The influence of impurities and fabrics on mechanical properties of rock salt for underground storage in salt caverns – a review

Salt caverns are used for the storage of natural gas, LPG, oil, hydrogen, and compressed air due to rock salt advantageous mechanical and physical properties, large storage capacity, flexible operations scenario with high withdrawal and injection rates. The short- and long-term mechanical behaviour and properties of rock salt are influenced by mineral content and composition, structural and textural features (fabrics). Mineral composition and fabrics of rock salt result from the sedimentary environment and post sedimentary processes. The impurities in rock salt occur in form of interlayers, laminae and aggregates. The aggregates can be dispersed within the halite grains or at the boundary of halite grains. Mineral content, mineral composition of impurities and their occurrence form as well as halite grain size contribute to the high variability of rock salt mechanical properties. The rock or mineral impurities like claystone, mudstone, anhydrite, carnallite and sylvite are discussed. Moreover, the influence of micro fabrics (in micro-scale) like fluid inclusions or crystals of other minerals on rock salt mechanical performance is described. In this paper the mechanical properties and behaviour of rock salt and their relation to mineral composition and fabrics are summarised and discussed. The empirical determination of impurities and fabrics impact on deformation mechanism of rock salt, qualitative description and formulation of constative models will improve the evaluation and prediction of cavern stability by numerical modelling methods. Moreover, studying these relations may be useful in risk assessment and prediction of cavern storage capacity.