Damage Evolution and Acoustic Emission Characteristics of Salt Rock under Uniaxial Compression

Salt rock has low permeability, good creep characteristics, and damage recovery function. It is an important medium for oil and gas storage. However, during the injection and production operation of salt cavern gas storage, salt rock deformation has mechanical behavior such as large deformation, which affects the security of gas storage. The MTS815 rock mechanics testing system was used to conduct uniaxial compression experiments on different types of salt rocks, and the acoustic emission monitoring system was used to monitor the entire process of the experiment. The mechanical characteristics and acoustic emission characteristics of the salt rock deformation and failure process were studied, and the damage evolution characteristics were explored. The results show that: (1) the presence of interlayers in the salt rock samples can significantly increase its compressive strength. Through the comparison of the average compressive strength of the three sets of experimental cores, it is found that the interlayer strength in the salt rock can increase by 20%. The emission event is relatively calm below 40% of the compressive strength, and the acoustic emission event increases sharply when the value exceeds this value. (2) The damage evolution process of the corresponding core can be obtained by studying the spatial location of the acoustic emission event: small cracks occur everywhere. With the increase of stress, the expansion and connection of small cracks mainly occur in areas with high mud content, and macro-cracks are formed in this area; the failure of interbedded salt rocks first occurs in the hard interbeds, and then expands to the salt rock formations. Finally, it penetrates the salt rock layer and loses its bearing capacity; the pure salt rock is first damaged in the middle of the sample, and then transferred to both ends, but the damage is mainly concentrated in the middle of the sample, and finally forms a macroscopic fracture surface. (3) The accumulated energy values are used to establish the damage variable, and the evolution curve of the damage variable is divided into four parts, and the safety warning threshold of the project is proposed.