Measurement of the Downhole Drill String Vibration Signal and Analysis of the Vibration Excitation Sources

To deeply understand the downhole drill string vibrations and clearly identify the vibration excitation sources in the drilling process, the vibration signals were measured during rotary drilling of an ultra-deep well by the ESM (environmental severity measurement) storage system. According to the principle of measurement, the stick-slip and whirling vibrations of the drill string were studied. On this basis, the frequency domain and time frequency of drill string vibrations were analyzed by the fast Fourier transform and short-time Fourier transform. Then the main frequency causing drill string vibrations was determined, and the vibration excitation sources were further identified. The results demonstrated that during the stick-slip vibrations of the drill string, the triaxial acceleration changed synchronously and periodically, with a period of 10 s and a main frequency component of 0.1 Hz. When the drill string experiences whirling vibrations, the three-axis acceleration fluctuated disorderly and irregularly, and the main vibration frequency was twice the bit speed frequency, 1 to 5 times the rotary table speed frequency. The case analysis result showed that excitation sources causing the whirling mainly consisted of the interaction between the drilling bit and the formation, the friction between the stabilizer or Power-V system and the borehole wall, etc.