Optimized Design Of New High-strength Drill Pipe

As the depth and difficulty of oil-gas well drilling constantly increase, the proportion of complicated well drillings such as deep well, ultra deep well, horizontal well is growing at home and abroad, and complicated well drilling operation becomes more and more demanding for drill pipe. For purpose of this paper, investigation and survey on new-type drill pipe products made by some famous manufacturers were carried out to learn about the development situation of drill pipe, and design of tool joint and of drill pipe body was optimized with finite element method and the theoretical strength formula recommended by API RP 7G on this basis with an aim to enhancing strength, mitigating stress concentration and improving hydraulic performance. This paper mainly:(1) Analyzed the feasibility of using V150 steel grade new-type high strength pipe material for drilling tool; carried out routine mechanics performance test and stress corrosion crack resistance test for V150 steel grade pipe material and API S135 steel grade pipe material respectively (results showed that V150 steel grade new-type high strength pipe material is superior to S135 steel grade pipe material in respect of both mechanical property and stress corrosion crack resistance), providing a basis for material selection and strength design of new-type drill pipe.(2) Selected two types of representative tool joint to make finite element analysis and comparison under combined loadings, to figure out the characteristics of stress distribution of both types, and compare the performance of both types from the aspects of the uniformity of bearing of thread engagement section of tool joint and the stress concentration factor of screw tooth root.(3) Designed a new-type high strength large borehole double-shoulder tool joint based on the analysis of the influence of drill pipe joint structure parameters on torsion strength and of structure characteristics of drill pipe joint, with an aim to enhancing torsion strength of tool joint, mitigating stress concentration and improving hydraulic performance; according to theoretical calculation, the torsion strength of the new-type double-shoulder tool joint is higher than that of GPDS 50 tool joint by 27.7%, and than that of API NC50 tool joint by 76.4%; besides a higher torsion strength, the borehole diameter and wear allowance of the new-type double-shoulder tool joint are also superior; according to finite element analysis, the stress peak value and the stress concentration factor of thread tooth root of the new-type double-shoulder tool joint are lower.(4) Designed a new-type high strength low pressure loss drill pipe body based on the analysis of the influence of drill pipe body size on strength and hydraulic pressure loss, with an aim to enhancing the combined tensile and torsional strength and reducing hydraulic pressure loss; optimized the R value and Miu value of the upset transition area based on three-dimensional finite element analysis of the upset transition area under tensile, torsional and bending load, mitigating stress concentration in the upset transition area of the new-type drill pipe body.The foregoing information provides a whole set of optimization design method of drill pipe, including material selection, structure design, structure optimization, etc.. On this basis, drill pipes of different performance and with different functions can be designed, providing a reference for optimization design of new-type drill pipe.