Tuning capillary flow in porous media with hierarchical structures

TL;DR

This paper investigates how hierarchical pore structures can be engineered to suppress capillary fingering during fluid displacement in porous media, improving efficiency in applications like oil recovery and CO2 storage.

Contribution

It introduces a pore geometry adjustment method to control displacement patterns, demonstrating the transition from fingering to compact flow through simulations and analysis.

Findings

Higher porosity in second-order structures promotes compact displacement.

Hierarchical structures can suppress fingering across various wettability conditions.

Insights enable better design of microfluidic devices and porous media for enhanced fluid displacement.

Abstract

Immiscible fluid-fluid displacement in porous media is of great importance in many engineering applications, such as enhanced oil recovery, agricultural irrigation, and geologic CO2 storage. Fingering phenomena, induced by the interface instability, are commonly encountered during displacement processes and somehow detrimental since such hydrodynamic instabilities can significantly reduce displacement efficiency. In this study, we report a possible adjustment in pore geometry which aims to suppress the capillary fingering in porous media with hierarchical structures. Through pore-scale simulations and theoretical analysis, we demonstrate and quantify combined effects of wettability and hierarchical geometry on displacement patterns, showing a transition from fingering to compact mode. Our results suggest that with a higher porosity of the 2nd-order porous structure, the displacement can keep compact across a wider range of wettability conditions. Combined with our previous work on viscous fingering in such media, we can provide a complete insight into the fluid-fluid displacement control in hierarchical porous media, across a wide range of flow conditions from capillary- to viscous-dominated modes. The conclusions of this work can benefit the design of microfluidic devices, as well as tailoring porous media for better fluid displacement efficiency at the field scale.