Wellbore stability in high-temperature granite under true triaxial stress

Supercritical/superhot geothermal success depends on successful drilling. However, wellbore stability in supercritical environments has not been investigated because imposing sufficient stress on high-temperature granite with true triaxial loading is difficult. We conducted wellbore failure experiments on 200–450 °C granite under true triaxial stress, including deformation and acoustic emission measurements, and post-experiment thin section observations. Wellbore failure initiated at stress states consistent with existing brittle failure criterion at the studied temperatures. Using breakout geometry for in situ stress estimation may be difficult as shear failure propagation is suppressed at high temperatures; however, boreholes may be inherently stable in high-temperature environments.