Analysis And Optimization Of Mechanical Characteristics Of Drill Pipe Thread Joint

In oil drilling,downhole drilling tools such as drill pipe,drill collar and adapter are connected by threads.During the working process,the drill pipe thread carries multiple composite loads such as tension,compression,bending and torsion.At the same time,due to the impact of drilling fluid erosion,drill string vibration and other conditions,the drill pipe thread has been damaged and failed,such as gluing,tripping,puncture and leakage.With the increasing number of deep wells and ultra-deep wells,the failure rate of drill pipe threads is increasing under high load conditions.Therefore,it is urgent to improve the strength of drill pipe thread connection to meet the drilling requirements of difficult development wells such as deep wells and ultra-deep wells.For this reason,this paper mainly aims at the shortcomings of the existing conventional drill pipe threads,such as serious stress concentration and uneven load distribution,designs a new type of special drill pipe thread structure,establishes a finite element model for simulation analysis,and completes the overall study of the conventional drill pipe thread joint and the special drill pipe thread joint.The paper mainly carried out the following work:(1)Analyze the mechanical properties and failure forms of drill pipe thread connection,and understand the types and structural characteristics of standard drill pipe threads and special drill pipe threads on the market at present;Analyze the mechanical properties of drill pipe thread,study the basic load acting on the drill string,and theoretically analyze several loads acting on the drill pipe threaded joint;Investigate the forms of drill pipe thread failure,including fatigue failure,slip failure,thread failure,seal failure,overload fracture and buckling deformation,and discuss the measures to reduce drill pipe thread failure.(2)The double shoulder threaded joint is designed,and the API threaded joint and double shoulder threaded joint are 3D modeled.The ABAQUS simulation software is imported for mesh generation,material setting and boundary condition setting.(3)Through comparative analysis of stress distribution and size of API threaded joint and double shoulder threaded joint under different axial tension,axial compression and bending loads and torsion loads,it can be found that the stress of double shoulder threaded joint is superior to that of conventional API threaded joint.(4)Apply the combined loads of axial tension and bending load,axial tension and torsion load,bending load and torsion load to the two types of threaded joints,compare and analyze the stress distribution and size of the threads of the two types of threaded joints,and obtain the ultimate working torque under different tensile loads.It is found that the thread teeth of double shoulder threaded joints have better tensile and torsional capacity than conventional API threaded joints.Then,the layout is made to provide reference for rational use.