Abstract:
Flow in porous media is essential to many aspects in our live, from irrigating plants or using oil recovered from the ground to the simple joys as percolating coffee. For a single phase, this flow is largely controlled by the hydraulic resistance. Introducing a second phase leads to a flow pattern governed by capillary forces. However, we show that interfacial drag forces between the phases can overcome capillary forces when exerted on a thin film. We use confocal microscopy to visualize these thin film formations between a trapped phase with surfactant and a flowing immiscible phase in three dimensional porous medium. We find that viscous drag forces on the thin film can destabilize capillary forces in drainage and imbibition, a process known as Haines jumps. Moreover, we show that viscous forces inhomogeneously deplete surfactant leading to variations in interfacial tension and localizing capillary destabilization. Our results suggest that even in steady state flow with no variations of pressure the trapped phase can be mobilized by the interplay of drag and capillary forces.