Ultra Short Radius Steering Mechanism Research Of Seam Branch Hole Hydraulic Drilling

The effective drainage of coal seam gas has great significance for safe and efficient coalmining. To improve the rate of gas drainage, using radial horizontal drilling technologyapplied in the coal seam pressure-relief main hole to drill multiple horizontal branch holes is aprospective method. According to the restricted space and bad working conditions ofpressure-relief main hole, the branch holes drilling assembly was designed which include toolhousing, guiding unit and drilling unit.Drilling pipe is the key components which assisted drilling bit complete steering to drillbranch holes. To define drilling pipe parameters, experiment on the match of drilling pipewith steering track was conducted, during which four drilling pipes different in outer diameter,wall thickness and material were tested and the influence of these parameters on steeringresistance was studied. The experiment shows that under the same conditions, small outerdiameter means smaller steering resistance; small wall thickness means smaller steeringresistance; small plastic limit means smaller guide resistance. As for drilling pipe material,stainless pipe is selected and theoretical calculations combined with experimental method wasused to check the resistance to internal pressure.Take advantage of theoretical calculations, the factors affect guide unit steeringresistance was analyzed, found that turning radius and straightening offset has great influenceon steering resistance, under which preliminary designed steering track. In order to reduce thesteering resistance, the process of drilling pipe go through steering track was numericalsimulated and the stress distribution of drill pipe was observed. By analysis the variation ofresistance and feed distance, found that steering resistance increased where track curvaturechange, and shows a positive correlation with the amount of curvature change. Based on thisdiscover, optimized steering track shape, numerical simulations showed that steeringresistance is reduced by17%after optimization.Nonlinear numerical simulation was used to analysis the drilling pipe bucklingphenomenon, the simulation shows that drilling pipe in righting barrel is sinusoidal buckling,and become invalid due to plastic yielding. Based on the simulation, analysis indicated that under same conditions, the greater the length of drilling pipe, the greater the maximum axialforce; the larger inner diameter of righting barrel, the smaller the maximum axial force.According to this, combined with steering resistance defined geometry parameters of guideunit.