Modeling and analyzing the motion state of bottom hole assembly in highly deviated wells

Motion state of bottom hole assembly (BHA) has a great effect on the performance of downhole drilling tools. In this article, we developed a finite element model for characterizing the lateral motion of BHA in highly deviated wells taking discontinuous interaction between drill strings and wellbore into consideration. Numerical simulations were conducted by solving the motion equation through Newmark method. To verify the established model, an indoor experimental apparatus was built based on the similarity criterion. Numerical and experimental simulation results were compared and analyzed under different rotary speed, weight on bit (WOB) and well inclination condition. Both of the results showed that BHA locates in and swings along the lower right part of borehole in highly deviated wells without forming into backward whirl motion. Rotary speed has an obvious effect on BHA lateral motion state where the vibration amplitude and frequency get improved with the increase of rotary speed. Compared with rotary speed, WOB and well inclination angle has a much smaller effect on the BHA lateral motion in highly deviated wells. Based on the analyses, relevant recommendations were given for the engineering practical use. This study can help understand the dynamic characteristics of BHA in highly deviated wells and select operation parameters for better drilling.