Research on rock-breaking instability characteristics and spin deflection effects of asymmetric water jet impact

Abstract

The asymmetric nozzle arrangement can further reduce the size of the water jet drill bit, enhancing its suitability for confined downhole spaces while simultaneously improving rock-breaking efficiency. Existing self-rotating water jet drill bits predominantly utilize combined nozzle arrangements, yet systematic investigations into asymmetric configurations remain limited. Building upon the theory of high-pressure water jet impact dynamics and the spherical cavity expansion model, this study establishes a rock-breaking model for asymmetric water jets, revealing the instability characteristics of rock failure induced by asymmetric water jet impacts. An optimized asymmetric nozzle arrangement was designed, with Fluent simulations employed to determine the optimal nozzle combination for rock fragmentation. Rotational flow field experiments of asymmetric water jets were conducted, and MATLAB-based numerical processing was implemented to validate the rotational-speed-dependent variations in the flow field. Key findings demonstrate that under identical nozzle quantities, asymmetric water jet impacts exhibit more pronounced rock failure instability characteristics along with enhanced rock-breaking width. The optimized angular configuration was identified as 20° (first nozzle), 30° (second nozzle), and 60° (third nozzle). Notably, a significant rotational deviation effect emerges during asymmetric water jet rotation. Both experimental and numerical analyses suggest that beyond 800 rpm, the rotational deviation effect saturates concurrently with intensified water jet atomization. Therefore, rotational speed regulation is critical to prevent rock-breaking efficiency degradation caused by excessive velocities.