Impact of wetting films on the stability of two-phase flow in porous media: A pore-doublet perspective

Abstract

Two-phase flow stability in porous media depends on a complex interplay between surface tension effects and viscous forces. We investigate the role of wetting films on the stability of two-phase flow during drainage. Such films are ubiquitous in porous media and are deposited at the solid walls and corners after the passage of the meniscus. We derive a novel dynamic pore-doublet model with identical channels that includes the effects of lubricating films. Direct comparisons with microfluidic experiments highlight that neglecting wetting films in pore-doublets analysis leads to significant prediction errors. We demonstrate that pore-doublet models with wetting films reproduce stability phase diagrams similar to the so-called Lenormand diagrams. At high viscosity ratios, our model predicts phase transition between stable, viscous, and capillary fingering regimes that agree very well with Lenormand phase diagrams obtained using complex porous structures. Our study demonstrates that using simple systems, such as pore doublets with lubricating films, allows us to capture the non-linear response of two-phase flow stability similar to those observed in complex pore networks.