关键词: 弹性波, 钻柱, 应力变化, 体积力作用

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.