Investigation on rock-breaking and debris transport of high-pressure water jet drilling using the discrete element method (DEM)

Abstract

To address the problems of low drilling efficiency and high cost in deep formation drilling, a new method combining high-pressure water jet and PDC (polycrystalline diamond compact) tools is proposed. However, the rock-breaking and debris transport of composite rock-breaking technology of high-pressure water jets and PDC cutter in jet drilling are still unknown. In this paper, a numerical model of high-pressure water jet and PDC tooth composite rock-breaking is established by the discrete element method and verified with experimental results. Combined with the research results, the rock-breaking mechanism is investigated from the perspectives of crack extension, interfacial friction angle and cutting force. Additionally, the effects of water jet parameters (jet velocity, jet diameter, jet angle, and striking distance) and confining pressure on composite rock-breaking are investigated. Research results show that as jet velocity increases, the impact force on the rock also increases, resulting in greater pit depth and diameter in the impact area, indicating that water jets can cause pre-damage to the rock; The optimal jet parameters are 75° jet angle, 50 m/s jet velocity, 1–1.5 mm jet diameter, and 10–15 mm stand-off distance, which was 10–15 times of the nozzle diameter, respectively; Applying a certain axial confining pressure can improve the efficiency of rock-breaking, and axial confining pressure is easier to load in the range of 0–10 MPa. The above research can provide theoretical support and technical guidance for composite rock-breaking, which is helpful for the improvement of water jet drilling technology and the design of composite drill bits.