Strength, energy evolution and cracking process of sandstone under high-temperature and high-pressure coupled true triaxial compression

High temperature and high-stress environment significantly impact the mechanical properties of rocks in the deep underground. In this paper, the true triaxial compression tests were carried out to explore the impact of principal stresses and temperature on the mechanical properties and cracking characteristics of sandstone from Sichuan province China using the self-developed real-time high-temperature true triaxial test system. Four groups of laboratory tests were carried out, with minor principle stress ranging from 4 to 70 MPa, intermediate principle stress ranging from 6 to 200 MPa, and temperatures ranging from 26 to 200 celcius, on two dozens of Longchang sandstone samples. The complete stress-strain curves were obtained, and the strength, deformation, brittleness, and cracking mode at the failure were analyzed for the sandstone under different principal stresses and temperatures. It indicates that the angle of the sandstone failure plane decreases monotonically with the increase of the minimum principal stress, and shows no obvious relationship with the intermediate principal stress. The deformation modulus and featuring stresses of the sandstone increase first and then decrease with the increase of temperature in the range from 26 to 200 celcius and reach the maximum value at 90 degrees C. The crack initiation in the sandstone before the peak induced by true triaxial stress loading seems to be delayed in temperatures lower than 90 celcius while accelerated in those higher than 90celcius by the temperature increase. The results provide references for the high-temperature cracking of sandstone reservoirs in the field and data support for the corresponding numerical models.