Abstract
Friction reduction devices in the form of vibrators are becoming more widely used in drilling operations because of their ability to create oscillation in the string, which can reduce the amount of friction force present. Ordinarily, the placement of vibrators is based on past field experience; an improper arrangement of vibrators, however, can reduce their efficiency and lead to possible tool damage. A proper model for estimating the working range for vibrators can enhance the efficiency and safety of the vibrator.
This paper presents a new method for predicting the working range for vibrators based on the stress wave theory. The proposed method uses the stress wave theory to calculate the vibration velocity. Beginning at the vibrator, the stress wave travels a lengthy distance in the string. The friction on the string, however, diminishes the stress wave energy until the vibration velocity reaches zero. The vibrator working range is defined as the string section with a non-zero oscillation velocity.
A set of equations to calculate the stress wave traveling distance is proposed in this paper. This model provides a theoretical prediction of the vibrator working range to effectively optimize vibrator use. The stress wave traveling distance predicted from this model is likely to be a linear relationship to the acceleration generated by the vibrator, which is similar to the results obtained in the field, and can be used to better determine the most effective placement for vibrators in horizontal wells.