Résumé
CO (sub 2) storage is a common practice in saline aquifers. This study concerns geological CO (sub 2) storage to be undertaken in a reservoir rock (limestone) which is a deep saline aquifer containing a NaCl- and sulfate-rich groundwater in equilibrium with calcite and gypsum. The reservoir rock is overlain by a very low permeability formation (marls), which acts as a caprock. During and after CO (sub 2) injection, the resulting CO (sub 2) -rich acid solution gave rise to the dissolution of calcite, albite, illite and clinochlore and the precipitation of secondary sulfate-rich minerals (gypsum and alunite), aluminosilicates (clay and zeolites) and aluminum and iron oxyhydroxides and sulfates. These reactions led to changes in porosity, pore structure and permeability of the caprock and also to the alteration of its CO (sub 2) seal capacity. To assess caprock reactivity, experiments using columns filled with crushed marly limestone, bituminous black shale and marl under different PTotal-pCO (sub 2) (atmospheric: 1-10-3.5 bar, subcritical: 10-10 bar and supercritical: 150-37 bar) and T (25 and 60 degrees C) conditions and using different input solution compositions (gypsum-undersaturated and gypsum-equilibrated) were conducted. 1D reactive transport modeling of the results enabled us (1) to interpret the overall processes that accounted for the considerable dissolution of calcite, minor dissolution of aluminosilicates and the precipitation of gypsum, kaolinite, zeolites and some aluminum and iron oxides and oxyhydroxides and sulfates and (2) to evaluate their implication for the hydrodynamic properties of the caprock. An increase in porosity over the column length, which occurred near the inlet, was calculated.