Résumé
Reactive transport processes can be observed in different contexts such as acidic main drainage, CO (sub 2) geological storage, geothermal production, contaminant transport for examples. In some of these cases, the rock will react with the percolation fluid and dissolution/precipitation processes will appear. One of the most sensitive rock is carbonate rock. Carbonate rocks dissolution induces geometrical parameters changes such as porosity, pore size distribution, or tortuosity which may consequently modify transport properties (permeability, diffusion coefficient). Characterizing these changes is essential for modelling flow and reaction rates for CO (sub 2) geological storage, geothermal production, contaminants transport,... Very few published studies evaluate the transport properties changes (porosity, permeability, pore size distribution, diffusion coefficient) due to fluid-rock interactions (dissolution and/or precipitation). Here we report experimental results from the injection of acidic fluids (some of them equilibrated with gypsum) into limestone and dolostone core samples of 25.4 mm diameter and around 25 mm length. We studied two different carbonate rocks: one composed of 73% of calcite and 27% of quartz, and the second one of 100% of dolomite. Experiments were realized at room temperature. Before and after each acidic rock attack, we measure the sample porosity, the diffusion coefficient and the pore size distribution. We also imaged the 3D pore network by X-ray microtomography to evaluate the same parameters. During percolation experiments, the permeability changes are recorded and chemical samples taken to evaluate calcite dissolution and gypsum precipitation. Several dissolution/precipitation-characterization cycles are performed on each sample in order to study the evolution and relation of the different parameters. These experiments show different dissolution regimes depending of the fluid acidity, the mineralogy and also the initial local heterogeneities, and pore size distribution.