Advanced 4D Drilling Dynamics Model Simulates Downhole Vibration and Helps to Optimize in Preventing Drill String Failure

Abstract Downhole vibration, such as backward or chaotic whirling, is one of the primary causes for drill string failure during drilling operation. Understanding drilling dynamics is crucial for determining the mechanism of vibration and fatigue accumulation so as to mitigate risk of drill string failure. Drilling dynamics or vibration data can either be obtained from real-time measurement or simulation based on dynamics model, which plays a crucial role for drilling optimization in pre-drill planning phase. An advanced 4D drilling dynamics model, which considers the interaction between drill bit and formation, impact and friction between drill string and wellbore, constraints exerted on drill string and drill bit, is proposed to simulate the distribution and variation of 3D displacement, velocity, acceleration as well as the stress state of entire drill string within specified time period. This time domain model allows exploration of the full range of dynamics response under different drilling scenarios, which helps to optimize the performance and reliability of BHA as well as WOB/RPM selection. Moreover, drill string fatigue life prediction can also be achieved by combing simulated stress state and fatigue accumulation theory. Simulation shows that BHA with smaller- sized drill collar or fewer stabilizers are more susceptible to backward and even chaotic whirling while drilling. Also, inappropriate WOB/RPM combinations such as low WOB with high RPM could also cause the onset of severe lateral vibration. High frequency bending stress, mainly concentrated on BHA and caused by lateral vibration, is the main reason for rapid fatigue accumulation and continuous severe vibration could even result in drill string fatigue failure within hours. These findings helped to justify the 5 consecutive BHA failure and 1 washout while drilling the 171/2" wellbore with 7621 ft length of an ultra-deep well. Simulation also showed that downhole lateral vibration severity was significantly reduced after optimizing drill bit design, adopting BHA with larger stiffness and optimizing drilling parameters, which guaranteed the successful drilling of a new 171/2" wellbore with 4659 ft length of another offset well without downhole accident. This 4D drilling dynamics model could be used to conduct comparative analysis of dynamics responses based on specific criteria to identify the optimum BHA design and drilling parameters, which shows great potential in drill string fatigue failure prevention and drilling optimization.