| When the downhole water jet is used to cut coal,the water slag is discharged slowly and the borehole is filled with flowing water slag,so it is a typical submerged water jet.Under the influence of water cushion effect and pressure holding effect,the effect of breaking coal is not good.Secondly,the accumulation of water and slag debris in downhole will block the passage of gas flowing in the coal seam and block the gas drainage pipeline,which will seriously affect the effect of gas drainage.In order to improve the efficiency of downhole coal breaking,in view of the problems existing in the process of coal breaking and gas extraction,the thesis studies the optimization of water jet nozzle and the technical equipment of drainage and slag discharge during the extraction.On the basis of theoretical analysis,it is proposed that the self-excited Oscillation pulsed jet nozzle enhanced by annulus fluid is used to modulate the pulsed jet to eliminate the water cushion effect and the pressure holding effect.The L16（45）orthogonal table with four factors and four levels was used to design the simulation scheme,and the large eddy simulation（LES）was used to optimize the structural parameters such as the diameter of the lower nozzle d2,the cavity length l and the cavity diameter D of the resonator,and the diameter of the leading-in nozzle d3.Based on the large Eddy Simulation（LES）results,the effects of various parameters on the jet characteristics were analyzed,and the optimum values of each parameter were determined by range analysis method.In order to investigate the performance of the optimized annular fluid-enhanced self-excited Oscillation pulsed jet nozzle,a comprehensive testing platform for hydraulic antireflection technology was developed,and the performance of the self-excited oscillation pulsed jet nozzle enhanced by annulus fluid was analyzed.Compared with the common nozzle,the average striking force of the self-excited pulsed water jet in the submerged condition is almost the same,and the maximum striking force is more than twice.When the pump pressure is 10MPa and the target distance is 11d1or 33mm,the jet has the best erosion effect on coal sample,the depth of erosion is 47.32mm,the volume of erosion is 15.7 cm3.In order to solve the problems of water and slag accumulation and poor effect of gas drainage in downward boreholes,based on step-by-step transportation mode of"water injection slag,pressure air drainage"way,a transportation mechanism of high-efficient circulating water and slag drainage in downhole drilling was put forward,in this thesis.An integrative equipment of downhole drainage and slag extraction is designed,and field test is carried out in Yian Coal Mine.The results show that the cuttings with size 8 mm or less can be discharged effectively.The drainage operation can be completed in 10 min without external water supply.After the drainage and slag discharge operation,the concentration of single boreholes is increased from 0%to60%～85%.When there is additional water source in the borehole,the time of high efficient extraction can be prolonged by using irregular drainage and slag discharge.A long examination of the effects shows that the gas drainage concentration is increased by 2.8～12.6 times.Studies have shown that,the equipment can effectively discharge the water slag accumulated at the bottom of the borehole and the fissure water flowing into the borehole in the process of extraction,and can realize the rapid switching and circulation operation of three working states of slag discharge,water discharge and gas drainage,improve the pumping efficiency of the downhole drilling,it provides technical guarantee for hydraulic anti-permeability technology of down-hole and high-efficiency gas extraction. |
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