Temperature-dependent factors on hydraulic fracturing of hot dry rock (HDR): An experimental investigation

Abstract

Hot dry rock (HDR) is rich in geothermal energy and renewable and does not cause pollution; therefore, it has attracted considerable research attention. Previous studies have extensively discussed the process of HDR hydraulic fracturing based on the crack initiation mechanism, initiation pressure, and crack propagation law. However, the temperature-dependent factors (thermal damage and thermal shock) affecting the HDR hydraulic fracturing process have not been specifically discussed. Therefore, HDR hydraulic fracturing tests with different sample temperatures and injection rates were designed in this study. Further, various factors affecting the hydraulic fracturing related to temperature, including the thermal damage, thermal shock, and injection rate, were analyzed. The test results indicate that under the condition of variable temperature parameters, thermal damage and thermal shock caused the initiation pressure of the reservoir to decrease with the increasing temperature. The degree of weakening increased with the increasing temperature. After fracturing, the initial fracture in HDR continued to expand under the action of thermal shock and residual pressure, and the fracture expansion scale increased with the increasing temperature. Under the condition of variable fracturing parameters, microfractures with large areas were more likely to form when fracturing occurred at a lower injection rate, which is beneficial to improve the heat exchange efficiency of the reservoir and avoid short circuits. These research results provide a scientific explanation for the influencing factors of HDR hydraulic fracturing and offer geological and engineering guidance for optimizing the hydraulic fracturing in an enhanced geothermal system.