Enhancing rock drilling efficiency: Evaluating the effectiveness of ultra-high-pressure water jet slotting technology in granite drilling

Abstract

In response to the issue of increased bottom-hole stress leading to higher rock strength and reduced rate of penetration, a novel drilling technology has been proposed. This technology utilizes ultra-high-pressure water jets to slot peripheral grooves in the bottom-hole rock, reducing stress and enhancing the rock's drillability, which protects the cutter and improves rate of penetration. The purpose of this study is to investigate the effectiveness of this innovative drilling technology and the failure modes of slotted granite during linear cutting, as well as assess the cutting performance of slotted granite. Cutting experiments were conducted to compare both grooved and intact granite in terms of cutting forces, force fluctuations, cuttings size, energy consumed in rock-breaking, the surface morphology along the cutting path, and the micro-morphology of the fracture surfaces. The results indicate that the average cutting force for slotted granite is reduced by 26.57% compared to intact granite, while the fluctuation is increased by 20.06%, increasing the blocky rock masses pronounced. Moreover, the energy consumption of rock breaking for slotted granite is 27.5% lower than that of intact granite. The cutting trajectory of the grooved granite is rougher compared to that of the intact granite, and the fluctuation degree of the cutting trajectory depth has increased by 40.45%, resulting in deeper pits and increased average cutting depth. SEM analysis reveals that slotted granite exhibits more tensile failure on both sides of the cutting trajectory and at the groove fracture surface. The slotted granite reduces the compressive action of confining pressure on the rock and weakens the confining pressure's inhibition on crack propagation. The key findings of this study provide an effective technique for enhancing rate of penetration in hard rock drilling and expand the understanding of rock cutting and breaking mechanisms.