Experimental evaluation of fluid connectivity in two-phase flow in porous media

In this work, we provide a physically-consistent modeling approach for two-phase porous media flow, by including percolating interfacial area and saturation as state variables. For this purpose, we combine two continuum theories for two-phase flow which have been individually proven to be conditionally valid. This means the potential use of the connected-to-the-flow interfacial area as a state variable is tested utilizing time-resolved microfluidic experiments, for various flux boundary conditions. Moreover, we observe and study a linear relation between the percolating saturation and interfacial area, which is persistent for the tested boundary conditions. In our microfluidic experiments, we employ optical microscopy to perform cyclic immiscible displacement experiments. Our results show that a continuum model, where capillary pressure, saturation, and specific interfacial area of the clusters connected to the flow are considered, is closer to a universal description of two-phase flow than the common approaches, where the only state variable is saturation.