Competing gravitational and viscous efects in 3D two-phase flow investigated with a table-top optical scanner

TL;DR

This study combines experiments and theory to analyze the transition from stable to unstable fingering in 3D two-phase flow within a synthetic porous medium, using a novel optical scanner for detailed observation.

Contribution

It introduces a new table-top 3D optical scanner and provides a theoretical framework for understanding the transition point based on viscous and gravitational effects.

Findings

Identification of a critical radius for flow transition

Observation of stable and unstable invasion zones

Validation of theoretical predictions with experimental data

Abstract

We present experiments and theory describing the transition from viscosity-stabilized flow to gravitationally unstable fingering for two-phase flow in a 3D synthetic porous medium. Observation is made possible by the use of our newly developed table-top 3D-scanner based on optical index matching and laser-induced fluorescence, which is described in detail. In the experiment, a more dense, more viscous fluid injected at a fixed flow-rate from a point source at the top of the flow cell displaces a less viscous, less dense fluid. We observe a stable invasion zone near the inlet, which increases in size with increasing flow rates, and presents initially a close to hemispherical shape. At later times, the invasion front transits to an unstable mode and a fingering flow regime. The transition occurs at a predicted critical radius, Rc, corresponding to the zero of the combined viscous and gravitational pressure gradient.