The partial electrical breakdown mechanism by high voltage electric pulses in multi-fractured granite

Abstract

High-voltage electric pulse (HVEP) technology has currently become a new efficient rock breaking method. In order to reveal the influence of internal fracture characteristics of heterogeneous granite on electric pulse rock breaking, the two-dimensional numerical model of multi-physical field coupling electrical breakdown of fractured rock is established, which the high-voltage electric pulse plasma generation in multi-fractured heterogeneous granite is realized from the coupling of circuit field, current field, breakdown field, heat transfer field and solid mechanics. This paper analyzes the influence of fracture porosity, fracture types and granite heterogeneity on the electrical breakdown of rock (i.e. the formation of plasma channel inside the rock). At the same time, the two-dimensional numerical model of electrical breakdown parameters, which considers the circuit structure parameters of the pulsed tool, the initiation and development of the electrical breakdown, the dependence between electrical breakdown intensity and time, and rock heterogeneity, are analyzed. The simulation results indicate that with the heterogeneity H of granite changing, the plasma channel inside the rock samples are different, while the time required for breakdown t and rock breaking volume Vrock of rock samples with different heterogeneous H will show obvious fluctuations; among the rock samples with different heterogeneity H, existing a single crack requires a longer breakdown time and the extreme value of the internal conductivity is also significantly larger. And then, the formation of plasma channel is directional selective, extending towards fractures and the weak electrical breakdown intensity. With the dip angle of the fracture increasing, the required breakdown time increases accordingly, and conversely, the broken volume decreases accordingly. The larger porosity of fracture is, the larger broken volume and the shorter required break down time of the rock sample. Furthermore, with the continuous action of electric pulses, multi-fractured rock form interpenetrating plasma channels to improve the rock breaking efficiency. The research results can provide help and theoretical support for optimization of electric pulse rock breaking parameters and the development of electric pulse drilling technology.