The mechanism of granite breaking by electric pulse under high temperature and high pressure environment

Abstract High‐voltage electric pulse drilling technology has the advantages of high rock‐breaking efficiency, and low rock‐breaking energy consumption, which is one of the most promising rock‐breaking methods in geothermal drilling. However, there is insufficient understanding of the mechanism of high‐voltage electric pulse breaking of HDR under high‐temperature and high‐pressure environments (HTHP). In this paper, a numerical simulation model of electric breakdown under HTHP is constructed, and the whole process of high voltage electric pulse rock‐breaking and plasma channel generation is realized from the seven‐field coupling of circuit field, current field, magnetic field, breakdown field, heat transfer field, solid mechanics field and flow field. The temperature changes in the rock during the electric pulse rock‐breaking process were comprehensively analyzed, and the effects of different initial rock temperatures (200°C, 300°C, 400°C) and surrounding pressure conditions (30, 60, 90 MPa) on the high‐voltage electric pulse rock breaking law were considered. It is found that the thermal conductivity of the rock shows an increasing and then decreasing trend as the initial temperature of the rock increases, and that the thermal conductivity has a tendency to guide the development of plasma channels, and the radius of the plasma channels increases with the increase of the initial temperature of the rock. The heat transfer generated by high‐voltage electric pulse rock breaking is mainly in conduction, and the distribution shape of conduction heat is similar to the shape of the breakdown channel. The research in this paper can provide theoretical and technical guidance for developing electric pulse rock‐breaking technology.