Experimental Study on the Dynamic behavior and Energy Consumption of Hot Dry Rock under True Triaxial Condition

Abstract

During percussion drilling in deep geothermal reservoir, the high strength of the bottom hole rock (mainly hot dry rock, HDR) resulting from the high three-dimensional in-situ stress leads to a low rate of penetration (ROP). Limited by the previously experimental technique, the dynamic behavior and failure mechanism of HDR under high strain rate and true triaxial stress condition are still unclear. By means of the three-dimensional split Hopkinson pressure bar (3D SHPB) system, the dynamic response of HDR (replaced by granite) is study. Compared with the traditional Hopkinson device, the true triaxial static load can be imposed to a cubic specimen before testing to simulate the confining pressure state in deep well by the 3D SHPB system. The results show that the greater the loading strain rate, the higher the dynamic strength, the shorter the failure time and the greater the energy consumption. Based on the theory of impact damage, the dynamic constitutive model and energy consumption model of rock under impact and true triaxial stress condition are established. The dynamic strength, failure time and energy consumption of HDR under true triaxial stress have a significantly strain rate correlation, and that express as power function consist with the damage models. The variation laws of elastic parameters of HDR with the strain rate and three-dimensional static stress are analyzed. Combined with the established damage models, the empirical formula for predicting the dynamic energy consumption of HDR in percussive drilling is obtained. This study is helpful for the efficient rock breaking method and theoretical research in deep geothermal reservoir.