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Self-propelled nozzle is a critical component of the radial jet drilling technology. Its backward orifice structure has a crucial influence on the propulsive force and the drilling performance. To improve the working performance of the nozzle, the numerical simulation model is built and verified by the experimental results of propulsive force. Then the theoretical model of the energy efficiency and energy coefficient of the nozzle is built to reveal the influence of the structural parameters on the jet performance of the nozzle. The results show that the energy efficiency and energy coefficient of the backward orifice increase first and then decrease with the angle increases. The energy coefficient of forward orifice is almost constant with the angle increases. With the increase in the number and diameter, energy efficiency and energy coefficient of the forward orifice gradually decrease, but the backward orifice energy coefficient first increases and then decreases. Finally, it is obtained that the nozzle has better jet performance when the angle of backward orifice is 30°, the number of backward orifice is 6, and the value range of diameter is 2–2.2 mm. This study provides a reference for the design of efficiently self-propelled nozzle for radial jet drilling technology. [ABSTRACT FROM AUTHOR]

Due to the increasing depths of coal mines and the low permeability of some coal seams, conventional methods of gas drainage in underground mines are facing many problems. To improve gas extraction, a new technique using water jets to drill tree-type boreholes in coal seams is proposed. A self-propelled water-jet drilling nozzle was designed to drill these boreholes. The configuration of the self-propelled nozzle was optimized by conducting drilling experiments and self-propelling force measurements. Experimental results show that the optimal self-propelled nozzle has a forward orifice axial angle at 25°, a radial angle at 90°, a center distance of 1.5 mm, and backward pointing orifices with an axial angle of 25°. The self-propelling force generated by the jets of the nozzle with 30 MPa pump pressure can reach 29.8 N, enough to pull the hose and the nozzle forward without any external forces. The nozzle can drill at speeds up to 41.5 m/h with pump pressures at 30 MPa. The radial angles of the forward orifices improve the rock breaking performance of the nozzle and, with the correct angle, the rock breaking area of the orifices overlap to produce a connecting hole. The diameter of boreholes drilled by this nozzle can reach 35.2 mm. The nozzle design can be used as the basis for designing other self-propelled nozzles. The drilling experiments demonstrate the feasibility of using the tree-type drilling technique in underground mines.

When coal bed methane (CBM) drainage boreholes cross fractured, soft, or water-swelling strata, they collapse and block frequently. Borehole blockages result in a rapid decrease in CBM extraction ability, which leads to a reduction in CBM output and threatens coal mine safety production. To solve these problems, a novel method that uses a self-propelled water-jet nozzle to dredge blocked boreholes in coal seams has been proposed on the basis of the existing technology. Based on a theoretical analysis of the reason for borehole caving and the theory of blockage removal, we optimized the nozzle inlet pressure and selected an appropriate high-pressure resin pipe. A field experiment on the blockage removal of blocked CBM drainage boreholes using the proposed method was run in the Fengchun coal mine, Qijiang, Chongqing, southwest China. In this field trial, the time spent to unblock a borehole varied between 18.52 and 34.98 min, which is much shorter than using a drilling rig. After blockage removal, the average pure volume of the methane drainage of a single borehole was increased from 0.03 L/min to ~1.91-7.30 L/min, and the methane drainage concentration of a single borehole increased from 5% to ~44%-85%. The extraction effect increased significantly. [ABSTRACT FROM AUTHOR]

Hydraulic radial drilling is an effective technique to increase the production of low-yield oil and gas wells. To improve the operation effect of this technology, a new type of direct-rotating mixed-jet nozzle is proposed, and the drilling performance of the nozzle is studied by combining theoretical, experimental, and numerical simulations. Firstly, the theoretical and numerical simulation models for the drilling performance of the proposed direct-rotating mixed-jet nozzle are established. The experimental results show that the theoretical calculations are in near agreement with the simulations, which verifies the effectiveness of the theoretical and numerical simulation models. Then, the influence of the key parameters on the drilling performance for the proposed direct-rotating mixed-jet nozzle is obtained based on the theoretical and numerical simulation models, and a new type of nozzle structure parameter combination with a better comprehensive performance is derived. Finally, comparing the drilling performance of four different types of nozzle shows that the rock-breaking effect and propulsion performance of the proposed direct-rotating mixed-jet nozzles are better. The research results can provide theoretical support for structural designs and can significantly improve the efficiency of hydraulic radial drilling. • A new type of direct-rotating mixed-jet nozzle structure is proposed in this paper. • The work principle of the new type of direct-rotating mixed-jet nozzle is revealed. • The influence laws of key parameters on the drilling performance of the new nozzle are obtained. • It is indicated that the drilling performance of the new nozzle is better. [ABSTRACT FROM AUTHOR]