A zone predictive safety filter for drill string torsional vibrations control considering measurement delay and data loss

Abstract

During drilling operations, bit fatigue and failure caused by undesirable vibrations frequently lead to substantial increases in drilling time and costs. Among these vibrations, the torsional vibration, whose severe form is also known as stick–slip oscillation, represents one of the most destructive vibrations. Existing advanced control methods, such as Sliding Mode Control (SMC) and Robust Control, often face limitations, including difficulties in on-site deployment and measurement delays or data loss in downhole data. This study proposes a novel “plug-and-play” approach that augments the existing torsional control system through the integration of two key modules: the Zone Predictive Safety Filter (Zone PSF) and Robust Moving Horizon Estimator (Robust MHE). The Zone PSF module detects and eliminates the stick–slip oscillations in real time. This ensures the safety of the drilling system throughout the drilling process. The Robust MHE module addresses bit rotational speed estimation challenges under time-varying measurement delays and data loss scenarios. It employs adaptive gain technology to maintain the stability of the estimation process even in non-Persistently Exciting (PE) drilling conditions. Finally, the numerical simulation results indicate that the proposed method yields superior control performance and robustness for the torsional control system.