Experimental Characterization of Clay-rich Shales Dehydration by Dry ScCO2

The storage of CO2 in deep geological reservoirs relies on the integrity of the caprock to retain the buoyant CO2 plume from rising up to the surface. Laboratory studies of chemical and physical alterations of the caprock exposed to CO2 (dry and in supercritical state) are relevant to predict the long term evolution of the system. In this study, we performed a series of laboratory experiments in order to characterize the dehydration of clay minerals, which may be the main constituent of shale caprocks, and investigate possible surface alteration of the rock with dry CO2. Borehole core samples of the Draupne formation from the North Sea are exposed to dry CO2 near supercritical conditions (70 bars and 30 oC) in a batch reactor during 14 days. Several technics have been applied to document the dehydration of the clay minerals. Compacted powder tablets from the same rock sample have been generated in order to study surface alteration. The tablets show larger surface porosity after exposure to CO2 and could reflect a possible physical alteration of the caprock in contact to dry scCO2.