Analysis of Running Ability for Coiled Tubing in Horizontal Wells

Abstract

Due to the large slenderness ratio and low bending stiffness of coiled tubing, it is prone to buckling and self-locking during operations in complex and long horizontal wells, thus failing to reach the target depth. To address this issue, a full-hole mechanical model for coiled tubing running is established in this paper, taking into account multiple factors including contact friction between coiled tubing and casing, fluid resistance inside and outside the tubing, and annular fluid lift force on the tubing. The influences of friction coefficient, residual initial stress and build-up rate on axial force, CT buckling and friction during running are investigated. The results show that a high friction coefficient increases the friction growth rate in the build-up section by 2–3 times and advances the tension-compression transition point by 430 m; a tensile residual stress of 50 MPa advances the neutral point by 131.7 m, while a compressive residual stress of −50 MPa delays compression by 156.57 m and reduces friction; a high build-up rate of 8°/30 m advances the neutral point by approximately 300 m and increases the peak friction by 90%.