A proper risk management scheme for CO2 storage should include an adequate monitoring plan completed with a site-specific intervention plan in order to demonstrate that any undesired consequence can be prevented, if not corrected. We consider the case of brine, possibly followed by CO2, migrating from the storage reservoir to an overlying aquifer through a leaking abandoned well. The detection of such leakage may be done through pressure gauges, in which case the stopping of the injection and the sole pressure relief may be enough for preventing a CO2 leakage. In case of a late detection (e.g. though seismic surveys), the leakage may require implementing active corrective measure, e.g. a hydraulic barrier, for ensuring an efficient stop of the leakage and trapping the secondary accumulation. The design of this hydraulic barrier should consider operational constraints and mechanical integrity in order not to impact the shallower formations with the corrective measure.
