Study on limit passing conditions of one-trip open hole window cutting tool assembly

Aiming at common downhole problems of one-trip open-hole window milling sidetracking tools, including sticking, bending deformation, excessive stress and unstable friction, this paper systematically studies the runnability and drag-torque characteristics of the tool assembly based on a deep test well. Combined with wellbore structure and measured trajectory data, constraint criteria are proposed, and a geometric pass-through model and beam-column bending mechanical model are established. Bending modes are divided into rigid, clearance and deformation types to calculate the ultimate passing curvature and critical dogleg severity. A 3D soft-string model is adopted for full-well drag and torque calculation, and finite element simulation verifies tool strength at the sidetracking point. Results indicate favorable runnability of the tool assembly. The 6–1/2″ drill collar has a critical dogleg severity of 8.94°/30 m, higher than field maximum values. The 3° whipstock leaves adequate safety margin against stress concentration and plastic deformation. Peak drag and torque reach 48 kN and 13,200 N·m, with 1000–3500 m as the high-load interval. This work clarifies safe running limits and proves the technical feasibility, offering references for deep-well open-hole sidetracking.