Underground radial drilling technique is a novel hydraulic stimulation technology, which is one of the important ways to realize precise, intelligent, and efficient extraction of the gas resources. There are many factors influencing the hole‐forming effect by water jet, such as nozzle arrangement and so on. Recently, the self‐rotatory multinozzle drilling bit is frequently used to improve the rock‐breaking effect of water jets. In this paper, to study the effects of inclination angle of forward nozzles and standoff distance, the ANSYS FLUENT combined with RNG turbulence model was adopted to analyze the multinozzle jets flow field. The results indicate that the components of axial velocity and tangential velocity of forward nozzle jets are different with inclination angles of forward nozzles. Moreover, there exists an optimal standoff distance of multinozzle drilling bit for rock breaking. Besides, the drilling test was conducted using the self‐developed drilling simulation system to investigate the effect of inclination angle, radial angle, standoff distance, and jet pressure on the rock‐breaking effect of water jet. Based on the rotating characteristic of rotary jet, the asymmetric inclined linear nozzle arrangement was proposed for the multinozzle drilling bit. And the results also show that the drilling bit with three forward nozzles has larger rock‐breaking zone in terms of jetted hole diameter. Besides, the depth of jetted hole decreased, while the hole diameter increased with the inclination angle of forward nozzle.

With the continuous development of high-pressure water jet technology, research on the optimization of structural parameters for multi-nozzle configurations, the perforation effect of jet rotational impact rock breaking, and the impact force during rock breaking has received increasing attention. Through the development of a self-designed high-pressure water jet rotational drilling test device, rock breaking experiments were conducted on sandstone of different strengths using jet streams with different inclination angles, various combinations of nozzles, different target distances, and different rotational speeds. The parameters and structure of the multi-nozzle jet drill bit were optimized, and the impact of water jet-rock breaking effects was studied. The rationality of different inclination-angle jet streams in rock breaking was verified using the ALE-FEM coupling method. The changes in the force on the target body and the fragmentation mode during rock breaking with different inclination-angle jet streams were analyzed. The results showed that under the condition of adjustable inclination angles, a smaller inclination angle resulted in greater depth and a smaller diameter of rock breaking, while a larger inclination angle resulted in greater width and a smaller depth of rock breaking. The optimal combination of multi-nozzle jet streams was determined to be 20°, 30°, and 60°, which achieved a balance between rock breaking and borehole expansion performance. The efficiency of multi-nozzle jet rotational rock breaking decreased with increasing target distance, with the optimal range being 2 to 4 mm. The rotational speed of the multi-nozzle jet stream had a significant impact on rock-breaking efficiency. Under the same target distance conditions, as the drilling speed increased, the volume of rock breaking initially increased and then decreased, and the rate of volume attenuation increased with increasing target distance. The forms of rock breaking in multi-nozzle jet streams were not identical. Jet streams with smaller inclination angles mainly caused tensile failure through axial impact, while those with larger inclination angles primarily caused shear failure through radial impact. This study provides valuable guidance for optimizing the structural parameters of multi-nozzle jet drill bits and researching rotational rock breaking.