Controlling fingering instabilities

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The process and dynamics of a viscous fluid displaced by another are omnipresent, affecting a myriad of both natural phenomena and technological applications involving fluid--fluid displacement. In particular, when a less viscous fluid displaces another immiscible one (such as water pushing oil), a hydrodynamic instability triggered by a viscosity contrast can occur with a wavy interface in a porous medium or narrow passage. This so--called viscous fingering instability produces a finger--shaped propagation front with a partial sweep of the displaced fluid (e.g., oil), thereby detrimentally hampering a variety of technologies. For example, the viscous fingering instability is notoriously a critical limiting factor for enhanced oil recovery, groundwater technologies, and printing processes, to name a few. The control of viscous fingering instability is, however, difficult and challenging because the fluids are often pre--selected and, hence, their viscosity contrast is a given factor that predominately determines the flow instabilities. This Discovery program tackles this challenge and aims at both innovative control and critical understanding of the viscous fingering instability at both micro- and macro--scales. We will conduct both microfluidic and large--scale experiments with a novel approach to elucidate the dynamics and mechanism of the interfacial profiles between the fluids. To this end, three comprehensive projects are proposed to carry out state--of--the--art experiments using (i) complex fluids, (ii) microfluidics, and (iii) electrical means. These projects also aim to fill the crucial gaps in the literature regarding how to control complex viscous fingering in a tapered cell macroscopically, in heterogeneous pore--structures, and under external electrical means, respectively. With these sets of novel experimental configurations, several HQPs (highly qualified personnel) will carry out high--resolution measurements of the interfacial profile and recovery rate for a less viscous fluid displacing a more viscous, complex fluid. The quantitative results obtained include time--varying interfacial profiles and recovery rates under different flow rates and, hence, the important phase diagram of stable vs. unstable viscous fingering for complex fluids, which are rarely explored comparing to simple, Newtonian fluids. We will elucidate the mechanisms and know--how on how to control the viscous fingering instability for complex fluids in porous media with experiments. We will apply new insights gained in this program to help to improve the disadvantageous partial sweep and recovery of complex viscous fluids. The expected results will benefit various applications for the oil and gas industry, carbon capture and storage in saline aquifers, chromatography technologies, membrane applications, and groundwater technologies.