| Popis: |
Understanding the fate of CO2 disposed in aquifers or depleted hydrocarbon fields is partly based on the use of reaction-transport models, able to predict the possible interaction between acidified waters and the minerals. The results delivered by such models depend on many parameters and hypotheses, of which some are still poorly constrained. A key issue is how to transpose kinetics of a mineral reaction to a representative rock system, from data acquired in laboratory experiments involving controlled mineral powders under high water-tomineral ratio. The paper focuses on the simulation of plug-flow experiments designed to improve the upscaling of kinetic rates. The experiments were performed on a natural limestone made of pure calcite (Noiriel et al., this issue), in conditions of temperature, pressure, pCO2 and water composition for which a kinetic rate of dissolution is available for calcite (Plummer et al., 1978, the so-called PWP model). A reactiontransport code is used to simulate the experiment and then to investigate the transposition of the kinetic rate from the mineral to the rock material. However, the comparison between experimental and modelling results cannot help to understand what is the main control on the dissolution rate of limestone in the conditions studied, either the surface reaction or a transport mechanism in the water phase. In the first case, a value of the reactive surface area must be adjusted. In the second case, the fitting parameter is the average thickness of a diffusive layer, which depends on pH. |
