Mechanical properties and optimization of deflecting drills with ultra-short radius flexible drill pipes

To improve the drill pipe fracture failure phenomenon in deflecting drills with ultra-short radius flexible drill pipes, this study establishes a mechanical model of a deflecting drill with an ultra-short radius flexible drill pipe, numerically simulates the mechanical characteristics of the flexible drill pipe under the conventional drilling process using the finite element analysis method, performs mechanical performance tests on the flexible drill pipe, and optimizes and improves its structure. The results show that, with the gradual increase in the bending angle of the flexible drill pipe unit section, the upper drilling pressure of the flexible drill pipe unit section decreases rapidly and its friction increases approximately linearly. The tensile strength of the optimized ultra-short radius flexible drill pipe is increased by 24.7%, and the minimum threshold of its torsional strength is doubled. This effectively improves the overall strength of the ultra-short radius flexible drill pipe and provides a theoretical basis for downhole drilling stability studies of flexible drill pipes.