Micro-characteristics of granite impinged by abrasive water jet from a mineralogical perspective

An abrasive water jet (AWJ) is commonly used to develop deep geothermal resources, such as drilling in hot dry rock (HDR). The influence of rock mineral properties, such as mineral types, mineral contents, and grain size, on the formation of perforation by AWJ is unclear yet. In this study, we investigate AWJ impacts on three types of granite samples with different mineral fractions using a polarizing microscope and scanning electron microscope (SEM). The results show that when the grain size is doubled, the perforation depth increases by 16.22% under the same type of structure and properties. In general, fractures are more likely to be created at the position of rough surfaces caused by abrasive impact, and the form of fractures is determined by the mineral type. In addition, microstructure analysis shows that transgranular fractures typically pass through large feldspar particles and quartz removal occurs along mineral boundaries. The longitudinal extension of perforation depends mainly on the strong kinetic energy of the jet, while the lateral extension is controlled by the backflow. The results contribute to a better understanding of the process involved in the breaking of hard rock by abrasive jets during deep geothermal drilling.