The effect of thermal stresses on the relation between rock failure and temperature and pressure of supercritical carbon dioxide jet

Abstract

AbstractThe supercritical carbon dioxide (SC‐CO2) jet is a new‐type of rock‐breaking method that effectively combines pressure impact and thermal shock. Current studies show that a carbon dioxide jet produces a larger damaged area and requires a lower threshold pressure for rock breaking compared to a water jet; however, the rock‐breaking mechanism of the SC‐CO2 jet has not been clearly explained. This study developed a heat‐fluid‐solid coupling model using ANSYS. The simulation and experimental results show good agreement, clearly explaining the effect of thermal stress in the rock breaking of the SC‐CO2 jet. The study shows that the temperature field of the SC‐CO2 jet could result in an increase in the maximum stress and the high‐stress area. The thermal gradient between the rock surface and the internal parts decreases with jet time, further contributing to lower rock stress. When jet temperature and jet pressure differences at the entrance/exit increase, the jet temperature field contributes more to the increase in rock stress. For hard rocks with a higher elastic modulus, the thermal gradient can reduce the depth of high stress in the rock's interior and lead to greater stress on the rock surface. The study provides a basis for employing the SC‐CO2 technique in well drilling and in fracturing for shale gas exploitation. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.