CO2 leakage is a major concern for geologic carbon storage. To assess the caprock sealing capacity and the strength of faults, we test in the laboratory the rock types involved in CO2 storage at representative in-situ conditions. We use the measured parameters as input data to a numerical model that simulates CO2 injection in a deep saline aquifer bounded by a low-permeable fault. We find that the caprock sealing capacity is maintained and that, even if a fault undergoes a series of microseismic events or aseismic slip, leakage is unlikely to occur through ductile clay-rich faults. © 2017 The Authors. Published by Elsevier Ltd. V.V. acknowledges financial support from the “TRUST" project (European Community's Seventh Framework Programme FP7/2007-2013 under grant agreement n. 309607) and from “FracRisk" project (European Community's Horizon 2020 Framework Programme H2020-EU.3.3.2.3 under grant agreement n. 640979). R.M. acknowledges partial support from the Center for Geologic Storage of CO2, an EFRC funded by the U.S. DOE, Office of Science, BES, under Award DE-SC0C12504. Peer reviewed