Rock-breaking characteristics and mechanisms of self-rotating self-excited oscillating water jets

Abstract

Hydraulic drilling is an effective technique for the exploitation of deep unconventional oil and gas resources. Enhancing its rock-breaking efficiency and performance is critical for the broader application of this technology. In this study, a novel jet form, self-rotating self-excited oscillating multi-orifice water jets (SSOMWJ), is proposed to impart high-frequency oscillation characteristics to the jet. Comparative rock-breaking experiments were conducted to evaluate performance, with differences in rock-breaking results analyzed through impact force measurements and numerical simulations. The rock-breaking behavior and mechanisms of SSOMWJ were analyzed based on pressure characteristics at the target surface and Computed Tomography (CT) imaging. Results indicate that, compared with conventional self-rotating multi-orifice water jets (SMWJ), the SSOMWJ exhibits superior rock-breaking capabilities and borehole-forming performance. Specifically, rock-breaking volumes increased by 18.73 % and 10.89 %. While drillable depths increased by 75.43 % and 43.85 % at standoff distances of 10 mm and 20 mm, respectively. The SSOMWJ not only generates multiple water hammer pressures but also produces high-frequency stress waves with higher amplitudes during the stagnation pressure stage, in contrast to the SMWJ. The SSOMWJ can utilize these oscillating characteristics to deliver high-energy stress waves and utilize the interaction between the stress waves for improved rock fracturing.