Experimental Study on the Uniaxial Creep Mechanical Properties of Salt Rocks

During the long-term operation of salt cavern gas storage, the duration of pressure changes within the reservoir is relatively long, and the frequency of pressure changes is relatively low. The deformation process of the reservoir’s surrounding rock is a creep deformation process under low-frequency cyclic loading. To deeply study the mechanical properties of salt rock under long-term creep conditions, three sets of uniaxial creep tests on salt rock were conducted. The test results show that: (1) For damaged salt rock samples, the deformation process is divided into three stages: decelerated deformation, stable deformation, and accelerated deformation. The corresponding stress-strain curve exhibits a trend of "sparse"-"dense"-"sparse". (2) Among the two influencing factors of loading rate and stress upper limit, the stress upper limit has a more significant impact on the mechanical properties of salt rock. Under the same stress amplitude, as the number of cycles increases, the impact of different loading rates on salt rock deformation gradually decreases. (3) During the loading stage, the deformation rate of the salt rock samples gradually decreases over time until the stress increases to 60% of the stress amplitude, at which point the strain rate starts to increase. (4) In the constant stress upper limit stage, the strain rate gradually decreases over time, but significantly increases when the sample is close to failure. (5) Throughout the test process, the strain rates during different cycles are nearly equal in both the loading stage and the constant stress upper limit stage. In the final cycle before sample failure, the strain rate in the constant stress upper limit stage increases noticeably. (6) In the unloading stage, the deformation rate increases as the load decreases, with the elastic strain of the salt rock recovering in this stage, showing a negative deformation rate. (7) During the constant stress lower limit stage, the strain rate is close to 0 and fluctuates in a negative value state.