Madjid Kidouche

Drilling operations can encounter considerable challenges posed by strong, coupled vibrations that exert a complex influence on rotary drilling system performance. These vibrations are classified into three distinct types based on their propagation direction: axial, lateral, and torsional. Previous research efforts have predominantly focused on examining each vibration type in isolation. However, the effectiveness and resilience of developed controllers are profoundly affected by the often overlooked coupling effects arising from other types of vibrations. In this study, we propose the implementation of a Proportional-Integral-Derivative (PID) controller for the coupled Axial-Torsional vibration system. The research presented herein is dedicated to investigate the performance of the controller under strongly coupled vibrations. To address the dynamic vibrations encountered during drilling, it is imperative to understand the intricate behavior of the drill bit in response to these vibrations before designing controllers to mitigate their impact. Numerous models have been proposed in the existing literature to elucidate the behavior of the drill string under axial-torsional vibrations. The objective of this research is to develop a comprehensive model of the drilling system and investigate the robustness of the PID controller to mitigate the adverse effects of coupled Axial-Torsional vibrations. By effectively analysing the obtained results, this study has contributed to the optimization and improvement of drilling operations under sever coupled vibrations.

Hydrocarbon exploration and production activities are guaranteed through various operations including the drilling process, which is realized by using rotary drilling systems. The process involves crushing the rock by rotating the drill bit along a drill string to create a borehole. However, during this operation, violent vibrations can occur at the level of the drill string due to its random interaction with the rocks. According to their axes of occurrence, there are three types of vibrations: axial, lateral, and torsional, where the relentless status of the torsional vibrations is terminologically known as the stick-slip phenomenon. Such a phenomenon can lead to increased fatigue of the drill string and cause its abortive fracture, in addition to reducing the efficiency of the drilling process and consequently making the exploration and production operations relatively expensive. Thus, the main objective of this paper is to eliminate the severe stick-slip vibrations that appear along the drill string of the rotary drilling system according to the LQG observer-based controller approach. The rock–bit interaction term is highly nonlinear, and the bit rotational velocity is unmeasurable; an observer was first designed to estimate the unknown inputs of the model, and then the controller was implemented in the drill string model with 10 degrees of freedom. The estimation process was essentially based on surface measurements, namely, the current and rotational velocity of the top drive. Thereafter, the performance of the proposed observer-based LQG controller was tested for different simulation scenarios in a SimScape/Matlab environment, for which the controller demonstrated good robustness in suppressing the severe stick-slip vibrations. Furthermore, the simulation and experimental results were compared to other controllers designed for the same model; the proposed observer-based LQG controller showed better performance, and it was less sensitive to structured disturbances than H∞. Thence, it is highly recommended to use the proposed approach in smart rotary drilling systems.

The drilling process is among the most crucial steps in exploration and production activities in the petroleum industry. It consists of using mechanical mechanisms to crush rocks by the drill bit to pass through the different geological layers. The drill-string continuously transforms the rotational movement from the top drive motor to the drill bit through the drill pipes. Due to the strong interactions with the rocks, aggressive vibrations can arise in the drill-string in its three dimensions, and consequently, this may create three types of synchronous vibrations: axial, lateral, and torsional. The severe status of the latter is known as the stick-slip phenomenon, and is the most common in rotary drilling systems. Based on field observations, it has been inferred that the high frequency stick-slip vibrations may lead to drill-string fatigues and even to premature rupture. In the best case, it reduces the drilling efficiency by decreasing the rate of penetration, due to which the drilling operations become proportionally expensive. The main novelties of this research work are the design of an H∞ observer-based controller to mitigate the high frequency stick-slip vibrations, and the quantitative analysis of the vibrations’ severity for ten degrees of freedom model. The observer is designed to estimate the non-measurable rotational velocity of the drill bit due to the severity of the vibrations, while the controller is dedicated to suppressing the vibrations by using the top drive inputs. Thus, many scenarios have been considered to test and analyze the observer performance and the controller robustness. Furthermore, a comparison with the LQG observer-based controller has been conducted, where H∞ has demonstrated better efficiency in suppressing the stick-slip vibrations under unstructured perturbations.

The main objective of this paper is to suppress the stick–slip vibrations in the drilling system so that the drill bit can follow the desired nominal angular velocity of the Top Drive in an optimal time. Hence to protect drilling equipment from hazards and increase drilling performances by decreasing the non-productive time (NPT). Three control systems have been proposed to achieve this objective, a sliding controller is firstly designed and then a backstepping approach is discussed secondly. Furthermore, a hybridization of sliding mode control with a backstepping approach has been proposed on the so-called hybrid backstepping sliding mode controller. The latter has not been proposed before in the literature for rotary drilling systems. Moreover, two torsion models of the system have been discussed for different degrees of freedom. Based on the comparison between controllers’ responses, the effectiveness and the robustness of the hybrid controller have been demonstrated and highlighted, whose fast response can protect the drilling equipment from hazards that may be caused by the slip phase of the vibrations. Hence, it is recommended to implement the proposed controller in smart rotary drilling systems for petroleum industry.