Electrokinetic Control of Viscous Fingering in a Perfect Dielectric Fluid

Abstract

Viscous fingering (VF) is a well-known interfacial instability occurring when a viscous fluid in a porous medium is displaced by a lower viscosity fluid. In this work, we show that electrokinetic control of the instability is possible, even in the case of a perfect dielectric viscous defending fluid. Using Hele-Shaw cell experiments in which a nonconducting viscous mineral oil is displaced by a conducting less viscous brine solution, we observe that we are able to effectively control the stability of the interface. We evaluate the interfacial stability at different field strengths, both positive and negative with respect to the pressure-driven flow and find that an electric field in the same direction as the pressure-driven flow significantly stabilizes the interface. In contrast, an electric field opposing the pressure-driven flow further destabilizes the displacement. We attribute this to the interplay between the different $\ensuremath{\zeta}$ potentials (fluid-fluid and fluid-wall) and preferential oil wettability of the system, resulting in the formation of an oil-film layer throughout the displacement. The nonconducting mineral oil in our system acts then as a dead-end pore for the brine, which under the influence of an electric field develops an electro-omostic flow velocity. We qualitatively and quantitatively show that for all positive electric field strengths VF is reduced, while for negative electric fields VF is increased and that the electric field strength has limited influence on the degree of (de)stabilization. The results from this work are of particular relevance in applications where VF occurs in a system containing one nonconducting fluid, which are common in many applications such as enhanced oil recovery.