Evaluation of risks in CO2 deep geological storage via a stochastic method

The deep geological storage of carbon dioxide (CO2) in deep saline aquifers is considered a promising countermeasure to the greenhouse effect. CO2 at supercritical conditions is injected in saline aquifer at depths larger than 800 m. The CO2-rich phase is lighter than brine and moves upward; therefore a capping geological seal (the caprock) is necessary for a safe storage. Preserving the integrity of the caprock is of paramount importance. The integrity can be compromised by pressure-induced new fractures or pressure-reactivated existing faults. These features may represent leakage paths to the biosphere. At a preliminary stage, the feasibility of a (unstructured) saline aquifer can be assessed by means of a risk analysis (RA). Given a simple geometrical scheme of the aquifer, the RA for the CO2 geological storage consists of the combination of a semi-analytical solution of the CO2 transport and criteria for the onset of fracturing and reactivation of existing faults. The parameters of the failure criteria are assumed conforming to specific Probability Density Functions (PDFs). The results from RA are synthesized in the probability of caprock failure and probability of fault reactivation. The results of an application example are illustrated herein.