Impact of CO2-induced Geochemical Reactions on the Mechanical Integrity of Carbonate Rocks

Abstract

In a CO2 storage site, carbonate rocks might be good reservoir rocks or good seals depending on their porosity and permeability. However, these properties may change in time due to deformation processes related to CO2 injections and/or withdraws. In this pilot study, we investigate at the laboratory scale the influence of CO2-induced geochemical reactions on the mechanical integrity of carbonate rocks. To achieve this target, we have performed an experimental HP-HT test on brine saturated oolitic limestone samples that were exposed to 230 bar CO2 pressure and 37.5oC reaction temperature (supercritical conditions) for a period of 2 weeks. Although changes in fluid chemistry have been identified via ICP-OES analysis, we have observed no particular differences in terms of ooids and cement deformation and/or calcite dissolution when comparing ESEM images of pre- and post-treatment samples. We are currently performing more experiments under different conditions (particularly longer exposure and higher brine-rock ratios that can be linked to higher dissolution of calcite) in order to better understand the dominant CO2 sequestration mechanisms in oolitic limestone-containing reservoirs.