Non-constant evolution of mixed mode fracture process zone in heat-treated salt rock during the whole loading

Exploring the evolution of the fracture process zone (FPZ) in mixed fracture within salt rock is vital for enhancing our comprehension of salt rock fracture properties and assessing the long-term stability of energy reservoirs. Prior research has identified the existence of constant evolution within the FPZ, a topic that has sparked debate. For this purpose, we acquired data on the evolution of the FPZ during the whole loading process of mixed fracture in salt rock at different temperatures by employing Digital Image Correlation (DIC) technology. After the experiments, we employed the computerized tomography (CT) scanning technique to analyze the pore structure within the mixed-mode salt rock fracture. This analysis aims to provide further insights into the impact of temperature on the evolution of the FPZ. The findings demonstrate that the evolution of the FPZ in mixed mode salt rock fracture exhibits non-constant behavior, involving intricate evolutionary processes. When the specimen was subjected to a temperature of 700 degrees C and an angle of 10 degrees, the length of the FPZ increased from 0.4 mm to 10.7 mm, before decreasing to 9.2 mm. Moreover, during the whole loading process, the non-constant evolution of the FPZ is notably influenced by temperature. Notable variations in the evolution of the FPZ emerged during the whole loading process, especially when the temperature was below 400 degrees C, as opposed to when it exceeded 500 degrees C. When the temperature exceeded 500 degrees C, the FPZ emerged at an earlier stage. At a temperature of 700 degrees C, the FPZ emerged in the 30 % pre-peak stage of the process. Additionally, during the post-peak stage, a more complex and non-constant evolution was observed. A bilinear relationship between the length of the FPZ and temperature at the peak load stage was observed.