Phenomena at interface of saline aquifer and claystone caprock under conditions of CO₂ storage

When modelling the impact of the hydrogeochemical processes of CO₂ sequestration on the contact zone of a saline sandstone aquifer and a claystone caprock in the Upper Silesian Coal Basin, small decreases in porosity were noted, visible mainly in the aquifer rocks. They were due to the degradation of kaolinite, albite and muscovite, and the recrystallization of K-feldspar and quartz. The porosity of the caprock remained almost unchanged, which was to the advantage of the integrity of the repository. In major parts of the aquifer and caprock zone, the mineral trapping of CO₂ has beneficial effects, but at the interface of the aquifer and the insulating layer, in the basal part of the caprock, a release of carbon dioxide may occur temporarily, associated with the dissolution of calcite.