| Coal mine gas disasters in our country are very serious,and the large area pre-drainage of coal seam gas is a fundamental measure to prevent gas accidents.The soft coal seam is affected by multiple factors,such as in-situ stress,hardness of coal seam,gas content,etc.,therefore the borehole wall instability and deformation process is complicated,and the amount of produced slag is large.The commonly used drilling technology is difficult to discharge slag in time and effectively.During the drilling process,there are series of phenomena such as hole blockage,stuck drill,and holding drill,which lead to the drilling depth not meeting the engineering requirements.Therefore,research on the related technology of slagging in soft coal seams to improve the efficiency of drilling slag and improve the gas in soft coal seams.The extraction efficiency is of great significance to ensure the safety of coal mining.This thesis aims at the technical difficulties of slagging in the process of drilling in soft coal seams.It mainly combines the advantages of reverse circulation slagging technology and spiral blade slagging technology,and adopts theoretical research,numerical simulation,laboratory experiments and other methods to analyze the soft coal seams.The kinetic mechanism of channel reverse circulation slag discharge have been studied,and the thesis mainly includes the following aspects:(1)Analyzing the working principle and characteristics of the spiral slag discharge,compressed air slag discharge and three-channel reverse circulation slag discharge,and establish a dynamic characteristic model based on the hydrodynamic energy equation,isentropic flow equation and The gas equation of state,etc.,deduced the dynamic equation of state for three slagging methods,and revealed the quantitative influence mechanism between the three-channel reverse circulation slagging capacity and the influencing parameters.(2)Designed and constructed a three-channel reverse circulation drilling tool slag discharge performance simulation experimental device,which can reflect the reaction of different bottom nozzle diameter,ejector hole diameter,ejector hole inclination,and number of ejector holes under different inlet flow conditions.Simulation experiments were carried out on the suction flow rate and suction negative pressure changes in the circulating drilling tool,and it was found that the bottom nozzle diameter is 3mm,the ejection hole diameter is 4mm,and the ejection angle is 20°.The channel reverse circulation drilling tool has the best slag discharge performance.The maximum suction flow of the center channel is 98.9m3/h,and the maximum suction negative pressure is-8.1kPa;when the best structural parameter combination,the three-channel reverse circulation drilling tool starts to work The minimum inlet air volume of the DR is 147m3/h.With the increase of the inlet flow,the suction flow of the central channel in the reverse circulation drilling tool system increases linearly with the inlet flow,while the outer annulus flow remains basically unchanged,and when the reverse circulation The larger the particle size of the medium,the higher the specific gravity,and the smaller the gas-solid ratio,the lower the slag discharge rate.(3)Using the k-ε turbulence model of Fluent software,the three-channel reverse circulation drilling tool is separately tested under different bottom nozzle diameters,ejector hole diameters,ejector hole inclination,and number of ejector holes under different air volume conditions.The flow velocity field distribution,pressure field distribution and suction coefficient in the three-channel reverse circulation drilling tool system are simulated.The simulation results show that the greater the inlet air volume,the greater the flow velocity and pressure in the three-channel reverse circulation drilling tool,and the bottom spray The single-row six-hole reverse circulation drilling tool with a hole diameter of 3mm,an ejector hole diameter of 4mm and an ejection angle of 20° has the best slag discharge performance.When the inlet flow rate is 4m3/min and 8m3/min,the reverse circulation The maximum flow velocity and negative pressure in the drilling tool system are 199m/s,13.6kPa and 439m/s,39.0kPa,respectively;the maximum flow velocity and negative pressure in the reverse circulation drilling tool are located near the exit of the central channel;the reverse circulation drilling tool The flow velocity and negative pressure in the axial direction of the central channel both increase first and then decrease,and the maximum value appears at a certain position away from the outlet of the nozzle;with the increase of the inlet air volume,the pumping of the reverse circulation drilling tool system Instead,the suction coefficient decreases.(4)Based on the theory of stress and strain reconstruction in the process of drilling in soft coal seams,according to the linear Mohr-Coulomb yield criterion and the plastic flow rule,the full pressure relief zone(broken zone)and the insufficient pressure relief zone(Plastic deformation zone)distribution radius and drilling radius change with time,revealing the deformation and slag generation mechanism of drilling in soft coal seams;through engineering statistical analysis methods,the actual slag production and drilling depth,coal seam depth,Single factor and multi-factor quantitative influence function relationship of gas content and coal seam firmness coefficient.(5)Based on the previous research results,the structural parameters of the three-channel reverse circulation drilling tool ejector are determined,and the three-channel reverse circulation drilling tool is designed through calculation and verification of the structure size and strength of the three-channel reverse circulation drilling tool.The structural parameters are:the diameter of the central channel is 40mm,the inner diameter of the annulus is 71mm,the outer diameter of the annulus is 89mm,and the spiral outer diameter is 133mm.The ejector bottom adopts a single-row six-hole uniform arrangement,and the nozzle diameter is 3mm.The diameter of the perforation hole is 4mm,and the inclination angle of the perforation hole is 20°;the designed three-channel reverse circulation drilling tool has spiral slag discharge,compressed air slag discharge and reverse circulation central channel slag discharge capacity of 0.71kg/s、0.431kg/s and 0.94kg/s,respectively.The total designed slag discharge capacity is 2.08kg/s,which can completely discharge the slag produced by drilling holes in soft coal seams above 200m.Figure[100]Table[10]References[172]... |
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