There are many research results on the changes in pore structures and physical parameters of rocks caused by high temperature, but the rock lithology in those studies is single, and the changes in physical properties and differential mechanisms of rocks with different lithologies after thermal stimulation are less researched. In this paper, the change patterns of porosity, permeability and acoustic velocity of rocks with different lithologies under high temperature are studied by performing laboratory experiments on the tight sandstone and mudstone of the Upper Triassic Xujiahe Formation and the shale of the Lower Silurian Longmaxi Formation in the Sichuan Basin. In addition, the relationships of dynamic elastic parameters, fracture density and damage coefficient of rocks with different lithologies vs. temperature are discussed. And the following research results are obtained. First, rocks with different lithologies are different in the threshold temperature, with sandstone at 500 ℃, shale at 400 ℃, and mudstone at 300 ℃. Second, as the temperature increases, the surface color of rocks with different lithologies gradually changes, the macroscopic volume gradually increases, and the quality and density gradually decrease. The total organic carbon (TOC) is the main factor affecting the apparent color of shale. Third, with the increase of temperature, the porosity, permeability, fracture density and damage factor of rocks with different lithologies increase, while the elastic parameters such as acoustic velocity, elastic modulus, bulk modulus and shear modulus show a decreasing trend. Fourth, as the temperature increases, the time-domain signal amplitude of the shale decreases, and the main frequency of the frequency-domain map gradually shifts towards the low-frequency part, resulting in an increase in the change degree of rock pore structure; Fifth, the quality loss of rocks with different lithologies is affected more by clay minerals during the initial heating period, but by the content of carbonate minerals under high temperatures. The content of carbonate minerals has a positive effect on the increase of porosity, while the content of quartz has a positive effect on the increase of permeability. The higher the content of quartz and carbonate minerals in the rock, the better the improvement effect of petrophysical properties after high-temperature treatment. In conclusion, the influence degree of high temperature on the petrophysical properties is mainly dependent on the mineral components of rocks themselves. The research results have a certain reference value for the feasibility study of in-situ heating modification technology in reservoir permeability enhancement. © 2023 Natural Gas Industry Journal Agency. All rights reserved.
