Experimental Investigation on Fracture Propagation in Heat-Treated Granite Samples During True Triaxial Temporary Plugging and Diversion Fracturing

Abstract Temporary plugging and diversion fracturing technology plays a critical role in improving the efficiency of deep geothermal resource extraction, particularly in hot dry rock formations, which are predominantly composed of granite. However, due to the deep burial, high temperatures, and high-stress conditions of hot dry rock, existing research has largely overlooked the mechanics of artificial fracture propagation during temporary plugging and diverting fracturing under high-temperature conditions. This study addresses this gap by using a true triaxial hydraulic fracturing physical simulation test system to investigate the impacts of temperature and stress on the temporary plugging and diverting fracturing of granite. The experiments revealed the variation patterns of two-stage breakdown pressure and the mechanisms of fracture diversion and propagation in granite under high-temperature conditions. Key findings indicate the existence of a critical stress difference for fracture diversion, where artificial fractures in granite will redirect and propagate if the local stress difference falls below this threshold. Additionally, the breakdown pressure decreases as temperature rises but increases with greater horizontal stress differences. The frequency of pressure fluctuations during injection also rises with temperature, suggesting that higher temperatures prolong the sealing effect of the temporary plugging agent. The data show that when the horizontal stress difference increases by 10 MPa at 25 °C, the injection pressures during the first-stage water fracturing and second-stage temporary plugging fracturing increase by 56.9% and 90.2%, respectively. At a 2.5-MPa horizontal stress difference, the angle between the fractures created in the first and second stages is largest, approaching 90 deg. Under constant stress, higher temperatures lead to larger diversion angles, indicating that higher temperatures promote the development of more complex fracture networks in hot dry rock. These findings offer valuable theoretical insights and practical guidance for optimizing hydraulic fracturing techniques and enhancing the efficient development of deep geothermal resources.