Effect of drill string lateral vibrations on wellbore stability and optimal mud pressure determination

Wellbore instability is a critical issue in drilling operations, contributing to significant non-productive time and costly delays. While previous studies have focused on physicochemical and mechanical causes of wellbore instability, the effects of drill string vibrations-particularly cyclic impacts on the wellbore wall-remain underexplored. This is because history dependence and the gradual degradation of rock strength due to fatigue is notoriously difficult to model accurately. The study investigates the impact of drill string lateral vibrations on wellbore stability, with a specific focus on how these vibrations influence the optimal mud pressure required for maintaining wellbore integrity. Using a customized poro-elasto-plastic damage model, a series of numerical simulations were conducted. In this study, the impact of pore pressure is included in the effective stresses and the results indicate that while increasing mud pressure reduces the plastic strain under static conditions, the presence of drill string-induced cyclic impacts significantly raises the likelihood of wellbore failure, particularly at higher mud pressures. A key finding emphasizes the need to account for both static and dynamic loading conditions when determining the optimal mud pressure, particularly in situations where drill string vibrations are likely to occur. This research highlights the importance of incorporating drill string dynamics into wellbore stability assessments to minimize failure risks, reduce non-productive time, and enhance drilling safety.