The helical buckling and extended reach limit of coiled tubing with initial bending curvature in horizontal wellbores

Abstract

The extended reach limit of coiled tubing (CT) in horizontal wellbores is an important factor restricting the downhole engineering operations of unconventional oil and gas wells. This paper establishes an extended reach limit calculation method of CT with initial bending curvature in a horizontal wellbore. First, this paper assumes that when the initial bending curvature is lower than a certain value, which is called the critical initial bending curvature, the CT will show a sinusoidal buckling configuration when tripping into a horizontal wellbore; otherwise, it will show a helical buckling configuration. Second, based on these two initial configurations, a buckling model and a contact force model are derived. A method of calculating the critical initial bending curvature is also given. Third, a calculation method of the extended reach limit of CT is given on the basis of the buckling and contact force models. The calculation results show that the results from the methodology presented in this paper are consistent with published experimental data. Finally, based on this method, the factors that may affect the extended reach limit of CT are analyzed. The results show that reducing the initial bending curvature or friction factor can effectively increase the extended reach limit of CT. Therefore, the methods presented in this paper can be used to not only predict the extended reach limit of CT but also optimize downhole engineering design parameters.