Fluid breakup during simultaneous two-phase flow through a three-dimensional porous medium

TL;DR

This study visualizes how two fluids flow through a 3D porous medium, revealing a transition from connected pathways to breakup into ganglia driven by flow rates and fluid properties.

Contribution

It provides the first direct visualization of simultaneous two-phase flow in 3D porous media and characterizes the flow transition using a state diagram based on capillary numbers.

Findings

Low flow rates maintain connected flow pathways.

High flow rates cause non-wetting fluid breakup into ganglia.

Flow transition depends on capillary numbers of both fluids.

Abstract

We use confocal microscopy to directly visualize the simultaneous flow of both a wetting and a non-wetting fluid through a model three-dimensional (3D) porous medium. We find that, for small flow rates, both fluids flow through unchanging, distinct, connected 3D pathways; in stark contrast, at sufficiently large flow rates, the non-wetting fluid is broken up into discrete ganglia. By performing experiments over a range of flow rates, using fluids of different viscosities, and with porous media having different geometries, we show that this transition can be characterized by a state diagram that depends on the capillary numbers of both fluids, suggesting that it is controlled by the competition between the viscous forces exerted on the flowing oil and the capillary forces at the pore scale. Our results thus help elucidate the diverse range of behaviors that arise in two-phase flow through a 3D porous medium.