Optimization Of Flexible Drill Pipe Structure Parameters In Ultra-Short Radius Horizontal Wells

Ultra-short-radius horizontal wells are special wells in which the inclination angle is maintained at about 90° and a certain length of horizontal section is maintained in the target layer.Its main feature is to directly open windows in the casing of the original well.The radius of curvature is particularly small.Not more than 4m.Ultra-short-radius horizontal well technology requires drilling tools with ultra-high deflection ability,but ordinary drilling tools cannot meet this requirement.Therefore,ultra-short-radius horizontal well drilling tools use articulated flexible drill pipes and semi-circular slotted guide screens.The pipe is the main component of the drilling tool to meet the requirements of the drilling process.Under the circumstance that the structure of the guiding screen does not change,in order to make the flexible drilling tool more flexible to achieve deflection drilling,the overall flexibility of the flexible drill pipe needs to be improved.Therefore,the ultra-short radius horizontal well flexible drilling The optimization of rod structure parameters is the key to ensure the high deflection ability of the flexible drilling tool,and it is also the key to achieve the successful drilling of the ultra-short radius horizontal well drilling tool.According to the strength conditions and bending requirements of the flexible drill pipe structure,this paper adopts theoretical analysis methods to analyze the outer diameter of the ball seat on the flexible drill pipe,the maximum outer diameter of the flexible drill pipe,the length of the single section of the flexible drill pipe,and the bending angle of each section.And the five main parameters of the groove length are designed,and the value ranges of the five main parameters are obtained.Taking the single-section flexible drill pipe as the research object,considering the nonlinearity of the contact between the ball head column key and the groove and the material nonlinear characteristics of the flexible drill pipe,the finite element model of the single-section flexible drill pipe is established by the finite element method.The mechanical analysis of flexible drill pipes with different radii of curvature shows that the equivalent stress value at the groove of the flexible drill pipe is the largest,and its value is803.5MPa,which meets the strength requirements and verifies the rationality of the parameterized design of the flexible drill pipe structure.Considering the geometric relationship between the overall flexibility of the flexible drill pipe and the structural dimensions of the flexible drill pipe,the calculation formula for the overall flexibility of the flexible drill pipe is deduced.Based on the response surface optimization method,the strength condition of the flexible drill pipe is established as a constraint.The mathematical model of flexible drill pipe structure optimization with the goal of maximizing the overall flexibility of the flexible drill pipe.The sample points are generated using the best-filled space experimental design method,and the response surface model is fitted by the generated sample points,and the fitted response surface model is optimized by the multi-objective genetic algorithm,and the optimized flexible drill pipe structure size is obtained,The overall flexibility of the optimized flexible drill pipe is 47.1% higher than the original structure.The research results of this paper provide a certain theoretical reference for the structural design of flexible drilling tools for ultra-short-radius horizontal wells.