact angle of the wetting phase, thereby facilitating the formation of corner films and liquid bridges. Moreover, the impact of corner film-liquid bridges is positively correlated with the number of liquid bridges, and their effect becomes more pronounced with decreasing porosity and heterogeneity of the porous medium.

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.