Experimental study on the characteristics and mechanism of high-pressure water jet fracturing in high-temperature hard rocks

Rock breaking using a high-pressure water jet is an emerging drilling technique for high-temperature deep-ground resources. The damage characteristics associated with using a water jet in high-temperature hard rocks were significantly different from those at room temperature. In order to explain the fracturing mechanisms associated with this robust drilling technology, the author conducted jet impact tests on granite and shale at varying temperatures to determine the crushing characteristics of these rock samples. The 3D reconstruction technology was utilized to characterize the internal 3D damage field and to analyze the fragmentation mechanisms of two high-temperature hard rock samples. According to this study, the degree of rock fragmentation at high-temperature condition was significantly greater than that associated with the heating-cooling and room temperature conditions. Thermal shock stress promoted large volume lamellar fractures of granite and shale, but there are maximum damage temperature conditions in shale. The stress wave and thermal stress caused by dynamic load act synergistically to cause rock mass peeling. Microscopically, the fracture characteristics of the rock samples were also examined by SEM, and quartz grains of high-temperature shale were observed to be exfoliated from their heterogeneous surroundings.