Nonlinear Buckling Analysis and Ultimate Extended Capacity Research of Downhole Pipe Strings in Ultra-Deep Horizontal Wells

Abstract

The downhole operation pipe strings in ultra-deep horizontal well is a super-thin elastic beam. Its running process is constrained by the 3D curved wellbore. The buckling deformation was occurred when the concentrated force and the internal and external walls liquid pressure exert on the operation pipe strings. The ultimate extended capacity of operation pipe strings was determined by critical buckling condition. In this paper, based on a continuous contact hypothesis of the pipe strings and borehole wall in large deviation hole section, the nonlinear buckling equation was improved. The critical load of pipe strings was obtained under different wellbore condition and the ultimate extended capacity of operation pipe strings was evaluated. Moreover, the concentrated force at the top-end of pipe strings was determined by the iterative fitting method. It is found that the ultimate extended capacity of downhole operation pipe is not determined by friction force but also determined by the buckling critical load