Research And Application Of Dendritic Group Directional Drilling Technology Of In Seam Long Borehole

The directional long borehole in seam can realize advance,zone and precise pre-drainage of coal seam gas,which is an important means of mine gas disaster prevention.At present,the directional borehole in seam is mainly carried out by measuring while drilling.There are some shortcomings,such as unclear control mechanism of drilling track,limited coverage scope of single hole and low gas extraction efficiency,which restrict the hole forming quality and gas extraction effect.Based on the needs of precise trajectory control of directional long borehole in seam and efficient gas extraction,the drilling trajectory control model and lateral branch drilling model were established.The trajectory control characteristics of directional long drilling in coal mine was analyzed,and the branching drilling technology of long drilling in coal mine was studied and formed.The technology has been applied in Sihe and Chengzhuang Coal Mine in Jincheng,and the effect of directional pore-forming and gas extraction is remarkable.The main research work and achievements are as follows:Formation parameters and bit lateral force are the key factors that determine the drilling trajectory.The drilling mechanics model of flat-bottomed directional bit was established,and the influence of anisotropic abnormity and soft and hard interlayer on drilling track deviation of coal measure stratum was analyzed.As the anisotropy coefficient increases,the deviation degree of borehole track becomes stronger.The critical angle range of the interface between soft and hard interbedded formations is generally 10°～20°,beyond which the drilling trajectory will show the trend of top drilling,otherwise it will show the trend of bedding drilling.Based on vertical and horizontal bending method,the suitable mechanical model of trajectory control was established.The calculation method of bit lateral force of screw drill assembly was obtained,and the influence laws of screw drill angle,screw drill angle to bit distance,screw drill equivalent bending stiffness,dip Angle,inclination curvature of drill hole and bit weight on bit lateral force were revealed.The results show that the angle of the screw drilling tool increases,and the lateral force of the bit increases linearly,which is generally set at 1.25°.The distance from the angle of the screw drilling tool to the drill bit increases,and the lateral force of the drill bit decreases obviously.Considering the rationality of the drill structure design,it is generally above lm.The equivalent bending stiffness of the screw drilling tool increases,and the lateral force of the bit increases linearly.The inclined curvature of drilling hole increases,and the bit lateral force decreases rapidly.Drilling angle and bit pressure have little effect on lateral force.The finite element simulation analysis method is used to analyze the bit lateral force of the screw drill assembly,which is consistent with the calculated results of the mechanical model.The reliability of the mechanical model is verified,and the trajectory control accuracy of directional long drilling along the coal seam is improved.Lateral drilling branch is the core technology to ensure long distance drilling in seam and expand drilling coverage area.The mechanical model of lateral drilling branch of near-horizontal long drilling hole was established.It is pointed out that the lateral cutting angle and downward force are the basic conditions of lateral drilling branch.The reservation and selection methods of sidetrack branch points were presented,the principle and applicable formation conditions of low-speed grinding branch method and repeated grinding branch method were analyzed.The dynamic process of sidetrack branch was studied,the key points of drilling in different sidetrack stages were given,and the judgment methods and technical guarantee measures of sidetrack success were summarized.Two kinds of construction technology flow of branch drilling group with forward open branch and backward open branch were developed.The forward open branch was used to ensure the long distance extension of the main hole along the coal seam,and the backward open branch was used to cover the area.The efficient drilling of "one main hole+multi-branch branch hole" in seam was realized,and the gas extraction effect of directional drilling hole was enhanced.Sihe and Chengzhuang Coal Mine in Jincheng were selected to carry out the drilling field test.The new record of 1881m main hole depth of long borehole in Sihe Coal Mine was constructed.In Chengzhuang Coal Mine,77 branch holes were drilled,and the success rate of side branch drilling was 95%.From three aspects of trajectory control characteristics and drilling effect,comprehensive drilling benefit and gas extraction effect,it is proved that the application effect of directional drilling technology of long boreholes in seam is remarkable,which has important theoretical guiding significance and engineering practice value for directional drilling construction of gas extraction in underground coal mine.