Experimental and numerical analyses of electro-pulse rock-breaking drilling

The electro-pulse boring (EPB) of deep and ultra-deep wells has great market prospects. It uses controllable energy and is pollution-free. In this paper, research into high-voltage short-pulse power supplies and EPB electrode bits is reviewed. The simulation model was established according to the common coaxial cylindrical structure of the electric pulse rock breaking bit. The effects of the electrode spacing and the shape of the high-voltage electrode on the electric pulse rock breaking were then studied. According to the simulation results, the maximum electrode spacing was determined and the shape of the high-voltage electrode was optimized. The electrode bits with 45- mm spacing and 25-mm spacing were designed. Numerical simulations of EPB using these two bit sizes were conducted in which the actual structure size of the electrode bits and rock physical parameters were used. Simulation revealed an electric field distortion in the rock due to naturally-occurring air gaps, which can enhance the internal electric field strength. An experimental EPB system based on a transformer-type pulse generator was then developed. Transformer oil was used as a drilling fluid and red sandstone was drilled. Electric breakdown of sandstone by 25-mm and 45-mm electrode bits was conducted at a voltage of 80 kV, which produced drilling diameters of 60 mm and 100 mm, respectively. According to the simulation analysis and experimental research of EPB, the effective technological parameters and the law of EPB were obtained, which provided theoretical and practical guidance for electrode bit design and the selection of drilling parameters in practical applications.