Two phase flows in porous media: New dynamics for an old problem

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