Experimental study on stepped discharge modes of cyclic electrohydraulic shockwaves

Abstract

Cyclic electrohydraulic shockwaves drilling technology is expected to solve the problem of rapid drilling in deep and ultra-deep wells. It is expected to improve the rock-breaking efficiency by continuously changing shockwaves under stepped discharge. However, there is still a lack of research on the stepped discharge of cyclic electrohydraulic shockwaves. Therefore, experiments were carried out on eight different discharge modes composed of three voltages of 24, 28, and 32 kV by using self-developed equipment. The results showed that: (1) For modes composed of constant voltage, the higher the voltage, the fewer impact times and electric energy are required to break the rock sample, but it takes longer to break the rock. However, considerable internal cracks only appear after the mechanical strength decreases under a certain number of impacts when the constant discharge voltage is 24 or 28 kV. (2) For stepped modes composed of two or three voltages, such internal cracks appear under the initial impacts, including mode 6, which is composed of 24 and 28 kV. (3) For all the discharge modes, the mechanical strength of rock samples deteriorates linearly with the impact times, and the attenuation rate is also faster under the discharge mode with faster rock breaking speed. In conclusion, the stepped discharge modes can fully combine the advantages of different voltages, and has lower impact times, electric energy, and total time required to break rock samples. Finally, the comprehensive analysis showed that mode 7 (composed of 24, 28, and 32 kV) and mode 6 (composed of 24 and 28 kV) have the best performance in different aspects. In this study, the stepped discharge modes of cyclic electrohydraulic shockwaves were studied in depth, which provides a new idea for the development of this technology and can effectively promote its field application.