Study On Precise Directional Drilling Technology For Gas Drainage Boreholes

Gas drainage is the main measure to reduce the amount of gas discharged by mine wind and prevent gas disasters.At present,there is a common problem of serious deviation of boreholes in gas drainage.The deviation of the boreholes causes the pre-drainage holes to deviate from the design position,and even some boreholes deviate greatly,resulting in blank drainage zones,thus affecting the gas drainage effect.In order to solve the serious deflection problem of coal mine gas drainage boreholes,the precise directional drilling tool was developed and improved and its effect was verified,and the general laws of borehole deflection was summarized.The research results have important reference significance for preventing gas drainage borehole deflection and further research on precise directional drilling tools.This paper combined the methods of theoretical analysis,numerical simulation and field experiments to conduct the following studies:(1)By analyzing the three main factors that lead to the deflection of the drilling hole:geological factors,technical factors and construction factors;the force analysis of the drilling pipe in the hole was carried out,and the three conditions for the deflection of the drilling hole were summarized: mechanical conditions,Space conditions,location conditions.(2)The stress and displacement changed in different directions in isotropic coal seams and anisotropic coal seams before and after using the precise directional device were studied by ANSYS numerical simulation.The results showed that the stress and displacement changed at the drill bit were significantly reduced after the installation of the precise directional device.(3)The reasons for the deflection of the borehole were analyzed,the passive deflection correction technology of the borehole was studied,and finally the full-hole drilling technology was decided to adopt.Combined with the three-edged drill pipe and the grooved drill pipe,a six-edged fancy grooved drill pipe was innovatively designed,and a reverse drill bit and a three-edged short pipe were installed at the tail to ensure full-hole drilling,smooth slag discharge,and smooth drilling.Considering the parameters of coal mine drilling tools and labor intensity of workers,the specific parameters of precise directional drilling were finally determined.(4)By using ordinary drilling pipe,and one to three sets of precise directional drilling tools,16 test boreholes were drilled.The inclinometer was used to collect the parameters of the borehole measuring point in the way of one measuring point of 1m,and the coordinates of each measuring point of the borehole were obtained by processing the data by the average angle method.Then the origin software was used to draw comparison charts between the actual trajectory and the theoretical trajectory of the boreholes.(5)The results showed that the inclination angle of the boreholes generally first tended to decrease and then to increase,and the change of the boreholes azimuth basically increased.Taking every 25 m as a depth interval,the inclination deviation and azimuth deviation of the boreholes were the largest in the range of 50-75 m.And the precise directional drilling tool was very effective in reducing drilling deviation.Combined with the slag discharge effect and the time-consuming of drilling withdrawal,using two sets of precise directional drills had the best comprehensive effect.The average change of inclination angle was reduced by 81.5%,the average change of azimuth angle was reduced by 55.7%;the average of final hole deviation was reduced by 61.0%,and the average of final hole deviation per 100 meters was reduced by 64.0%.There are 23 figures,15 tables,and 86 references.