Critical helical buckling load assessment of coiled tubing under axial force by use of the explicit finite-element method

Previous theoretical formulations for helical buckling of drill strings vary significantly and are mostly proposed for the linear questions. But there are a little no-linear questions in the mechanical behaviour of tubulars. Explicit finite element analysis (FEA) method has the ability to consider geometric details and nonlinearities. This paper builds an explicit FEA model to describe the behaviors of comprehensive buckling and transmission of axial force for coiled tubing (CT) with residual bending in a horizontal well. The calculational results show that the CT with residual bending is easier to buckle than a straight CT. For the CT with an initial sinusoidal shape, the parameters of initial amplitude and initial pitch are inversely proportional to the helical buckling force, and the outer diameter (OD) is proportional to the helical buckling force. In the process of axial force transmission, the parameters of initial amplitude and frictional coefficient are inversely proportional to the axial force, the OD and initial pitch are proportional to axial force. Residual curvature in coiled tubing appears to have only a small effect on its downhole performance, based on FEA modeling of CT with sinusoidal curvature.