Numerical modeling of fluid-rock chemical interactions at the supercritical CO2-liquid interface during CO2 injection into a carbonate reservoir, the Dogger aquifer (Paris Basin, France)

A project of geological CO2 storage in the deep Dogger aquifer in the Paris Basin (France) is under development. Before effective containment can be assured, investigations need to be carried out on reservoir behavior when subjected to physical, chemical and mechanical perturbations induced by CO2 injections. The aim of this study is to present the numerical results of two CO2 injection scenarios, firstly with CO2-saturated water and secondly with pure supercritical CO2. The simulation results confirm the high reactivity of CO2-saturated water, which can dramatically damage the reservoir structure. On the other hand, supercritical CO2 injection appears to be weakly reactive, with a limited modification of well injectivity. Supercritical CO2 reacts differently to CO2-saturated solution: firstly, it dissolves into aqueous solution and it increases both water acidity and mineral dissolution potential, favoring augmented porosity. Following this step, numerical simulations demonstrate that hydraulic processes induced by supercritical CO2 injection are accompanied by a desiccation phenomenon of the porous medium. Irreducible water, entrapped in pores, sustains the increase in CO2 pressure. When the pressure is sufficiently high and under a continuous dry (without water vapor) CO2 flux, an evaporation process starts leading to the precipitation of salts and possibly other secondary minerals. Although there has been little focus on this desiccation process in the literature until now, it nevertheless must constitute an important risk of both a modification in porosity and well injectivity. (C) 2007 Elsevier Ltd. All rights reserved.