Research On Three-dimensional Mechanical Properties And Structural Improvement Of Drill Pipe Joints In Complex Structure Wells

With the wide application of ultra deep well,horizontal well,directional well,large displacement well and highly deviated well drilling technologies in petroleum drilling engineering,the premature failure problem of drill pipe joint caused by underground complex working conditions is increasingly prominent,resulting in the increase of drilling period and drilling cost.Such problem has become one of the main factors to restrict drilling efficiency.Currently,many drill pipe joints serving in China,are foreign product or foreign technology structure.It needs a lot of fee and royalty payment,causing the processing enterprises of drill pipe joint to high investment,high risk and low profit.In recent years,many domestic and foreign scholar have conducted a lot of research on drill pipe joint,but are mainly focused.on the 2D axisymmetric model,a few use of 3D mechanical model and it does not consider the influence of the angle of thread and the bending of the hole at the same time.Rare research has been reported on mechanical property of drill pipe joint in complex structural well and the super high anti twist double shoulder drill pipe joint.In view of the above problems,a 3D numerical simulation model of drill pipe joint and the converted model of borehole curvature to loading moment have been established based on the principle of virtual work,Von Mises yield criterion and nonlinear contact theory.It considers the influences of the angle of the thread and the bending of the hole.So as to study the make-up property and the influences of internal and external pressure difference,wellbore temperature,friction torque,uniform wear and borehole curvature on safety of drill pipe joint.To calculate the ultimate bearing capacity of drill pipe joint by considering preload,bending load and dynamic load safety factor.The max stress concentration factor of drill pipe joint is calculated,and the effect of friction coefficient on the stress concentration factor is analyzed.Based on the material S-N curve,the theoretical model of the bending fatigue S-N curve of drill pipe joint is determined,and the accurate fatigue finite element calculation model is established.To calculate fatigue life of drill pipe joint under composite alternating load by using the multi axis fatigue algorithm,and analyze the influences of residual stress and surface quality on fatigue life.Based on the deformation coordination relationship of drill pipe joint,a kind of excellent performance of the super high anti twist double shoulder drill pipe joint is designed by using the orthogonal optimization method.Compared with the bearing performance and fatigue performance of the super high anti twist double shoulder drill pipe joint,ordinary double shoulder drill pipe joint and API drill pipe joint.So as to analyze the make-up property of the super high anti twist double shoulder drill pipe joint and its 3D mechanical property in the curved section.Research results have shown that the make-up torque can provide a certain initial contact pressure for drill pipe joint to ensure its connection strength and sealing performance in drilling operation.The make-up torque improper control can reduce the safety of drill pipe joint.The friction torque,uniform wear and borehole curvature have great influences on the connection performance of drill pipe joint.In consideration of random vibration and shock of service,the drill pipe joint used for complex well should be designed and selected based on the influences of friction torque,wear and borehole curvature.For each kind of drill pipe joint to be designed,the accurate numerical calculation of the ultimate working pull and the ultimate working torque should be conducted on the corresponding borehole curvature and axial tensile load to ensure work safety.The introduction of residual compressive stress and improving the surface quality can significantly improve the fatigue life of drill pipe joint.The optimal combination of parameters of the super high anti twist double shoulder drill pipe joint is taper 1:16,pitch 6.55mm,guiding plane angle 29°,bearing surface angle 28°,tooth height 3.755mm.Compared with API drill pipe joint and ordinary double shoulder drill pipe joint,the super high anti twist double shoulder drill pipe joint tensile strength increase 10.65%and 9.26%,torsion strength increase 62.50%and 21.35%,bending strength increase 2.75%and 1.38%,compression strength increase 52.00%and 5.56%.The super high anti twist double shoulder drill pipe joint tension compression fatigue life increase 1.19 times and 0.92 times,bending fatigue life increase 1.74 times and 1.22 times,torsion fatigue life increase 550 times and 57 times,composite fatigue life increase 28.79%and 15.45%.