Abstract: The stress concentration is a key factor causing fatigue failures.It is very important to make a quantitative research on the stress level and distribution characteristics of BHA.The finite element mechanics models for BHA with stabilizers in vertical well or in slant hole were established.The models were solved by the software,and deformation field and the stress field were computed.For BHA,the results show the highest deflection is located in the long span between the stabilizers.The most dangerous position is in the location of deformed drillstem with the biggest corner.The biggest corner is located near the stabilizers,so there is the highest bend moment.The stress level in the position of stabilizer is the highest,and the stress of other places is much lower.Because the threaded connections are just located in these highest stress areas of the drill tool,the fatigue failure of the threaded connections may easily happen.The fatigue failure of the stabilizers almost occur in the positions of threaded connections.

Key words: BHA, stabilizer, deformation, stress, FEA, research

摘要： 应力集中是钻具疲劳破坏的一个关键因素,定量计算钻具在井下所承受的应力水平及其分布规律显得尤为重要。建立了带扶正器下部钻具组合在垂直井和斜直井眼中的有限元力学模型,用编制的软件求解并得到了下部钻具组合的形变和弯曲应力。揭示了下部钻具组合失效的力学机理。下部钻柱组合在长跨距内变形挠度最大。钻柱变形后,危险点不在挠度最大处,而在钻柱变形转角大的位置。在扶正器附近的转角大,因而弯矩也大。扶正器附近是应力集中区,而远离扶正器的两跨之间应力水平相对较低。从钻具的结构上看,钻具的连接螺纹正处在这些最大应力集中区,这是连接螺纹疲劳失效的根本原因,而扶正器或配合接头的失效多发生在连接螺纹部位。

关键词: 钻具组合, 扶正器, 有限元法, 变形, 应力, 计算模型