Going with the flow: colloidal dynamics at moving immiscible fluid interfaces

The presence of colloidal particles in geological media from diffusion of naturally occurring sediment and migration of microplastics can alter immiscible fluid displacement patterns that are central to enhanced oil recovery (EOR) and groundwater remediation. To understand the impact of deposited colloidal particles on immiscible flows, we visualize the interactions between colloidal deposits and moving immiscible fluid droplets in microchannels and develop a pore network model to predict the macro-scale implications of this process. As an immiscible fluid interface passes over particles, we observe that they strongly adsorb to it due to the influence of capillary forces exerted by the fluid interface as it impinges on particles. We see that the surface coverage of the interface increases with time as the fluid droplet traverses the channel, eventually reaching a finite “carrying capacity,” after which it must continually slough off excess particles. Two-dimensional simulations reveal striking deviations from immiscible fluid displacement via standard capillary fingering. Surprisingly, under certain deposition and erosion conditions, the immiscible fluid explores a larger pore space volume than what it can access through capillary fingering alone, establishing patterns that we term “erosion-enhanced fingering.”