Stick/Slip and Whirl Vibrations in Deepwell Drillstrings: Multidimensional Parameter Response Characteristics and Real-Time Quantitative Diagnosis

Summary

Deepwell drilling is strongly affected by drillstring vibrations, especially stick/slip and whirl, which threaten safety and efficiency. Despite the extensive development of downhole measurement tools, systematic quantitative characterization and mechanistic analysis of vibration features remain insufficient due to the unpredictability of complex downhole conditions. For this study, we utilized high-frequency near-bit measurements of engineering parameters and triaxial acceleration data, combined with surface logging data, to systematically analyze the dynamic characteristics of three typical operating conditions—normal drilling, pure stick/slip vibration, and coupled whirl/stick/slip vibration. Time-domain statistical analysis, fast Fourier transform (FFT), and short-time Fourier transform (STFT) methods are used to establish quantitative dynamic feature signatures for each condition. Results reveal that normal drilling exhibits a quasistatic equilibrium with a dominant lateral vibration frequency at the rotation frequency and an acceleration amplitude of 0.0145 g. In contrast, pure stick/slip conditions show extreme downhole rotational speed (revolutions per minute or RPM) oscillations [coefficient of variation (CV) up to 350%], with the lateral vibration frequency shifting to the stick/slip characteristic frequency and amplitude reaching 0.259 g. Coupled whirl/stick/slip conditions demonstrate anomalous downhole torque CV peaks (up to 100%) and a lateral vibration amplitude surging to 0.511 g, reflecting strong nonlinear torsional/lateral coupling instability. Based on these findings, three quantitative evaluation indices are proposed as follows: the stick/slip index (SSI) for torsional vibration severity, the whirl index (WI) based on the triaxial vibration energy ratio, and the whirl impact evaluation parameter (WIEP), which utilizes the kurtosis features of engineering parameters for low-cost whirl detection. Validation using continuous drilling data from two representative wells with distinct well trajectories, bottomhole assembly (BHA) configurations, and measurement-sub positions shows that the proposed indices respond rapidly to condition transitions. In particular, the WIEP preserves stable whirl-event contrast in both tested wells, providing initial field evidence for the engineering applicability of the index system. This research provides a theoretical and feature-engineering basis for real-time monitoring and intelligent recognition systems in deepwell drilling.