The role of wetting on the flow of two immiscible fluids in porous media

TL;DR

This study uses advanced numerical simulations to explore how wettability and capillary number influence the interface dynamics between two immiscible fluids in porous media, revealing distinct flow regimes and new measurement techniques.

Contribution

It introduces a hybrid phase field-immersed boundary method to model contact line dynamics without empirical models and maps flow regimes in the capillary number-contact angle plane.

Findings

Capillary fingering occurs at low Ca and hydrophobic surfaces.

Stable penetration dominates on hydrophilic surfaces.

Pressure for invasion decreases with Ca and increases with contact angle.

Abstract

We study the role of the capillary number, $Ca$ and of the surface wettability on the dynamics of the interface between an invading and a defending phase in a porous medium by means of numerical simulations. We employ a hybrid phase field-immersed boundary approach to successfully model the contact line dynamics over the solid objects. Using a phase-field method which naturally incorporates dynamic wetting we eliminate the need for empirical contact line models to address contact line singularity. We map the two dominant modes governing the motion of the interface, namely, capillary fingering, and stable penetration, in the ($Ca$-$\theta$) plane, with $\theta$ the static contact angle prescribed at the solid pores. Capillary fingering dominates at lower values of $Ca$ and pores hydrophobic to the invading phase, while a stable penetration is observed on hydrophillic surfaces. We present new measurements and analyses, including curvature probability density functions (pdf) and average curvature. We also show that the pressure needed for the invading phase to advance at constant flow rate decreases with the capillary number, and increases with the contact angle at the capillary numbers considered. The latter is due to a significant increase of the length of the interface in the case of capillary fingering. Finally, we show that it is possible to identify the different interfacial modes by measuring the penetration length and velocity during the medium filling.