Research On The Mechanical Properties Of Special Threaded Tubing Joints Under High Temperature And High Pressure

With the continuous development of oil extraction technology,high temperature wells(bottom temperature above 150 ℃),high pressure wells(bottom pressure greater than 70 MPa or wellhead closed pressure greater than 35 MPa)and deep wells(greater than 5000 m)are widely developed.The use environment of the downhole string is deteriorating,and frequent failures of the tubing joints have imposed stricter requirements on the connection strength and sealing performance of the joint.Tubing joints are more complex during operation and are typical nonlinear problems.Scholars mostly use two-dimensional axisymmetric models when researching tubing joints,and a few use three-dimensional mechanical models,and there are few researches and analysis on three-dimensional mechanical properties of joints with complex structures.In order to solve the above problems and ensure the safety reliability of the tubing joint in the downhole operation,this paper designs a premium threaded tubing joint with a two-stage main seal and shoulder auxiliary seal structure,which belongs to the three-stage metal seal form.The finite element software analyzes the joint strength and sealing performance of the joint under different tightening torques.After the optimal torque is tightened,the temperature of the joint under different axial tensile,compression,external pressure,internal pressure and bending conditions is studied.The effect of the loads on its mechanical properties.The specific content of the research and results achieved are as follows:(1)Based on the research status of sealing mechanism,connection theory,finite element method and test method of special thread of oil pipe at home and abroad,the problems existing in the research field of tubing joint are analyzed,and the research ideas and main contents are put forward.(2)A special threaded oil pipe joint with two-stage main seal and shoulder auxiliary seal structure is designed.Considering the mechanical properties of the joint is affected by the angle of the thread,based on the theory of nonlinear mechanics and Miss yield criterion,the joint is established.3D computing model.(3)The stress state of the joint after the different torque is buckled is analyzed.Considering the effect of the joint stress on the temperature change,the influence of temperature on the mechanical properties is studied.The results show that after the three kinds of torque buckles are used,significant stress concentration occurs in the shoulder,cylinder and cone seals.The maximum Miss stress occurs when the maximum buckle torque is applied.When the minimum torque is used,the table is tightened.The shoulder seal is poor;the temperature has little effect on the maximum Mises stress of each thread and the contact stress of the shoulder,cylinder and cone sealing surface;as the temperature increases,the stress of the shoulder increases first and then decreases,while the cylinder and the stress of the tapered surface gradually decreases.(4)Analyze the stress state of the joint under tension,compression,internal pressure,external pressure and bending load respectively,and the temperature load on the joint under tension,compression,internal pressure,external pressure and bending load The effect of joint strength and sealing performance.The results show that with the increase of temperature load,it is concluded that the temperature variation between 220℃ and 320℃ has a great influence on the joint stress characteristics.(5)The joint strength and sealing performance of the joint under tensile and internal pressure+bending and compression+internal pressure+bending were analyzed.The results show that the last two teeth of the two composite loads are concentrated and Miss.The stress is greater than the yield limit of the material,but the whole segment of the thread is connected reliably;under the tensile+ internal pressure+bending composite load,the tensile end of the shoulder is prone to seal failure;under compression+internal pressure+bending composite load,the table Shoulder and cylinder stress values are higher.(6)The effect of temperature on joint strength and sealing performance of joints under two composite loads was investigated.Under the action of two kinds of composite loads,the maximum contact stress of the sealing contact surface changes uniformly.The sensitivity of the three sealing structures to temperature changes,from large to small,is:cone>shoulder>cylinder.With the increase of temperature load,it is concluded that the temperature change has a great influence on the joint stress characteristics from 20℃ to 120℃.