Experimental study of dynamic characteristics of drillstring in highly deviated well

Key words:  drilling  highly deviated well  drillstring dynamic characteristic  lateral vibration  acceleration  trajectory offset

Abstract:

In order to investigate the dynamic characteristics of drillstring in highly deviated wells, a drillstring dynamics simulation equipment was built based on the similarity theory. The actual trajectory of the drillstring movement in the simulated wellbore was plotted based on the experimental results, and the dynamic characteristics of the drillstring were quantitatively evaluated in terms of lateral vibration, acceleration and trajectory offset. The results indicate that the rotary speed of the drillstring is the dominating factor for its dynamic characteristics. When the rotary speed is low, the lateral vibration frequency is equal to the rotation frequency of the drillstring and the average acceleration increases linearly. When the rotary speed is high, the lateral vibration frequency doubles and a rapid increase of the average acceleration can occur. In addition, weight on bit has no significant influence on the dynamic characteristics of the drillstring. Moreover, with the increase of the inclination angle of the wellbore, the vibration amplitude and frequency of the drillstring can remain stable, whereas its trajectory offset increases. In order to avoid severe vibration, the rotary speed should be less than 69.4 r/min during drilling operations.