Numerical simulation of hydraulic optimization of high-pressure electric pulse-mechanical composite drilling bits

Abstract Pulsed electric rock-breaking technology is renowned for its high efficiency and environmental friendliness. However, issues such as borehole wall stability and directional drilling limitations have significantly hindered its widespread application. To address these challenges, this study proposes a novel hybrid drilling method that combines high-voltage pulsed electric drilling with conventional mechanical PDC drilling. A specialized hybrid drill bit was developed accordingly. The hydraulic structure of this bit plays a crucial role in both rock cuttings transport and bottom-hole flow field optimization, which are fundamental to achieving efficient rock fragmentation. Nonetheless, current designs of hybrid bits often overlook hydraulic behavior. To promote the industrial application of high-voltage pulsed-electric hybrid drilling and support environmentally sustainable rock-breaking practices, this study investigates the bottom-hole flow field based on the circulation characteristics of drilling fluid. Two key parameters—residual rock cuttings concentration and retention time—are proposed to evaluate the cuttings transport performance. A hydraulically optimized drill bit was then designed based on these criteria. The results indicate that a larger nozzle azimuth angle intensifies the interference between adjacent streamlines, resulting in a more chaotic central flow field at the bottom hole. Within a suitable range, increasing the nozzle inclination angle enhances cuttings transport efficiency, and the primary flow direction should align with the pressure gradient along the borehole bottom. Additionally, the primary and merged flow directions of the nozzles should avoid obstruction by the grounding electrodes of the pulsed system. Higher flow rates also significantly improve the bit’s ability to carry rock cuttings. These findings provide valuable insights for the design and practical deployment of high-voltage pulsed-electric hybrid drill bits.