From Capillary Fingering to Viscous Flow in Two-Dimensional Porous Media: Role of the Wetting Properties

Microfluidics device are used to study the drainage of a wetting fluid by a non-wetting one in porous media. Both the geometry and the wetting properties are accurately controlled and allow to obtain quantitative measurements of the features of the capillary fingering occuring during the invasion as a function of the imposed flow rate. In partial wetting systems, a quantitative agreement is found between the experimental mean velocities, a simple model based on scaling arguments, and some simulations based on a pore network model. In total wetting systems, the correlation length is higher than predicted in the capillary regime. Furthermore, a very different behavior is observed after the percolation, the invasion process do not stop in total wetting systems whereas the structure of the flow is frozen in partial wetting ones.