Formation of Common Preferential Two-Phase Displacement Pathways in Porous Media

Including specific interfacial area and saturation of the percolating phase into two-phase porous media flow models, on the Darcy scale, enhances our ability to capture the physical properties of porous media flow more effectively. Using optical microscopy and microfluidic devices, we perform sequential drainage and imbibition experiments. The relevant processes, images, and boundary pressures are monitored, recorded, and logged at all times. For comparative purposes, two PDMS micromodels are used, one with an ortho-canonical, homogeneous, and the other with a periodic heterogeneous pore network, with similar macro- but different pore-scale properties. After processing the images, parameters like interfacial area belonging to percolating and non-percolating phases and the corresponding phase saturations are determined. Our experimental results show that the relation between specific interfacial area and saturation of the percolating invading phase is a linear relationship with interesting properties. Additionally, after a number of fluid displacement processes (drainage and imbibition), and for both pore networks, unique flow paths for both phases are formed. We speculate that this happens due to the establishment of an effective porous medium, meaning a hydro-dynamically active region within the pore space where the corresponding phase remains connected and flowing, where the capillary forces act as the guide for creating the “path of least resistance” in a highly viscous flow regime by keeping the non-percolating phases in place. As the results can be specific to our experiments, more work needs to be done toward the potential generalization of these findings, especially in 3D flow domains.