Dynamical Stability Analysis and Optimization of Antistall Tools for Stick-Slip Vibration Mitigation in Rotary Drilling Systems

Abstract Stick-slip vibration, a severe torsional instability in rotary drilling systems, significantly impairs drilling efficiency and can lead to catastrophic failures. Antistall tools (ASTs) offer a passive mechanical solution to mitigate this detrimental phenomenon. This study presents a comprehensive investigation into the dynamical stability analysis and parameter optimization of drilling systems equipped with ASTs. A reduced-order dynamic model using the lumped-mass method is developed, incorporating nonlinear Stribeck friction at the bit and the mechanical properties of the antistall tool (AST). The model was then linearized and nondimensionalized to derive a normalized parametric representation. Based on this normalized model, rigorous stability analysis criteria were established, and stability boundaries were mapped in the relevant parametric space to identify stable operating regions. This stability analysis framework facilitated the optimization of key AST parameters, including damping, installation location, and constraint constant. The optimization aimed to expand the system's stability region, particularly enabling stable operation under larger negative damping conditions often associated with higher weight-on-bit (WOB). The analysis revealed that installing the AST close to the drill bit is optimal for enhancing stability. Time-domain nonlinear simulations were conducted to validate the findings, comparing systems without AST, with nonoptimized AST, and with optimized AST under varying WOB and rotational speeds. Results demonstrated that the optimized AST configuration effectively suppresses stick-slip vibrations even under conditions prone to instability, significantly reducing vibration amplitude and stick duration by dynamically adjusting axial deformation to counteract sticking and slipping phases. This research provides a systematic methodology for optimizing AST design to improve drilling performance.