Abstract
Drilling is one of the most costly and risky activities in oil and gas reservoir exploration and field development. A portion of this high cost is related to unwanted vibrations of the drill string. Assumed as the primary cause of many problems, drill string vibration is an ongoing challenge for drillers. In this paper, the lateral vibration characteristics of drill string in the highly deviated well are quantitatively analyzed and the influence of different drilling parameters on lateral vibration are fully evaluated.
In order to study the lateral vibration characteristics of drill string in the highly deviated wells under different drilling parameters, a drill string dynamics simulation apparatus was built according to the similarity theory, and the vibration response in different directions was measured. The lateral vibration frequency of drill string was calculated by Fast Fourier Transform (FFT) and the non-dimensional frequency was defined to quantitatively evaluate the relationship between the vibration frequency and the excitation frequency. Moreover, the average acceleration was defined to evaluate the movement of the drill string in a period of time.
The results indicate that rotary speed is the determining factor of drill string's lateral vibration. The lateral vibration frequency is equal to the excitation frequency and the average acceleration generally increases at a relatively low rotary speed. As the rotary speed continues to increase, when it exceeds a certain critical point, the lateral vibration frequency doubles and the average acceleration encounters a shape increase. In addition, with the increase of the weight on bit (WOB), the vibration frequency and the average acceleration keep stable, but the phenomenon of doubling the vibration frequency is suppressed.
