Mineralogy, microstructures and geomechanics of rock salt for underground gas storage

Abstract

Rock salt has excellent properties for its use as underground leak-proof containers for the storage of renewable energy. Salt solution mining has long been used for salt mining, and can now be employed in the construction of underground salt caverns for the storage of hydrogen gas. This paper presents a wide range of methods to study the mineralogy, geochemistry, microstructure and geomechanical characteristics of rock salt, which are important in the engineering of safe underground storage rock salt caverns. The mineralogical composition of rock salt varies and is linked to its depositional environment and diagenetic alterations. The microstructure in rock salt is related to cataclastic deformation, diffusive mass transfer and intracrystalline plastic deformation, which can then be associated with the macrostructural geomechanical behavior. Compared to other types of rock, rock salt exhibits creep at lower temperatures. This behavior can be divided into three phases based on the changes in strain with time. However, at very low effective confining pressure and high deviatoric stress, rock salt can exhibit dilatant behavior, where brittle deformation could compromise the safety of underground gas storage in rock salt caverns. The proposed review presents the impact of purity, geochemistry and water content of rock salt on its geomechanical behavior, and thus, on the safety of the caverns.