With the continuous increase in the drilling depth of oil and gas wells, drill pipes are subjected to greater axial forces and torques. As a relatively weak structural component, drill pipe threads require mechanical strength analysis and structural optimization. Finite element analysis (FEA) models was established for the mechanical behavior and crack propagation of standard API(American Petroleum Institute) threaded joints and structurally optimized non-standard new threaded joints under multiple working conditions. The FEA results show that the non-standard new joint has higher mechanical strength, it is easier and faster to make up, and features three non-working threads, which reduce the stiffness at the large end of the threaded joint and alleviate stress concentration problems. Specifically, the torsional strength of the non-standard joint is 23.86% higher than that of the standard joint, the cross-sectional stiffness at the thread root is increased, and the crack propagation lengths at the third internal and external shoulder threads are significantly reduced. This effectively suppresses crack propagation, with fracture wall thickness reduced by more than 40%. During the drilling process of the 10 000 meter ultra deep Chuanke 1 well developed in Sichuan, the non-standard new type of threaded joint will be used. The research methods and results in this article provide a theoretical basis for the design of non-standard new drill pipe threads in ultra deep wells.
SONG Dong-dong, LUO Xin, HE Ming-min, WAN Zhi-yong, CHEN Jian, WANG Hao, LIAN Zhang-hua.
Design and Evaluation of New Drill Pipe Thread Joint in Ultra-deep Well Based on XFEM[J].
Science Technology and Engineering, 2026, 26(7): 2857-2875 DOI:10.12404/j.issn.1671-1815.2501769
在钻井过程中钻杆接头需要承受较大的轴向力和扭矩,还需确保钻杆接头工作时公母螺纹紧密连接,防止因连接不牢导致钻杆断裂或脱落事故,且上扣扭矩的大小直接影响钻杆接头螺纹的啮合程度和贴合度,足够的上扣扭矩可以使螺纹牙、主台肩、副台肩等啮合面产生足够的接触压力,从而实现接头工作时的预紧和密封,若需获得准确的上扣扭矩值大小,必须计算钻杆接头的扭矩强度,其中API RP 7G标准推荐了扭矩强度理论计算数学模型,外台肩和内台肩扭矩强度计算公式分别为
为进一步分析螺纹齿根圆角处裂纹扩展路径,将裂纹扩展过程中对网格的损伤程度提取,内外台肩附近扣根圆角处裂纹扩展情况分别如图20和图21所示,可知损伤集中于初始裂纹处,因为在扩展有限元方法(extended finite element method, XFEM)分析方法中,给定的初始裂纹是代表完全损伤,但在裂纹扩展路径上的单元是发生的断裂,并没有出现高速冲击产生的损伤而脱落,于是未出现高等级损伤,与图17中观察到的螺纹接头裂纹扩展情况相同。从图20和图21可以看出,裂纹扩展方向均是从螺纹扣根圆角处向壁面,尤其是在螺纹接头外台肩危险位置处裂纹扩展情况严重,当该种螺纹使用在超深井钻井过程中,面对较大的轴向自重载荷和钻杆内外壁压差时,将出此较严重的抗裂纹扩展性能衰减,需要针对该种结构进行优化设计。
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