Fig. 2.

Modelling stages computed by the Storage Security Calculator. The immobilisation and leakage models described in Fig. 1 are integrated in the Storage Security Calculator to compute the proportion of remaining mobile CO₂ in the subsurface in four stages. I) The total amount of CO₂ injected into reservoir is computed (based on the storage target). II) The amount of CO₂ immobilised by residual trapping is calculated (residual trapping immobilisation model – [1a]). III). The amount of CO₂ leaked from the reservoir (and, for simplicity, assumed to reach the atmosphere) is calculated via the leakage model. IV) The amount of CO₂ immobilised by chemical trapping (chemical trapping immobilisation model) is calculated as a function of free-phase (i.e., both residual and mobile) CO₂ remaining in the reservoir. The calculations are carried out annually for each time-step of the model until there is no mobile CO₂ remaining, or until 10,000 years, whichever happens first