Abstract

In practical coiled tubing drilling and completion operations minor curvature always exists in coiled tubing (CT). The authors previously published that CT initial configuration results in the momentous reduction of the axial compression force required to produce helical configuration in a deviated well. In this paper the authors emphasize the effect of CT initial configuration on buckling/bending 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 maximum permissible axial compression force to maintain a stable sinusoidal configuration and the axial compression force required to produce a helical configuration in a hole of constant curvature. These new equations reduce to those previously published when CT is not initially buckled. Practical examples are granted 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 to influence CT buckling/bending behavior in a curved well. The effect of CT initial configuration on sinusoidal configuration can be neglected, whereas the effect of CT initial configuration on helical configuration is substantial. The results will help field engineer to understand CT buckling behaviors better, and consequently, to select proper CT to avoid the occurrence of lockup and to improve the prediction of the axial force transmission in horizontal and extended reach drilling. All equations manifested here can also be employed to conventional rotary drilling, slime hole drilling and tubular design.

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