Abstract: Coiled tubing (CT), because of the materials which are different from conventional drilling pipe and tube, its operation technique and the facilities, is unique, and fast development of CT has taken place in drilling and production. Meanwhile, the mechanical researche on operating process of CT are also following quickly. Studies on CT, when it is wrapped on the reel, belongs to the area of large elasticplastic stretch bending deformation. By means of general equation of dynamics in the form of virtual work, the torsion torque needed by the reel to wrap CT and the actual output power of hydraulic motor can be derived out. It's found that the torsion torque exerted on the reel is almost linear to the axial stretch of the CT. Mechanical behaviors of CT are analyzed by elasticplastic theory when the CT is wrapped on the reel and then unloaded. It is demonstrated that reversed buckling will not happen. After unloading and resiling, the curvature radius of CT decreases monotonously along with stretch increasing. As a result, stretch is helpful to reducing resilience. It is suggested that the bending moment should also be remained in order to avoid CT resiling and disastrous mess after the CT is wrapped on the reel.

Key words: coiled tubing, reel, elasticplastic stretch bending, unloading, resilience