Friction-driven buckling evolution and resistance prediction for completion string in complex horizontal well

The downward movement of completion strings in horizontal wells is hindered by geometric constraints and dynamic contact forces, leading to amplified friction and buckling instability, which risk pipe sticking. To ensure safety, suppressing axial buckling propagation is critical. This study establishes a multi-physics coupling model integrating asymmetric contact mechanics and dynamic friction, validated by scaled-down experiments. Simulations reveal a critical stable descent velocity range of 0.1–0.3 m/s; exceeding this limit triggers exponential growth in helical buckling length. A 9.6% nonlinear reduction in hook load at 0.4 m/s indicates energy transfer to buckling deformation. Three-dimensional analysis demonstrates spatial heterogeneity: instability initiates above the kickoff point and propagates upward into the vertical section with increasing velocity and friction, while the horizontal section exhibits sinusoidal buckling. Friction coefficients f 1 (string-casing) and f 2 (string-open hole) synergistically amplify buckling instability. Full vertical-section buckling occurs when f 1 exceeds 0.4 and f 2 exceeds 0.3. Consequently, engineering guidelines suggest restricting f 1 and f 2 to below 0.3 to maintain stable descent. A dual-parameter safety criterion is established to assess buckling risk: (1) the buckling length constitutes less than 30% of the vertical section length; and (2) the buckling-induced contact force accounts for less than 15% of the total contact force. Exceeding either threshold triggers self-reinforcing buckling propagation, culminating in irreversible geometric locking. These findings provide theoretical insights into buckling and friction prediction for completion strings in complex horizontal wells, thereby supporting the optimization of completion designs.