Effect of Thermal Treatment on the Physical and Mechanical Properties of Sandstone: Insights from Experiments and Simulations

During oil and gas exploitation in tight sandstone reservoirs, the influence of temperature on the physical and mechanical properties of sandstone cannot be ignored, which is of great significance to the formulation of oil and gas exploitation techniques and the accurate evaluation of recovery. In this article, the physical and mechanical properties of sandstone after thermal treatment from 25 to 800 °C are investigated by laboratory tests. The experimental results indicate that 400 °C is a threshold, and the temperatures of less than 400 °C have little effect on the physical and mechanical properties of sandstone. Poisson's ratio has a sudden change between 400 and 600 °C, and this change can be attributed to the phase transition of quartz at 573 °C. As the temperature increases, the failure behavior of sandstone transforms from brittle to ductile. Subsequently, a Knuth–Durstenfeld shuffle algorithm is introduced to characterize the heterogeneity of rocks considering mineral composition, and this algorithm is verified to better reveal the thermal damage of rocks. The uniaxial compression test of sandstone after thermal treatment is a two-stage damage process, and this process is completely simulated in COMSOL. In addition, a fully coupled thermal–mechanical-damage constitutive model is established to predict the failure process of rocks. The ultimate failure modes of sandstone in the simulation are in good agreement with the experimental results, indicating the reliability of the proposed model.