Forced Imbibition in Stratified Porous Media

TL;DR

This study visualizes and analyzes how fluid imbibition behaves in stratified porous media, revealing a capillary number-dependent invasion pattern and providing a predictive stability model.

Contribution

It introduces a direct visualization of forced imbibition in 3D stratified media and develops a linear stability analysis to predict invasion behavior.

Findings

Wetting fluid prefers fine strata at low Ca

Above a threshold Ca, invasion shifts to coarse strata

The threshold depends on geometry, fluid properties, and residual films

Abstract

Imbibition plays a central role in diverse energy, environmental, and industrial processes. In many cases, the medium has multiple parallel strata of different permeabilities; however, how this stratification impacts imbibition is poorly understood. We address this gap in knowledge by directly visualizing forced imbibition in three-dimensional (3D) porous media with two parallel strata. We find that imbibition is spatially heterogeneous: for small capillary number Ca, the wetting fluid preferentially invades the fine stratum, while for Ca above a threshold value, the fluid instead preferentially invades the coarse stratum. This threshold value depends on the medium geometry, the fluid properties, and the presence of residual wetting films in the pore space. These findings are well described by a linear stability analysis that incorporates crossflow between the strata. Thus, our work provides quantitative guidelines for predicting and controlling flow in stratified porous media.