Fracture characteristics and thermal damage mechanism of shale under microwave radiation

This study investigates the effects of microwave radiation on the fracture characteristics and thermal damage mechanisms of shale. Microwave heating response tests were conducted on Shuigoukou Formation shale to examine its heating characteristics under varying microwave irradiation durations. Fracture toughness tests were performed to assess the impact of different bedding angles on shale fracture toughness and to elucidate the failure modes of shale at various bedding orientations. Results reveal that shale fracture toughness exhibits temperature thresholds under microwave action, which vary with bedding angle. For crack-splitter, crack-arrester, and crack-divider type shales, the temperature thresholds were determined to be 50 °C, 125 °C, and 200 °C, respectively. The fracture toughness decreases sequentially from crack-divider to crack-arrester to crack-splitter type shales, with all types showing a reduction as microwave radiation time increases. The thermal damage observed in shale under microwave heating correlates with the wave-absorbing characteristics of its various components. Moisture content, dielectric constant, and mineral composition were identified as the primary factors influencing the microwave thermal effect on shale. The findings contribute to a deeper understanding of the structural damage characteristics and fracturing mechanisms of shale reservoirs during thermal stimulation.