Ganglion startup in porous media

Abstract

In porous media, dispersed fluid ganglia (bubbles, droplets) largely shape flow, transport, and chemical reactions. Static trapping and steady-state mobilization of ganglia have been extensively studied. However, the transition from trapping to mobilization (ganglia startup) has received less attention. Here we investigate ganglia startup in a 2-D uniform porous medium subject to an external field. When the external field quasi-statically increases from zero, a ganglion first irreversibly and discretely reformulates without mobilization; when the external field reaches a criterion, the ganglion starts to mobilize by sequential non-equilibrium jumps. Surprisingly, startup significantly reduces ganglia’s capillary hysteresis: although a static ganglion with a fixed volume has multiple metastable morphologies, it normalizes into one “kick-off” state before startup, at which state the ganglion’s morphological and thermodynamical properties fall into very narrow range regardless of volume. It allows analytical resolution of the startup criterion and may largely simplify multiphase fluids modeling in porous media.