Impact of Wettability on Fluid-Fluid Displacement in Porous Media: A Pore-Scale Model

Abstract:

The displacement of a fluid by another in porous media is affected by the wetting properties of the medium. While the wettability can vary significantly, its impact is poorly understood. Here, we study the effect of wettability on the invasion patterns via a pore-scale model. We simulate the invasion of an inviscid fluid into a medium saturated with a viscous fluid, for various contact angles and injection rates. We show that increasing the contact angle (making the invading fluid more wetting) stabilizes the invasion front. In particular, at low injection rates, the invasion pattern becomes compact despite of the large, unfavorable viscosity ratio. These results compare favorably with experiments, in which air is injected in a Hele-Shaw cell filled with chemically-treated glass beads and saturated with water/glycerol. Our simulations suggest that the stabilization of the invasion front is due to the increasing dominance of cooperative, non-local invasion mechanisms. For nonwetting invasion (small contact angles, or drainage), the dominant mechanism is Haines jumps, which are controlled by the local pressure drop across individual menisci, whereas for wetting invasion (large contact angles, or imbibition) the stability of individual menisci depends on adjacent parts of the interface.