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

TLDR: In this paper, confocal microscopy was used to visualize the simultaneous flow of both a wetting and a nonwetting fluid through a model 3D porous medium, and it was shown that for small flow rates, both fluids flow through unchanging, distinct, connected 3D pathways; in contrast, at sufficiently large flow rates the non-wetting liquid is broken up into discrete ganglia.

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.

Figures

FIG. 1: (a) Schematic showing porous medium and imaging geometry. The oil flows at a rate Qnw through a circular tube inserted coaxially in a larger square quartz capillary, whereas the wetting fluid flows at a rate Qw via two additional opposing circular tubes (not shown for clarity) positioned at the inlet of the square capillary, through the interstitial space between the oil circular

FIG. 3: State diagram of the transition from fully connected to broken up flow for simultaneous two-phase flow through a 3D porous medium as a function of Caw and Canw. Open symbols represent flow of the non-wetting fluid through a connected 3D pathway, grey symbols represent intermittent breakup of this pathway, and black symbols represent continual breakup of the oil into discrete ganglia, which are advected through the pore space. Each symbol shape represents a

FIG. 2: Oil breaks up for sufficiently large flow rates. Images show multiple frames, taken at different times, of a single optical slice, with the beads and the pore space subtracted; thus, the