Effects of the presence of CO2 at the well/caprock interface: Crystallization damage

In the context of CO2 geological storage, it is important to assess the safety and efficiency of the storage operation and thus to prevent CO2 leakage. Most probable leakage paths are constituted by the natural (faults) or artificial (around wells) interfaces. In this study, the effects of the presence of carbon dioxide on the behaviour of a particular interface are considered. A chemo-poro-mechanical model for the excavated damaged zone located at the interface between the injection well cement and the caprock has been developed. This constitutive model accounts for the precipitation of calcium carbonates coming from the carbonation of the well cement. Crystallisation pressure induced by these carbonates modifies the stress state in the materials at the interface. The model couples a simplified chemistry of carbonates precipitation with a poro-mechanical model accounting for damage of geomaterials due to tensile stress states. This poro-mechanical model is developed at the macroscale but an insight into the material's microstructure is also included through a description of the material's pore size distribution and its evolution with crystallisation and damage.