Determination of secondary shoulder clearance of double-shoulder tool joints suitable for extra-deep wells
CHEN Feng, ZHU Wei, DI Qinfeng, WANG Wenchang, CHEN Wei, WANG Nan
(1. School of Mechatronics Engineering and Automation, Shanghai University, Shanghai 200072, China; 2. Shanghai Institute of Applied Mathematics and Mechanics//School of Mechanics and Engineering Science, Shanghai University, Shanghai 200072, China)
In order to meet the requirements of more and more severe drilling conditions, the major drilling tool manufacturers all over the world continuously develop special thread tool joints with premium performance. In general, the structure of secondary shoulder is adopted to form a double-shoulder tool joint. However, it has not been concerned whether the secondary shoulder clearance of the existing tool joints can meet the requirements of the complex working conditions of ultra-deep wells and extra-deep wells. In this paper, a three-dimensional elastoplastic finite element model of a double-shoulder tool joint with different secondary shoulder clearances was established. Then, the influence of secondary shoulder clearance on the stress distribution and torsion performance of tool joints was analyzed. Finally, the secondary shoulder clearance of double-shoulder tool joints suitable for extra-deep wells was determined. And the following research results were obtained. First, under different axial loads (corresponding to different well depths), the secondary shoulder clearance has a great influence on the bearing ratio of primary shoulder, secondary shoulder and thread tooth of double-shoulder tool joints. Second, under the action of large axial force, the bearing capacity of primary shoulder and secondary shoulder are smaller while that of thread tooth is larger, and reducing the secondary shoulder clearance can effectively reduce the bearing ratio of thread tooth. Third, for the NC50 double-shoulder tool joint analyzed in this paper, it is suggested to set the secondary shoulder clearance at 0.40 mm when the axial force is less than 3 000 kN (well depth is less than 9 000 m). Fourth, it is suggested to set the secondary shoulder clearance at 0.20 mm when the axial force is more than 3 000 kN (well depth is over 9 000 m). In conclusion, selecting the double-shoulder tool joint with a rational secondary shoulder clearance according to well depth can effectively improve the application performance of joints and reduce failure risks.
