The full-scale deployment of underground storage of CO 2 in permeable sedimentary reservoirs depends strongly on the sealing capacity of the caprocks and wellbore cement that may be degraded leading to hydraulic discontinuities. Remediation technologies consisting in rebuilding the sealing capacity of the degraded material, or adding a new sealing layer, is a critical issue as part of the risk mitigation procedure required for underground CO 2 storage. Actually, engineered Portland cement injection is the foremost available industrial technique; however, alternative products offering, for instance, better injection properties, are currently investigated with variable success so far. In this study, a new technique aimed at using a low viscosity hydrated solgel as sealant product in case of leakage is presented. Its low cost, high injectivity capacity and low density of the hydrated product (hydrogel) makes this technique attractive. The solgel synthesis was optimized for (1) reducing energetic and material costs; (2) improving the chemical and mechanical properties of the emplaced product and (3) controlling the duration of the aging process in order to form a solid hydrogel after a few days. Permeability tests that consisted of injecting the synthesized solgel in different porous media confirmed the sealant capacity of the emplaced hydrogel to significantly reduce rock permeability.