中文摘要：

自动垂直钻井系统在工作中，导向活套与钻杆要有一个相对转速。导向活套在与钻杆连接轴承的摩擦转矩的作用下而随钻杆转动，而井下返程泥浆在通过活套时也会产生阻碍活套转动的反向扭矩，该反向扭矩是保证活套与钻杆存在相对转速的一个关键因素。利用FLUENT软件包对活套井下泥浆流场进行建模仿真，揭示了泥浆通过活套时的流动特性。计算结果表明泥浆对活套的反向扭矩取决于泥浆的流量、活套转速等多种因素，且只要钻杆转速超过平衡钻杆与活套的摩擦转矩的临界转速，该反向扭矩就可以使活套与钻杆间产生相应的转速差。

英文摘要：

When the automatic anti-deviation drilling system is in operation, a relative rotate speed is needed between the steerable sleeve and the drill string. The steerable sleeve rotates as a result of the friction torque exerted by the bearing connecting the sleeve and the drill string, while the backtracking muds pass through the sleeve and produce a reverse torque preventing the sleeve from rotating, which is a key factor to ensure a relative rotate speed between the sleeve and the drill string. The CFD software Fluent was used to model the flow field of the down-hole muds, and explore the flow characteristics. The simulation results indicated that the value of the reverse torque depends on several factors such as the mud flux, the sleeve rotate speed and so on, and as long as the rotate speed of the drill string exceeds the critical rotate speed, the reverse torque by the muds to the sleeve is sufficient to produce a relative rotate speed between the sleeve and the drill string.