Theoretical and experimental study of buckling behavior of coiled tubing and axial force transfer modeling in coiled tubing drilling

The buckling behavior of coiled tubing (CT) and the axial force transfer modeling in deviated and curved wells are the subjects of this dissertation. In order to attack the problem of buckling behavior of CT, the energy method is applied.;With the assumption that CT is initially non-buckled in deviated and curved wells, equations for predictions of the maximum permissible axial force and the corresponding maximum amplitude for stable sinusoidal configuration are derived. A new equation for the prediction of the least axial compression force required to produce helical configuration in curved wells is also derived.;The effect of CT initial configuration (residual bending) on sinusoidal and helical buckling behaviors has been explored for deviated and curved wells. Using the conservation of energy and the principle of virtual work, new equations are derived for predicting the sinusoidal and helical configurations of CT. Practical examples are presented to show the effect of residual bending on sinusoidal and helical buckling behaviors of CT. The effect of residual bending is important for predicting the axial force transfer, the maximum permissible axial force for sinusoidal configuration, and the least axial force required to produce helical configuration.;This work also presents an improved mathematical model for the axial force calculations while drilling in deviated and curved wells. The new mathematical model is more general as it includes three types of CT configurations: straight, stable sinusoidal, and helical. The equations for predicting the axial force under sinusoidal configuration are believed to be unique for the first time. The sinusoidal configuration of CT is of practical importance as it is a stable configuration for a wide range of axial loads.;The axial force simulator (CTS-TUDRP) has been developed based on the proposed mathematical model. The experimental results conducted at TUDRP horizontal facility are used to verify the proposed mathematical model. CTS-TUDRP can be used to optimize the well path and select proper pipe in practical coiled tubing drilling and completion operations.