Experiment investigation of granite damage under the high-temperature and high-pressure supercritical water condition

Geothermal energy has the potential to produce significant amounts of electricity. Hot dry rock, stored abundant geothermal energy, is mainly made up of granite and hard to drill. Hydrothermal spallation drilling (HSD) is suitable to drill in hard granite formation. The granite breakage in HSD means the granite is induced to spall under high-temperature and high-pressure supercritical water condition, which is a key problem in HSD application. In this paper, we investigated the effect of supercritical water on granite damage by experiment. First, the granite samples were heated under the supercritical water condition. Meanwhile, another granite samples were also heated by air for comparison. After that, abundant post processing tests were conducted to compare the three type of granite samples: samples heated by supercritical water, samples heated by air and original samples. Specifically, the mineral analysis, uniaxial tensile test, uniaxial compression test, acoustic wave test was conducted to quantitatively investigate the granite damage. Meanwhile, thin section observation and scanning electron microscope observation were conducted to investigate the fracture distribution in the samples after damage. This study can provide useful insight into the granite damage heated by supercritical water, which can help to optimize the design of HSD in field application.