| The coal mining in our country is going deeper and deeper,and the gas disaster is becoming more and more serious,which restricts the safety production of coal mine.The technology of surface water jet radial horizontal well is the key problem of gas control.As the key component of the technology,the self-propelled bit can break rock and pull the highpressure hose to achieve self-propelled,which has a decisive influence on the rock-breaking effect and drilling efficiency.However,the self-advancing mechanism of the jet system and the optimum structural parameters of the porous jet bit need further study.In this thesis,theoretical analysis,numerical simulation and experimental research are combined to study the selfpropelled ability of jet system and drill bit structure parameters,it provides a theoretical reference for improving the technology of radial horizontal well and improving the operation efficiency of radial drilling.(1)The simplified model of self-propelled force and the mathematical model of drilling speed are established.Firstly,the backwash force of the water jet from the forward and reverse holes of the self-propelled bit is analyzed theoretically,and the mathematical model of the selfpropelled force of the jet bit is established,and the resistance and suction force of the highpressure hose and the bit under the submerged state are analyzed in detail,on this basis,the mathematical model of the self-propelled force of the jet system is established,the selfpropelled force coefficient is defined,and the mechanism of self-propelled force is revealed.Secondly,the mathematical model of drilling speed of self-propelled bit in coal seam is constructed,the influence of jet flow rate and hole diameter on drilling speed is studied,and the drilling speed of multi-hole bit at different drilling distance in horizontal well is quantitatively analyzed,accurately predict the maximum drilling depth of self-propelled bit.(2)The forward structure parameters of multi-hole jet bit are optimized.Based on Fluent numerical simulation software,the influence factors of jet dynamic characteristics were analyzed by control variable method.The results show that the central nozzles make the jet more uniform,and the annular arrangement with the forward nozzles is more advantageous to rock-breaking and ensure the regular shape of rock-breaking hole The effect of the packing density on the central nozzles is less than that on the lateral nozzles when the packing radius of the packing density is 3.5 mm ～ 4.0 mm,and the optimal ratio of length to diameter of the central nozzles is different from that of the lateral nozzles,the optimum length-diameter ratio ranges from 4 to 4.5.(3)The structure parameters of self-propelled bit are optimized and the experimental research is carried out.The self-propelled force produced by self-propelled bit with different structure parameters is studied by numerical simulation software Fluent.The results show that the jet velocity decreases with the increase of hole number,and the correlation of self-propelled force with the number of forward holes is the largest,confirming that the bit is 1+3+6 type Increasing the diameter of each hole weakens the self-advancing ability of the jet bit,and the self-advancing effect is best when the diameter of the center,forward and backward holes are0.8 mm,0.6 mm,1.0 mm,has the least correlation with self-propulsion.Based on the results of parameter optimization,self-propulsion and rock-breaking experiments were carried out.The results show that the friction resistance in the system makes the measured self-advancing force ratio smaller than the numerical simulation data,the rock-breaking effect becomes better with the increase of erosion time and jet pressure,and the jet distance has an optimal value.This thesis has 66 figures,8 tables and 68 references. |
