Drainage in two-dimensional porous media: from capillary fingering to viscous flow.

This paper reports some experimental results on two-phase flows in model two-dimensional porous media. Standard microfluidic techniques are used to fabricate networks of straight microchannels and to control the throat size distribution. We analyze both the invasion mechanism of the medium by a nonwetting fluid and the drainage after the percolation for capillary numbers lying between 10(-7) and 10(-2). We propose a crude model allowing a description of the observed capillary fingering that captures its scaling properties. This model is supported by numerical simulations based on a pore-network model. Numerical simulations and experiments agree quantitatively.