Visualization by optical fluorescence of two-phase flow in a three-dimensional porous medium

TL;DR

This paper presents a novel optical fluorescence method to visualize and analyze three-dimensional two-phase flow in porous media, revealing flow patterns and the influence of various forces.

Contribution

It introduces a refractive index matching and laser scanning technique to visualize 3D flow in opaque porous media, advancing understanding of complex two-phase flow behaviors.

Findings

Observation of a compact invading fluid region with finger-like protrusions.

Increased flow rate enhances the dominance of the compact region.

Flow patterns are influenced by gravitational, viscous, and capillary forces.

Abstract

Slow flow of a single fluid through a porous medium is well understood on a macroscopic level through Darcy's law, a linear relation between flow rate and a combination of pressure differences, viscosity, and gravitational forces. Two-phase flow is complicated by the interface separating the fluids, but understanding of two-dimensional, two-phase flow has been obtained from experiments using transparent cells. In most three-dimensional media, however, visual observation is difficult. Here, we present preliminary results of experiments on a model medium consisting of randomly packed glass spheres, in which one fluorescent liquid invades another. By refractive index matching and scanning with a sheet-shaped laser beam, we obtain slices of the flow patterns, which we combine into three-dimensional pictures. We observe a compact region of invading fluid, surrounded by finger-like protrusions. The compact region becomes more dominant with increasing invader flow rate. The patterns are theoretically analyzed in terms of the interplay between gravitational, viscous, and capillary forces.