Study on thermodynamic behaviour of natural gas and thermo-mechanical response of salt caverns for underground gas storage

Using salt caverns for underground gas storage (UGS) is an important energy storage solution. A coupled aero-thermo-mechanical (ATM) model with an integrated wellbore–3D realistic cavern geometry was established to investigate the thermodynamic behaviour of natural gas and the thermo-mechanical response of rock salt for UGS caverns. Unlike classical thermo-gas-mechanical (TGM) models that assume the cavern gas is an ideal gas and in an isotropic thermodynamic state, the ATM model solved thermodynamic properties for the real gas, and revealed the tempo-spatial varying gas state and its mechanism. Predictions of gas temperature, pressure and flux by ATM modelling well captured the in-situ measurements obtained by the distributed optical cable monitoring system during a one-month field testing at Jintan UGS site. Effects of the tempo-spatial varying gas state on the mechanical response were unveiled by ATM modelling. Predictions of mechanical response by TGM modelling shared similar patterns as that by ATM modelling, however, the TGM model tended to underestimate the risk of creep failure, tensile failure, fatigue failure and plastic damage due to the isotropic gas state. The proposed model could be used to improve the thermodynamic and mechanical predictions that are pertinent to the optimal design and the stability of caverns.