Quantification of Microscopic Porous Networks By Image Analysis and Measurements of Permeability in the Soultz-Sous-Forêts Granite (Alsace, France)

Abstract

Natural or experimental fluid—rock interactions are often difficult to model theoretically because of the variability of the effective exchange surface area between the solid and the fluid. The freshest fades of the Soultz granite has been used previously for leaching experiments (Azaroual, Fouillac and Pauwels, 1993): a piece of core was crushed and leached with distilled water at 140°C, and the concentration of dissolved elements measured in the cell outflow. The computation of the distribution of the chemical species in the aqueous solution, and of their concentrations and activities with the EQ 3/6 software package (Wolery and Daveler, 1990), requires that the surface of exchange between the rock and the fluid is known. In order to match the results of the calculations with the experimental results, a 0.012 m2 g−1 exchange surface is required, whereas the exchange surface measured by BET (nitrogen adsorption) was 0.6 m2 g −1.