Research on the Design of Mid-Section Thickened Elongated Drill Pipes

Elongated drill pipes offer significant advantages, including reduced threaded connection time, lower frictional torque, and minimized circulation pressure loss. However, their extended length increases the risk of mid-section contact with wellbore walls, leading to accelerated wear and reduced service life. To address this challenge, this study proposes a mid-section thickened elongated drill pipe design. A comprehensive multi-body dynamics model of the full-well system was developed, and simulation experiments were conducted using an experimental well with controlled dogleg severity variations in the build-up section. These experiments evaluated both externally thickened and internally thickened designs to determine the optimal mid-section thickening parameters. Following parameter optimization, the variation of contact forces between the mid-section of the drill pipe and the wellbore wall was analyzed as a function of dogleg severity. A comparative study was performed to assess differences in contact forces, axial forces, torque, bending moments, and stress distribution between mid-section thickened elongated drill pipes and conventional elongated drill pipes. The effectiveness of the thickened design was further validated through simulations in three operational scenarios: vertical deep wells, horizontal wells, and complex structural wells. Key findings demonstrate that increasing the mid-section thickness of elongated drill pipes enhances their tensile-compressive resistance, bending resistance, and structural integrity. This design significantly reduces bending deformation, mitigates stress concentration, and decreases mid-section contact forces with the wellbore. Consequently, the thickened configuration enables the deployment of longer drill pipes while maintaining operational reliability and extending service life. The results provide critical insights for optimizing drill pipe design in challenging drilling environments, particularly in applications requiring extended reach or complex well trajectories.