# Controlling capillary fingering using pore size gradients in disordered media

## TL;DR

This study demonstrates that introducing pore size gradients in disordered porous media can effectively control capillary fingering, with experimental and computational evidence showing suppression of fingering at sufficient gradient magnitudes.

## Contribution

The paper reveals how pore size gradients influence capillary fingering, providing a new method to control flow in porous media through gradient manipulation.

## Key findings

- Pore size gradients can suppress capillary fingering.
- Flow behavior depends on gradient direction and magnitude.
- A non-dimensional parameter describes flow regimes.

## Abstract

Capillary fingering is a displacement process that can occur when a non-wetting fluid displaces a wetting fluid from a homogeneous disordered porous medium. Here, we investigate how this process is influenced by a pore size gradient. Using microfluidic experiments and computational pore-network models, we show that the non-wetting fluid displacement behavior depends sensitively on the direction and the magnitude of the gradient. The fluid displacement depends on the competition between a pore size gradient and pore-scale disorder; indeed, a sufficiently large gradient can completely suppress capillary fingering. By analyzing capillary forces at the pore scale, we identify a non-dimensional parameter that describes the physics underlying these diverse flow behaviors. Our results thus expand the understanding of flow in complex porous media, and suggest a new way to control flow behavior via the introduction of pore size gradients.