Dynamic Model of Pipeline Pullback Loads in Horizontal Directional Drilling

Pipeline pullback loads in horizontal directional drilling (HDD) are critical for drill rig selection and pipe strength design. Current calculation methods are predominantly static, making it challenging to fully consider pipe's motion and deformation. To address this, we introduce the absolute nodal coordinate formulation (ANCF) for dynamic modeling. A pipe–borehole wall contact detection strategy is proposed based on global coordinates and the minimal distance criterion. The system's dynamic equations are then established together with a dedicated numerical solution scheme. The model is validated against field measurements from a 176‑m HDD crossing, yielding an average relative error of 5.8% in peak pullback loads. Compared with existing dynamic models, the proposed framework incorporates drilling fluid drag force and a velocity‑dependent continuous friction model, thereby extending applicability and enabling the simulation of stick‑slip motion and periodic contact–separation phenomena. Moreover, the computational approach requires neither borehole discretization nor empirical contact stiffness, thereby improving the objectivity of the results. The model identifies local axial force elevations at the transition points between curved and straight segments, providing guidance for targeted pipe strength design. Furthermore, by quantifying the effects of different buoyancy control methods on the axial force distribution, it provides a quantitative basis for selecting the safest strategy tailored to specific locations along the pipeline. The proposed framework thus offers a comprehensive tool for drill rig selection, pipe strength design, and construction optimization under complex field conditions.