Determination of Makeup Torque and Secondary Shoulder Gap of Drillstring Connection Based on 3D Model

Summary The safe and efficient extraction of deep oil and gas resources demands improved well construction techniques. Frequent failures of drillstrings with industry standard American Petroleum Institute (API) rotary-shouldered connections (RSC) have been reported, and adopting double-shoulder connections (DSC) can significantly reduce such failures. Currently, there is a lack of precise methods for calculating the makeup torque of DSC, which affects the joint size design. To address this issue, a 3D finite element model of various types of connections is developed to simulate the screw-in process, analyze the average axial stress in critical sections under applied torque, and determine the appropriate makeup torque according to API standards. The method’s effectiveness is validated through application to the NC38 joint. Unlike analytical solutions, this study provides a more accurate assessment of the average stress in the section. Additionally, for DSC, the secondary shoulder gap can be optimized during the makeup torque determination. The optimal gap should ensure that the torque ratio of the secondary shoulder after assembly remains between 8% and 10%. The joint with the optimized gap was then subjected to a torsion test. The shoulder was firmly joined, with no material loss due to overfitting at the thread contact surface. This workflow offers a cost-effective method applicable to existing drillstring threaded connections and new designs, aiding in determining the length of pin and box, manufacturing deviations, and providing operational parameter guidance for field applications.