Microfluidic study and modeling of end-point permeability of multiphase flow*

At the endpoint of a multiphase flow in a porous medium, only a single phase is flowing and the other phases are stationary. The permeability of the medium to the flowing phase, the end-point permeability, sometimes is extremely low, despite that the flowing phase may still have an appreciable saturation. As an example, we note that flowing water or oil through porous media that have been previously infilled with polymer solution can be very difficult. In this study, we used microfluidics porous media micromodels to visualize the distribution of fluids at the endpoints of multiphase flows. These micromodels have close-to-real-rock pore dimensions and porosities. We found that the end-point relative permeability of water/oil after polymer flow was disproportionally low because these fluids must flow through highly tortuous pathways. A mathematical model was developed to describe the correlation between the pore-scale fluid distribution function and the end-point relative permeability; it can successfully predict the end-point relative permeability of all studied flows.