A Novel Method for Borehole Blockage Removal and Experimental Study on a Hydraulic Self-Propelled Nozzle in Underground Coal Mines

As the exploration and drilling of oil, natural gas and geothermal wells are expanding continuously, research into high-efficiency rock drilling technology is imperative. High-voltage electro pulse boring (EPB) has the advantages of high rock breaking efficiency and good wall quality, and is a new and efficient potential method of rock breaking. The design of electrode drill bits and the selection of drilling process parameters are the main obstacles restricting the commercialization of EPB. Accordingly, it is necessary to determine the influences on high-voltage EPB. In this study, based on the equivalent circuit of high-voltage electro pulse breakdown, a mathematical model of high-voltage electro pulse discharge in rock is established. Meanwhile, a numerical simulation model of high-voltage EPB of hard granite is established based on a coaxial cylindrical electrode structure, which is often used for electrode drill bits. The simulation analysis software Comsol Multiphysics (Comsol Multiphysics®5.3a, COMSOL Co., Ltd., Stockholm, Sweden) is used to study the influences of granite composition, electrode spacing and electrode shape on the high-voltage EPB process. In addition, the influences of electrical parameters on high-voltage EPB are calculated according to a model of high-voltage electro pulse discharge in rock. Finally, it is demonstrated that high-voltage EPB is influenced by granite composition, electrical parameters, electrode spacing, and electrode shape, and the relationships between these factors are obtained. This study is of guiding significance for improving rock breaking efficiency, reducing energy loss, designing electrode drill bits and selecting drilling process parameters.

Section: Introductionmentioning

confidence: 99%

Influences on High-Voltage Electro Pulse Boring in Granite

Duan

Tan

et al. 2018

“…To control the high mining pressure occurring in the overlying structures, hydraulic fracturing and blasting has been developed to deal with the stress concentration based on weakening the hard roof [5,[10][11][12][13][14]. Hydraulic fracturing is achieved by using fracturing equipment and high pressure water [12]; the blasting is done by placing an explosive in the borehole [14].…”

Section: Introductionmentioning

confidence: 99%

Reduction of Stress Acting on a Thick, Deep Coal Seam by Protective-Seam Mining

Gao

Xia

et al. 2017

Aiming to reduce the high mining stress observed in large-space roof structures during mechanized mining of thick coal seams, a control technique based on protective-seam mining is proposed. This technique was used to investigate the 8108 working face of the No. 3-5 thick coal seam of the Tashan mine located in the Datong area of Shanxi, China, by means of simulations and field measurements. The numerical simulation revealed that the No. 3-5 coal seam undergoes expansion and deformation, accompanied by stress relief due to the mining of the overlying No. 4 coal seam. The physical simulation demonstrated that mining the protective seam changes the structural characteristics of the overlying strata in advance and reduces the integrity of the roof in the No. 3-5 coal seam. Field measurements showed that the support loads in the 8108 working face are significantly weaker than those in the adjacent 8107 working face, where protective-seam mining was not performed. In the absence of high resistance on the support and distinct periodic weighting characteristics, the rock masses around the 8108 working face and roadway could be easily supported.

“…As a result, the penetration rate was improved ranging from 10.1 to 31.5%. Ge et al [2] proposed a novel method that used a self-propelled water-jet nozzle to dredge blocked boreholes in coal seams in order to improve the coal bed methane output and coal mine safety. The nozzle inlet pressure was optimized and a field experiment on the blockage removal of blocked coal bed methane drainage boreholes using the proposed method was conducted.…”

Section: Introductionmentioning

confidence: 99%

Large Eddy Simulation of Self-Excited Oscillation Pulsed Jet (SEOPJ) Induced by a Helmholtz Oscillator in Underground Mining

Fang

Zhang

et al. 2019

Pulsed waterjet can break rocks effectively by taking advantage of the water hammer effect, and is thus widely used in mining, petroleum, and natural gas fields. With the aim to further clarify the flow field characteristics of pulsed jets induced by a Helmholtz oscillator, large eddy simulation was conducted under different operating pressures. The velocity distribution, mean flow field, and the coherent structure were examined using the oscillators of different cavity lengths and diameters. The results clearly showed that the major frequency of jet pulsation gradually increased with the increase of operating pressure. A stable periodic velocity core was formed at the outlet of the Helmholtz oscillator, while the external flow field was subjected to periodic impact. As a result, the ambient fluid was strongly entrained into the jet beam. With the increase of the cavity length, the length of the core segment decreased while the energy loss caused by the cavity increased, which was also accompanied by a rapid attenuation of the axial velocity at the jet outlet. The coherent structure of the jet in the oscillator with small cavity diameter was more disordered near the nozzle outlet, and the vortex scale was larger. The effect of cavity diameter can be reflected in the feedback modulation of the jet in the cavity. Compared with the conical nozzle, the length of the core section of the jet was shorter, but the jet had better bunching, a smaller diffusion angle, and better mixing performance. These results provide a further understanding of the characteristics of pulsed water jet for better utilizations in the fields of energy exploitation. a self-propelled water-jet drilling nozzle to drill three-type boreholes to improve gas extraction and drilling experiments were conducted to optimize the nozzle configuration. As a generator of SEOPJ, attention has been paid to the Helmholtz oscillator and extensive research has been done by . The unsteady flow phenomenon in SEOPJ is combined with various theories such as fluid dynamics, fluid resonance, and hydroelasticity, which makes it difficult to measure the flow patterns and vortex structures. In particular, an experimental study was conducted to characterize the discrete model by the change of cavity length and to give stable working regions under various parameters [7]. The identification of the complex mechanism responsible for this phenomenon is difficult because it is the result of multiple factors and data acquisition of all the instantaneous fields simultaneously is unavailable under the existing measurement techniques [8].Energies 2019, 12, x FOR PEER REVIEW 3 of 21 be distinguished. The research results can be used as the theoretical basis for selection and design of SEOPJ nozzles in underground mining.