Dynamic Modeling and Suppression Parameter Optimization for High-Frequency Vibrations in Deepwater Push-the-Bit Rotary Steerable Systems

Abstract With the advancement of hydrocarbon reservoir development into deepwater environments, the application of Push-the-Bit Rotary Steerable Systems (PTB-RSS) in deepwater drilling operations has become increasingly prevalent. However, due to the dynamic transmission characteristics of seawater riser systems, surface monitoring systems struggle to effectively capture downhole high-frequency vibration signals, posing significant challenges to the dynamic performance and operational reliability of Bottom Hole Assemblies (BHA) equipped with PTB-RSS. This study establishes a coupled dynamic model to elucidate the mechanisms by which engineering parameter variations induce High-Frequency Torsional Beating (HFTB) in BHAs. Innovatively, the upper drill string system is abstracted as a lumped mass-torsional spring-damper system to characterize its torque transmission behavior. For BHA dynamic analysis, critical factors such as mandrel friction effects under PTB-RSS steering forces and bit-rock contact torque are incorporated, leading to the development of a refined BHA dynamic model based on the Finite Element Method (FEM). By coupling these two modeling approaches, a comprehensive dynamic analysis model for PTB-RSS drill strings in deepwater systems is established, enabling efficient and accurate simulation of localized HFTB phenomena in BHAs. The simulation results demonstrate strong agreement with full-scale downhole vibration test data. Sensitivity analysis reveals that when the well depth reaches a critical threshold of 5,500 meters and the drill string rotational speed exceeds 240 rpm, the BHA enters an HFTB instability regime, where steering force adjustments fail to mitigate vibration responses. Applying this model to diagnose vibration conditions in a high-displacement well in Brazil’s Santos Basin confirms that the abnormal reduction in Rate of Penetration (ROP) at the 5,500-meter interval is fundamentally attributed to HFTB. This research pioneers the numerical reproduction of localized BHA HFTB through the construction of a multi-scale dynamic model for deepwater drilling. The revealed vibration induction mechanisms and critical engineering parameter thresholds provide theoretical foundations for vibration prediction and dynamic control of PTB-RSS BHAs in deepwater directional wells, offering significant engineering guidance for ensuring safe and efficient drilling in deepwater complex-structure wells.