Managing Drilling Vibrations Through BHA Design Optimization

Summary Significant performance improvement has been achieved by successfully managing drilling vibrations through bottomhole-assembly (BHA) redesign. This effort has resulted in increased footage per day and reduced tool damage. Prior literature has described improvements in operating practices to manage vibrations (Dupriest et al. 2005; Remmert et al. 2007) as a key component of this rate-of-penetration management process. In a parallel work activity, BHA redesign efforts have provided additional performance improvements of approximately 36% in one drilling application. Dynamic modeling of the BHA has identified the key design changes leading to these improvements. The redesigned BHA has lower calculated vibration indices than the standard BHA. The BHA design evaluation process uses a frequency-domain lateral dynamic model in both predrill forecast and post-drill hindcast modes. BHA lateral vibrations are characterized such that alternative BHA configurations may be developed and compared directly with a proposed baseline assembly. In the hindcast mode, the BHA model can be operated at the recorded weight on bit (WOB) and revolutions per minute (RPM) to generate corresponding model results in time or depth, and these values can be compared with the measured performance data. In one case study, the redesign of a BHA with downhole motor and roller reamer is described, with corresponding field data for four original BHAs and four redesigned assemblies. In a second application, model and field drilling results for two rotary-steerable assemblies are compared to evaluate the predictive ability of the model in smaller hole size and with different BHA types. Finally, the utility of the model to identify preferred rotary-speed "sweet spots" is demonstrated in a motor BHA operating in larger hole.