EXPERIMENTAL-STUDY OF TRACER DISPERSION IN FLOW THROUGH TWO-DIMENSIONAL NETWORKS OF ETCHED CAPILLARIES

We analyze experimentally the relation between the length scales characterizing the heterogeneity of a porous medium and the tracer dispersion coefficient D at a velocity U. Experiments are performed on two-dimensional lattices of millimetric channels. For a partly connected network with a percolation geometry we find D is close to the percolation correlation length and much larger than the individual size. This variation is in agreement with the Staffman model for mechanical dispersion. Experimental curves are non-Gaussian and no U2 contribution to D associated with zero-velocity zones could be detected because of the long exchange times with them.