Clay-rich rocks as barriers for geologic CO₂ storage

In geologic CO₂ storage, it is important to find a proper barrier material that will avoid or limit acidic fluid migration. Shales that are ductile and have high capillary entry pressure and low permeability can be considered as good candidates for the caprock. Faults may contain high percentage of clay and act as barriers for fluid flow in reservoirs. Experimental techniques have been developed to characterize the behavior of clay-rich materials at elevated pressures. Intact and remolded specimens of Opalinus clay- A Jurassic shale from Switzerland- A re brought to the conditions of deep (> 1 km depth) geologic storage and fully saturated with in-situ brine. Poromechanical parameters and failure characteristics are measured in drained and undrained conventional triaxial compression experiments. CO₂ breaktrough pressure and permeability of shale are assessed in oedometric tests on thin (12 mm) samples. Experimentally measured parameters are used in numerical simulations to assess fault stability and the shaly caprock integrity for the case of geologic carbon storage, where cooling is likely to occur around injection wells. It is found that clay-rich faults may induce microseismic events, but without leading to CO₂ leakage.