Abstract

Rock salt is a very complex material. Simulation of the non-linear and time-dependent mechanical behavior of salt caverns requires advanced constitutive models, relevant sets of parameters and accurate numerical computations. No well-known software packages were designed initially for salt caverns; they had to be adapted by the end user due to the unusual behavior of salt compared to other rocks. Most of the time, cavern thermodynamics, salt geomechanics and hydraulics cannot be calculated simultaneously. Some software packages are limited only to rock/soil mechanics and thermal computations —they include no cavern thermodynamics. However, coupling cavern thermodynamics and rock mechanics is essential when considering problems such as fast cycling in a gas cavern, the storage of hydrogen or compressed air, or for modeling of the long-term behavior of caverns. A case-by-case study must be performed for all new projects, taking into account relevant creep and also considering sets of parameters that were calibrated accurately in the laboratory — or better, from on-site tests performed in an existing borehole or cavern. This paper introduces the main features of salt-rock mechanics and salt-cavern thermodynamics. A simple example of a cycled hydrogen cavern experiencing a blowout is presented.

Introduction

Storage of gaseous and liquid hydrocarbons in salt caverns is a mature technology. More than 2000 caverns are operated worldwide. Storage of electricity as compressed air in salt caverns (CAES) is possible; two caverns have been operated for this purpose since the 1970s, and a couple of new projects are under development (Koopmans et al., 2022). There also are many ongoing projects related to hydrogen storage (Fig. 1). Salt caverns initially were designed, created and operated using very limited modeling tools. The complexity of rock-salt behavior and of cavern thermodynamics appeared gradually.

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