In this work, we present the results of a new in situ experiment to complete the existing scientific dataset on well integrity in the context of CO2 storage. This experimentation has been designed to evaluate the sealing behaviour of a monitored well after mechanical and chemical stresses due to pressure and temperature changes (stage A) and due to the exposure to carbonated brine (stage B), before a final overcoring stage for retrieving the well system and the surrounding clay. The stage A has been the subject of a first publication (Manceau et al., 2015; Water Resour. Res., 51, 6093–6109) and the two latter stages are described in this paper. Multidisciplinary methods (hydraulic tests and modelling, fluid sampling and modelling, analysis of cement and clay samples on the overcore) are used to get better insight, in a realistic wellbore context, on the interplay between the geochemical questions, and the operational and construction issues. In particular, this study shows that when good integrity pre-exists before a well is in contact with carbonated water, the exposure to dissolved CO2 does not seem to lead to a degradation of the well hydraulic properties but rather to their improvement.