Comprehensive characterization of rock salt from the Haselgebirge Formation: Insights for cavern storage of hydrogen

Solution mining of salt is commonly used in the Austrian Haselgebirge Formation and after-lifetime utilization of the existing caverns for storage of energy carriers is increasingly discussed. Cavern storage could play a key role e.g. in the future establishment of a hydrogen supply network. The Haselgebirge Formation, however, is a challenging engineering environment as it is tectonically deformed, resulting in strongly heterogeneous salt bodies with unclear mechanical and petrophysical properties. To provide a first assessment for future storage applications, two abundant salt rock types (clean red salt vs anhydrite rich grey salt) have been characterized regarding their mineral composition (X-ray diffraction), texture (computed tomography, scanning electron microscopy), porosity, and permeability. After the baseline characterization, multi and single stage triaxial tests have been conducted in 70% relative humidity to test for nitrogen gas breakthrough behavior of the different lithologies in order to simulate a gas storage operation. Despite a gas breakthrough at low confinement pressure (1MPa), the samples of both lithologies stayed gas tight at 25 MPa confinement pressure until a maximum differential stress of 30 MPa which is five times the potential storage pressure of 6 MPa in a depth of 300 m. Furthermore, considering the low permeability values for both clean red and heterogeneous grey salt (<10^-17m²), the tested salt rock types can be considered effective seals for hydrogen storage.