POROUS-MEDIA - A MODEL SYSTEM FOR THE PHYSICS OF DISORDER

We discuss several examples of applications of soft matter and statist ical physics to various problems related to porous and fractured media . The structure of porous media often displays multiple scale features which can be analysed by neutron diffraction or electron microscopy a nd can be approached by fractal models. Such characteristics are also observed on the surface of natural fractures.The relation between vari ous transport parameters such as permeability or conductivity introduc e characteristic microscopic length scales which can sometimes be inde pendently determined. In some cases, if the porous medium get clogged or if the number of flow channels or fractures is low enough so that t hreshold effects appear which can be analysed in terms of percolation models. Disorder physics approaches are particularly useful to analyse non miscible diphasic flows in some cases in which multiscale heterog eneities of the fluid mixture composition appear. This is for instance the case for very slow non wetting invasions and of the fast injectio n of a low viscosity fluid : these processes can be described respecti vely by the ''invasion percolation'' and the ''diffusion limited aggre gation'' models. Finally tracer dispersion provides an application of random walk models to disordered systems : examples of the response of this measurement in partly saturated and double porosity media are pr esented.