Abstract: When a drill string moves upward or downward in a well,significant stress variations at the suspension point are caused by the starting and stopping of the motion.The maximum stress variation takes place at a moment that the motion stops when the drill string goes upward.A velocity wave and a stress wave resulting from the stress variation are transmitted downward along the drill string.On the basis of the solution of one-dimensional wave equation with body force acting this paper gives the calculation of su- dden velocity change at any cross-section and sadden variation of the mud pressure Thereby the phenomena that happened do wnhole can be explained.The damage of downhole tools caused by a sudden velocity change and a cou-nter-pressure-difference are also explained.It is suggested that regardless of the direction of string motion either upward or downward,smooth and gradual stopping is extremely important.

摘要： 钻柱在上提、下放的开始和终了悬点的应力要发生很大变化,其中以上提过程的终了时变化最大.悬点的应力变化产生速度波和应力波沿钻杆向下传递.本文在解有体积力作用下的一维波动方程的基础上计算钻柱截面的突发速度及泥浆压力的突发变化.从而说明井下发生的现象,说明钻柱的突发速度和井下发生的反压差对井下工具的破坏作用.由本文的分析可以看出钻柱不论是上提还是下放,缓慢停止是非常重要的.

关键词: 弹性波, 钻柱, 应力变化, 体积力作用