STUDY ON CREEP CHARACTERISTICS OF SALT ROCK UNDER UNLOADING CONDITIONS

Abstract

The underground salt karst caverns are considered as an excellent oil and gas reserve site due to the dense low permeability and excellent creep. The creep characteristics of salt rocks under frequent gas injection and gas production activities are the focus of salt cavern gas storage. The 700h loading and unloading creep tests were performed on salt samples taken from Jintan, Jiangsu Province, China, and the creep behaviors of rock salt under different loading and unloading stress paths were compared and analyzed. The results showed that the steady-state creep strain rate increases with the increase of deviatoric stress during multi-stage creep test, The deviatoric stress has a great influence on the steady-state creep strain rate, and the steady-state creep strain rate increases obviously with the increase of the deviator stress in the loading stage, but in the unloading stage, steadystate creep strain rate increases with deviatoric stress increase, and the increase range is small. The Fractional Derivative model, the Nishihara model and the Burgers model are used to fit the experimental data of the initial creep stage and the steady-state creep stage during loading stage, the results show that the Fractional Derivative model can better describe the creep curve. The creep deformation curve is almost straight and the creep curve is fitted by a linear function in unloading stage, the results show that the fitting curve is consistent with the experimental results.