Geomechanical stability of the caprock during CO2 sequestration in deep saline aquifers

Abstract

Suitable saline aquifers should be capped by a low-permebility caprock. This caprock may undergo large pressure buildup because of CO2 injection. This will affect the stress field and may induce large deformations, which can eventually damage the caprock and open up new flow paths. Hydromechanical (HM) simulations capture phenomena that purely hydraulic (H) codes cannot predict. These include the initial pressure drop in the caprock as a response to CO2 injection (Fig. 1) (Vilarrasa et al., 2010). Furthermore, failure mechanisms strongly depend on the initial stress state (Rutqvist et al., 2008). Unlike open aquifers, in which pressure buildup is limited because brine can migrate out laterally, semi-closed aquifers experience an additional pressure buildup. This additional overpressure depends on the caprock permeability. Relatively permeable caprocks (k<10-18 m2) diminish overpressure because brine can leak through them.