Ultra High Torsion Drill Pipe Joint Thread Research

With the fast development and wide application of advanced drilling technique of ultra deep well, directional well, large displacement well and so on, the torque load in drilling work has increased significantly. The increase of torque load has then led to failures of drill string. The investigation on domestic oil and gas fields shows that hundreds of accidents caused by drill string failures exist because the lackage of anti torsion in the drill string connections and the failure of traditional drill pipe connection thread structures in meeting the high anti torsion requirements on performance of the above wells. Therefore, studying on the drill pipe thread of strong anti torsion is of great importance. In this paper, the research based on the above situation mainly including the following aspects:(1) The thread structures are of complex shape and multiple small surfaces. The existing modeling method can not accurately represent the current deformation coordination relation between joint threads. Thread Angle joint finite element calculation model is established, and the accuracy of the built model calculation results is verified by referring to the experimental data. This model shall be used to analyze mechanical properties under tensile bending and compressive wernching conditions and under various loading situations.(2) A new type of ultra high torsional tool joint thread structure is proposed to deal with failures of drill pipe joint thread caused by excessive torque. The following key structural parameters of the new ultra high torsional drill pipe joints are optimized by Orthogonal Optimization:taper gage, thread pitch, tooth height, thread angle, master shoulder Angle and secondary shoulder Angle. The optimal combination scheme for the key structural parameters of the new ultra high anti torsion drill pipe joints is:taper gage 1:20, thread pitch 3.5 teeth/inch, tooth height 3.595mm, thread angle 20 °, the master shoulder Angle 60 ° and secondary shoulder Angle 80 °. Sequence for impact of each parameter on anti torsion as as follows:thread angle, tooth height, taper gage, thread pitch, master shoulder Angle and secondary shoulder Angle. And further analyze the impact of the gap volume size on the secondary shoulder place of the new ultra high torsional tool joint thread on its mechanical properties, and range is recommended to be within 0.05～0.1 mm through comparation and analysis.(3) Calculate the stress field distribution of the new ultra high torsional drill pipe under torque load, tensile load, bending load and compression load, and constrastively analyze the anti-torsion property, anti-tension property, anti-bending property and anti-pressure property of the new ultra high torsional drill pipe and API structure and double shoulder structure. The results show that the anti-torsion property of the new ultra high torsional tool joint thread structure is about 50% higher than that of the API structure, and 25% higher than the double shoulder structure.(4) By calculating the load capacity of the ultra high torsional tool joint, yeild limits of the new ultra high torsional resistance load of drill pipe joint thread under various composite load conditions are obtained. The obtained results shall provide reference for on-site selection and choice for adoption of the new ultra high torsional tool joint thread.