Mechanical Properties Analysis Of Coiled Tubing In Sidetrack Horizontal Well

Slim-hole sidetracking short radius horizontal wells in old wells have good economic benefits.Coiled tubing is widely used in sidetracking horizontal wells.However,the mechanical behavior of coiled tubing in sidetracking horizontal wells is very complex.In order to ensure the safety and economy of coiled tubing application,the mechanical behavior characteristics of coiled tubing must be thoroughly studied.The model of coiled tubing bent around the reel and guide arch,and straightened in the injector chains is established by using finite element software ABAQUS.By using life and death element method,reasonable control of interaction,optimization of the loading and boundary conditions,and regulation of step increments,finally solved the difficulties caused by material nonlinearity,geometric nonlinearity,boundary nonlinearity.The initial residual bending configuration of coiled tubing under wellbore constraints after running into the hole is calculated for the first time.The results show that the initial residual bending configuration is mainly related to the reel radius and the diameter of coiled tubing.The critical buckling load of coiled tubing is obtained by simulating the buckling behavior of coiled tubing in vertical and horizontal wells.The effects of initial residual bending,wall thickness,diameter and boundary conditions on the buckling process of coiled tubing are analyzed.The correctness of the calculation method is verified by comparison of the analytical results of sinusoidal buckling and helical buckling critical loads derived from conventional string theory.The critical buckling load of coiled tubing is greatly reduced due to the existence of initial residual bending of coiled tubing.The deviation of critical buckling load will be large if the results of conventional tubing buckling problem are directly applied to coiled tubing.The residual stress produced by the bending and straightening process of coiled tubing at the wellhead makes the buckling of coiled tubing in downhole an elastic-plastic process.It is an elastic buckling process to study the state of coiled tubing in downhole as a straight tubing state.Therefore,the influence of initial bending must be considered when studying the mechanical behavior of coiled tubing in downhole.The downhole depth of coiled tubing is an important problem in the application of coiled tubing.Taking logging data of a well as an example,the maximum downhole depth considering the residual bending of coiled tubing is calculated.The influence of diameter,wall thickness,drilling pressure and friction coefficient of coiled tubing on downhole depth is analyzed.The larger the drilling pressure,the greater the influence of residual bending on the maximum downhole depth of horizontal section is.The influence of residual bending on well depth can not be neglected.It is suggested that large diameter coiled tubing and high performance drag reducer should be used to increase the depth of penetration,which can be used for reference in engineering application.With the increase of bending and straightening cycles,obvious elliptical deformation and uneven wall thickness thinning occured in coiled tubing under internal pressure.The influence of uneven wall thickness thinning has not been taken into account in previous studies,which leads to higher callapse strength.The effects of diameter,wall thickness,internal pressure and bending radius of large diameter coiled tubing on diameter growth were simulated and analyzed by finite element software ABAQUS.It was found that the elliptical of the cross section and uneven reducation of wall thickness of coiled tubing significantly reduced the extrusion strength of coiled tubing.The inner and outer surfaces of coiled tubing can be approximately characterized as concentric ellipses.The diameter growth of neutral surface is the largest while that of compression and tension surface is relatively small and related to internal pressure.With the increase of cycle times,the wall thickness of compression and tension surface perpendicular to bending axis decreases most,and the wall thickness of neutral surface almost remains unchanged.For the first time,considering the effects of ovality and non-uniform wall thickness reducation,the collapse strength of coiled tubing with different wall thickness varying with the number of cycles under different internal pressures is calculated,which provides a reference for engineering application.