Analysis Of Coiled Tubing Trip-ability In Three-dimensional Bent Wellbores And Improvement Design Of CT Tractor

With the continuous progress of coiled tubing technology,it has been widely used in oil testing,production,fracturing,drilling and grinding,workover and other production links.However,it is difficult to run in coiled tubing,especially in three-dimensional bent wellbores.In serious cases,it needs power traction to run in smoothly.Therefore,it is necessary to analyze the trip-ability of coiled tubing in three-dimensional bent wellbores and improve the design of CT tractor reasonably.Based on the theory of pressure bar stability and mechanical buckling of tubing string,the micro element of coiled tubing is taken for stress analysis,and the differential equations of balance and buckling of coiled tubing are obtained.Based on the special solution method of differential equation and the introduction of dimensionless parameters,the analytical formulas for the critical loads of sinusoidal and spiral buckling of coiled tubing in three-dimensional curved wellbore are established.Based on the theory of elasticity,the equilibrium differential equations of coiled tubing in different well depths are established,and the running friction and friction torque of coiled tubing are obtained.Considering the complex load on the coiled tubing under the condition of drilling and grinding,the shear stress,axial compressive stress and bending stress caused by torque are analyzed.According to the fourth strength theory,the strength safety of the coiled tubing under the condition of drilling and grinding is analyzed,and the safety criterion of the coiled tubing running is established.The key parts and parts that affect the traction performance are simulated and analyzed,and the dynamic traction function of the tractor is simulated,so as to improve the design of the tractor and verify the correctness of the parameter design and the feasibility of the traction.Through the research of this paper,under the condition of ensuring safety,the coiled tubing can be run in smoothly,and the tractor design can be improved to improve the running in performance of coiled tubing under complex working conditions.