Résumé
Limestone rock dissolution induces geometrical parameters changes such as porosity, pore size distribution (connectivity), or tortuosity which may consequently modify transport properties (permeability, diffusion coefficient). Characterizing these changes is essential for modeling flow and CO2 transport during and after the CO2 injection. Indeed, these changes can affect the storage capacity and the injectivity of the formation. We report experimental results from CO2 rich-brine injection into limestone core samples of 9 mm diameter, 18 mm length. Experiments were performed at in situ conditions (T=100 degrees C and P=12 MPa) and with four different CO2 partial pressures (PCO2) varying from 0.034 to 3.4 MPa. X-ray microtomography (XMT) images are used to characterize, from pore scale to Darcy scale, the changes in the structural properties induced by the percolation of the CO2-rich brine. Coupling imaging techniques with sample scale measurements of the time-resolved permeability and chemical fluxes, allows determining the change in the chemical and physical parameters of the sample induced by the dissolution processes. The experiment results show localized dissolution features (wormhole formation) for the highest PCO2, whereas homogeneous dissolution is observed for the lower. The higher the CO2 concentration is the more ramifications at macro scale have growth into the sample and consequently the higher the permeability has increased. During low CO2 concentration injections, the dissolution processes may include transport of fine particles, which locally clog the porous space. This process is controlled by the differential dissolution rate of the calcite cement and calcite grains. This mechanism induces a decrease of permeability (while porosity increases) that may alter the CO2 injectivity.