Effect of Coiled-Tubing Initial Configuration on Buckling Behavior in a Constant-Curvature Hole

Abstract

Summary In practical coiled tubing drilling and completion operations, minor curvature always exists in coiled tubing (CT). The authors ("Effect of Coiled Tubing Initial Configuration on Buckling/ Bending Behavior in Straight Deviated Wells," paper SPE 39003 Presented at the 1997 Fifth Latin American and Caribbean Petroleum Engineering Conference and Exhibition held in Rio de Janeiro, Brazil, 30 August-3 September) previously published that the initial CT configuration results in the reduction of the axial compression force required to produce helical configuration in a deviated well. In this paper, the authors emphasize the effect of initial CT configuration, or residual bending, on buckling behavior in a hole of constant curvature. By utilizing the conservation of energy and the principle of virtual work, new equations are derived to predict the axial compression force for a stable sinusoidal configuration and the axial compression force required to produce a helical configuration. These new equations reduce to those previously published when CT has not been initially bent. Practical examples are presented to demonstrate the effect of the initial amplitude on both sinusoidal and helical buckling behavior of CT in curved wells. The results indicate that the radius of curvature of a borehole is a governing parameter that influences CT buckling behavior. The effect of the initial CT configuration on sinusoidal configuration can be neglected, whereas the effect of the initial CT configuration on helical configuration is substantial. The results will help field engineer to understand CT buckling behavior, and consequently, to select the proper CT to avoid lockup and to improve the prediction of the axial force transmission in horizontal and extended reach drilling.