Abstract：Using the mathematical model of longitudinal vibration of drill string, the authors analyzed the characteristics of the axial stress amplitude distribution curve and the maximum axial stress amplitude-frequency curve in the drill string and the impact of drilling fluid viscosity, bit displacement, shock absorber’s installation position on the maximum axial stress amplitude in the drill pipe. Analysis shows that: the axial stress amplitude along the drill string appears in waveforms and the point of the maximum axial stress amplitude is at the bottom of drill string or in drill pipe; the rotary speed-dependent curve of the maximum axial stress amplitude in drill pipe appears at least one pit, and the speed between the margins of the pits should be chose when drilling a well; the variation trend of the maximum axial stress amplitude in drill pipe with rotary speed does not quite fit in with that of the axial stress amplitude at the bottom of drill string with rotary speed, and the former but not the latter should be the target for resonance judging and rotary speed optimizing; the maximum axial stress amplitude in drill pipe varies roughly directly with the bit displacement; the higher viscosity of drilling fluid is, the smaller the maximum axial stress amplitude in drill pipe is; a shock absorber can change the natural frequency of a drill string, and the shock absorber should be fixed close to the bit when drilling with low rotary speed and kept a certain distance with the bit when drilling with high rotary speed to protect the drilling tools more effectively; optimizing make-up of a drill string and rotary speed can prevent drilling tool failure effectively
2011, Vol. 30 
