Numerical Study of Thermo-Mechanical Effects on the Viscous Damage Behavior of Rock Salt Caverns

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Date
2017-06Author
Cheng, Zhu
Shen, Xianda
Arson, Chloé
Pouya, Ahmad
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Underground cavities in rock salt have received increased attention for the storage of oil, gas, and compressed air
energy. In this study, the transition between secondary and tertiary creep in salt is determined by a micro-macro model: The
initiation of grain breakage is correlated with the acceleration of viscoplastic deformation rate and with the initiation of damage at
the macroscopic scale. Salt stiffness decreases when macroscopic damage increases, which allows predicting the evolution of the
damage zone around salt caverns used for geological storage. After implementing the phenomenological model into the Finite
Element Method (FEM) program POROFIS, two thermo-mechanical coupled stress paths are simulated to analyze stress
concentrations and viscous damage around a 650-m-deep cavern in axisymmetric conditions. Numerical results indicate that,
despite the pressurization or depressurization-induced temperature variation, internal gas temperature always tends to approach the
primary surrounding rock mass value. The viscous deformation induced by thermo-mechanical couplings significantly affects the
original stress field at the cavern wall and induces high damage at the most concave sections of the cavern. Results reveal the
significant influences of idle time, gas pressure range, and injection and withdrawal cycles on stress, strain and temperature
distributions in the vicinity of the cavern. More analyses are needed to confirm the influence of thermo-mechanical cycles of
pressurization and depressurization, and to design long-term cavern operations.