| Popis: |
Thermally-induced changes in the fracture properties of geological reservoir rocks can influence their stability, transport characteristics, and performance related to various deep subsurface energy projects. The modified maximum tangential stress (MMTS) criterion is a classical theory for predicting the fracture instability of rocks. However, there is a lack of research on the accuracy of MMTS theory when rocks are subjected to different temperatures. In this study, mechanical theoretical analysis and failure and fracture mechanics experiments of granite under the influence of temperatures ranging from 20 °C to 600 °C are carried out. The results showed that the theoretical estimated value of MMTS differs significantly from the experimental data at 20 °C−600 °C. The Keff/KIC ratio is less than the experimental test value due to the critical crack growth radius (rc) estimated by the conventional method being larger than the critical crack growth radius (rce) derived from the experimental data. Varied temperatures affect the fracture process zone size of fine-grained, compact granite, and the MMTS theoretical estimation results. Therefore, it is essential to modify the critical crack growth radius for MMTS theory to accurately predict the fracture characteristics of thermally damaged rocks. In addition, the variation of the rock’s mechanical properties with temperature and its causes are obtained. Between 20 °C and 600 °C, the mode-I, mode-II, and mixed-mode (α = 30° and 45°) fracture toughness and Brazilian splitting strength of the granite decrease by 80% and 73%, respectively. When the rock is heated above 400 °C, its deterioration is mainly caused by a widening of its original cracks. |
