A poromechanical model is developed to identify how chemical reactions of carbonation may impact the mechanical behaviour of wellbore cement in the context of CO 2 storage. The model enables the evaluation of pore overpressure, porosity and solid-skeleton strain evolutions during the carbonation process. The major chemical reactions occurring within cement and their consequences on the volumes of dissolved cement matrix and precipitated carbonate are identified. This information is imported into a poromechanical model and the risk of damage is estimated through the calculation of the free energy stored within the solid matrix. A semi-analytical solution is proposed and applied to a simplified 1D cement carbonation example. The risk of damage of the cement structure submitted to intrusion of aqueous CO 2 is estimated. A set of parametric studies is carried out to investigate the effect of medium permeability and effective diffusion coefficient on the damage risk.