Research On Strength And Sealing Performance Of Casing Drilling Connection Thread With Torque Ring

Casing drilling technology has been widely used because of its great superiority,but the thread bearing capacity of casing drilling is one of the key factors restricting its development.The torque ring is mounted in the middle of the coupling and increases the torsional strength of the casing drilling threads.In this paper,the BTC thread for casing drilling with torque ring is used as the research object,and its connection strength and sealing performance are studied.Through the analysis of its structure,the make-up torque component is clarified.Based on thick-walled cylinder mechanics,radial and lateral deformation coordination relationship and thread torsional mechanics,Farr formula and contact mechanics,a theoretical calculation model of make-up torque of for casing drilling with torque ring finally is established,which is including radial interference torque,bearing surface friction torque,torque ring shoulder torque.Theoretical calculation shows that the shoulder torque of the torque ring is the main source of the increase of the make-up torque.Based on the theory of threaded connection strength of casing connection recommended by API,the connection strength model under axial force load is established considering the preload of the torque ring shoulder.The connection strength of the 3D model was studied by finite element method,and the stress distribution and deformation characteristics of thread teeth under different loads were analyzed.The results show that the stress concentration level of the last three thread teeth at the small end of the pin under the force is reduced,the mean stress on the bearing surface,the guide surface and the root surface of the middle thread teeth of pin is increased,the strength of the thread connection is enhanced through torque ring.Based on the sealing performance evaluation theory of casing connection thread of API and the traditional leakage rate model,the sealing performance evaluation theory under torque load is established considering the roughness of the shoulder surface of the torque ring.The sealing performance of the 2D model was studied by finite element method,and the stress distribution and deformation characteristics under the make-up torque and different osmotic pressures are analyzed.The results show that the torque ring improves its sealing performance by the contact pressure under load between the shaft end face of torque ring and the small end face of the pin thread.Based on the full-size threaded connection performance experiment and material mechanics test,the BTC thread make-up torque,water pressure test and make-up and down-up test for casing drilling with torque ring with 7 inch steel grade L80-1 are carried out.The results show that the make-up torque calculation theoretical model within the error range of test results is relatively correct,and the make-up torque of the casing drilling thread equipped with the torque ring can be increased from the original 10.84 k N·m to 43.76 k N·m under the premise of ensuring the connection strength and sealing performance.The research work in this paper provides a theoretical basis for the design of the torque ring and the evaluation of the thread connection strength and sealing performance of casing drilling with torque ring,and has certain guiding significance for improving the connection performance of the thread for casing drilling or rotating liner running,and further realizing more economical casing drilling or rotating liner running engineering operations.