Suppressing viscous fingering in structured porous media

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 115; no. 19; pp. 4833 - 4838
• Main Authors: Rabbani, Harris Sajjad, Or, Dani, Liu, Ying, Lai, Ching-Yao, Lu, Nancy B., Datta, Sujit S., Stone, Howard A., Shokri, Nima
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 08.05.2018
• Subjects: Columns (structural); Computational fluid dynamics; Computer simulation; Design engineering; Displacement; Fluid dynamics; Interface stability; Mathematical models; Miscibility; Morphology; Percolation theory; Physical characteristics; Physical Sciences; Pore size; Porosity; Porous materials; Porous media; Simulation; Viscosity; suppressed viscous fingering; direct numerical simulation; analytical model; structured porous media; microfluidics
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1800729115

Finger-like protrusions that form along fluid–fluid displacement fronts in porous media are often excited by hydrodynamic instability when low-viscosity fluids displace high-viscosity resident fluids. Such interfacial instabilities are undesirable in many natural and engineered displacement processes. We report a phenomenon whereby gradual and monotonic variation of pore sizes along the front path suppresses viscous fingering during immiscible displacement, that seemingly contradicts conventional expectation of enhanced instability with pore size variability. Experiments and porescale numerical simulations were combined with an analytical model for the characteristics of displacement front morphology as a function of the pore size gradient. Our results suggest that the gradual reduction of pore sizes act to restrain viscous fingering for a predictable range of flow conditions (as anticipated by gradient percolation theory). The study provides insights into ways for suppressing unwanted interfacial instabilities in porous media, and provides design principles for new engineered porous media such as exchange columns, fabric, paper, and membranes with respect to their desired immiscible displacement behavior.