Research and Application of Dynamic Anti-Deviation Mechanism of Pre-Bent Drill Assembly in Complex Offshore Formations

During the exploration drilling process, maintaining a vertical well trajectory is a critical issue. In geological formations with complex conditions that are prone to well deviation, conventional drilling tool assemblies exhibit poor anti-deviation performance. To achieve anti-deviation and accelerate drilling in exploration wells, a pre-bent drilling tool assembly is proposed. In this study, a dynamic model of the pre-bent drilling tool assembly was established. The anti-deviation mechanism of the pre-bent drilling tool assembly was investigated. The deviation-reduction effects of the drilling tool assembly under different parameter conditions were analyzed. The results indicate that the deviation-reducing force initially increases and then decreases as the pre-bend angle of the anti-deviation drilling tool increases. When the bend angle is between 1° and 1.13°, a larger deviation-reducing force is generated at the drill bit. A shorter distance (L1) between the near-bit stabilizer and the drill bit, a smaller near-bit stabilizer diameter, and a larger upper stabilizer diameter result in a greater deviation-reducing force. The relationship between the deviation-reducing force and the distance between the two stabilizers (L2) is not explicitly linear, but a decreasing trend is observed after the distance exceeds 10 m. Compared with the conventional pendulum anti-deviation drilling tool assembly, the deviation-reducing force of the pre-bent drilling tool assembly has an advantage of more than two orders of magnitude. Based on the calculation results, the optimal design of the pre-bent drilling tool assembly was carried out. The bend angle was increased to 1.15°, the diameter of the near-bit stabilizer was reduced to 305 mm, L2 was reduced to 9–11 m, and L1 was reduced to 0.9 m. Field applications in 22 exploration wells show that the pre-bent drilling tool assembly provides excellent anti-deviation effects. It can fully release the weight on bit while ensuring a vertical trajectory, achieving a 14% increase in the drilling rate. This technology effectively replaces vertical steering tools. Tool costs are significantly saved, providing an effective method for anti-deviation in complex formations.