The fragmentation mechanism of granite in electrical breakdown process of plasma channel drilling

Abstract

AbstractLow rate of penetration (ROP) and high drilling cost are the key problems that encountered in hot dry rock (HDR) geothermal resources exploitation and utilization. Plasma channel drilling (PCD) is a potential technology which has the advantages of high rock-breaking efficiency and ROP. A detailed understanding of the rock-breaking of PCD is essential to optimize the electrical parameters and bit structure. Therefore, this paper uses the probabilistic evolution model and thermo-mechanical coupling model in PFC2D to reveal the generation of plasma channel trajectory and cracks in heterogeneous granite under the high-voltage electric pulse. The results show that increasing temperature on the plasma channel will not alter the trend of initiation and propagation of cracks, but simply reduces the time consumption of crack initiation. The quantity of intragranular shear cracks is always the largest, and they are mainly distributed around the channel. In addition, compared with plasma channels formed when complete electrical breakdown occurs, the maximum depth of the channels of partial electrical breakdown is larger under the same electrode gap. This study also includes an experimental program to examine the granite fragmentation and borehole generation caused by an electrode bit. The research results can provide new ideas and methods for improving the drilling efficiency of HDR formation, and help to design the structural of drill bits based on PCD technology.