Mechanical Analysis Of Coiled Tubing For Drilling

Along with the development of coiled tubing (CT) technique and drilling technique, coiled tubing drilling (CTD) has become an important technique in resent years. It is very important for exploration and exploitation to research & develop CT technology. CT Buckling, axial force transfer, mechanical property and fatigue life are studied in the paper. It covers the following contents.(1) Using energy method, equations are derived to predict the axial compression force required to produce buckling in vertical, inclined, and curved wells. Utilizing the Lagrange multiplier method, the unit lateral contact force corresponding to straight, sinusoidal, and helical configurations between CT and casing are obtained in vertical, inclined, and curved wells, respectively. The buckling of CT is also discussed on the basis of ABAQUS computer simulations.(2) Taking the buckling of CT into account, the axial force transfer characteristics is analyzed in vertical, inclined, and curved wells, respectively. CT axial force transfer model is obtained.(3) Mechanical behavior of CT is studied. The model of bending, internal Pressure strength and external collapse pressure, Diametral Growth and stuck-Point of CT is established. Numerical analysis is done for CT collapse pressure by ABAQUS FEM software. Results show that CT will bring alternative bending plastic deformation. The larger the ovality is, the smaller the collapse resistance.After working repeatedly under certain internal Pressure,the diameter of CT will increase and wall thickness of CT will become smaller. Longitudinal stretch of CT will happen during shift, which will bring additional force.(4) A model of CT working fatigue life is presented. The factors affecting CT fatigue life are analyzed(sensitivity analysis) and the methods of improving the CT life are given. Internal pressure, CT OD, CT wall thickness, reel diameter, gooseneck radius, Young's modulus and working medium affect CT fatigue life severely. Increasing the diameters of the reel and gooseneck as much as possible, increasing the wall thickness of large-diameter CT, and selecting small-diameter CT firstly can improve the fatigue life.