Abstract
Due to the extremely low permeability and the excellent creep behavior, rock salt is the optimal surrounding rock of underground energy storage. The long-term safe operation of the rock salt energy storage is closely related to the creep behavior and long-term strength of rock salt, but few researches focus on the long-term strength of rock salt. In order to more accurately predict the long-term strength of rock salt, the isochronous stress–strain curve method and the volume expansion method for determining the long-term strength were analyzed and discussed based on axial compression tests and axial creep tests. The results show that the isochronous stress–strain curve method is intuitive but will greatly increase the test cost and test time to obtain a satisfactory result. The volume expansion method is simple, but the long-term strength obtained according to the inflection point of volumetric strain is much greater than the actual long-term strength of rock salt. Therefore, a new method applicable to rock salt was proposed based on the evolution of damage in rock salt in this paper, which takes the corresponding stress value at the damage initiation point as the long-term strength. The long-term strength determined by this method is consistent with that by the isochronous stress–strain curve method. The method is more economical and convenient and aims to provide a reference for the long-term stability study of underground salt caverns.
Highlights
Underground storage of energy is an economical and safe way for storage of huge energy, like oil, natural gas, hydrogen, pressured air etc
Rock salt has extremely low permeability [1,2,3,4] and excellent creep behavior, which can ensure the tightness of underground energy storage
The linear elastic volume strain curves can be obtained by using Equations (2–4), and the tangent point of the linear elastic volume strain curve and the volume initiation point and the stress corresponding to the inflection point of volumetric strain are listed in Isochronous stress-strain curve method
Summary
Underground storage of energy is an economical and safe way for storage of huge energy, like oil, natural gas, hydrogen, pressured air etc. Rock salt has extremely low permeability (permeability coefficient is less than 10–20 m2 ) [1,2,3,4] and excellent creep behavior, which can ensure the tightness of underground energy storage. Due to the stable mechanical properties and the ability to recover from damage of rock salt, it is able to adapt to pressure changes during the operation of the reservoir, which makes rock salt become an internationally recognized ideal place for underground energy storage [5]. The long-term safe operation of rock salt underground storage must inevitably involve the time-dependent properties of rock salt. The most important of these properties are long-term strength and creep, meaning that the two key issues in the long-term safe operation of rock salt underground storage are the long-term strength and creep characteristics of rock salt
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