Oil-water displacements in rough microchannels

We investigate the effect of wall roughness upon the entrapment of oil (alkanes) by water flooding in a microchannel. We use fluorescence microscopy to track the in situ oil displacement process in these channels of controlled wall roughness. We find that the viscosity contrast between water and oil determines whether the alkane phase is partially retained in the microchannel. Oil recovery rates are found to be controlled by the wall roughness and the flow rate in the experiment. We also perform the displacement experiments in novel microfluidic 2D porous networks and show that a small variation in the pore-size distribution is also a representation of the solid medium's roughness. We observe that the trapped oil in the porous network follows the same trend as in the rough microchannels, i.e., viscosity contrast, flow speed, and roughness govern the quantity of the trapped oil. We propose a scaling law to quantify the trapped fluid volume based on our experimental observations, which accounts for both the flow rate and the characteristic roughness of the system.