Robust output-feedback control of 3D directional drilling systems

Abstract

The amount of mineral and energy resources in conventional reservoirs has been drastically diminished in recent years. This has led to the development of techniques to reach reservoirs which are not easy to access and, more specifically, where boreholes with complex geometries need to be drilled. Directional drilling allows to accomplish such complex boreholes. Although this process is not new to the industry, its complex dynamics have been responsible for the development of both numerical models and closed-form models in terms of delay differential equations. Such models can be used to predict the evolution of a borehole or to develop control strategies. Current state-of-practice control methods are basically open-loop techniques, where an operator has the task to steer the drilling system while trying to follow a reference for the borehole trajectory. This usually generates undesired behavior such as borehole spiraling and kinking. In order to provide a way to avoid these undesired effects, novel control strategies need to be designed to improve the directional drilling process. In order to improve the performance of this type of processes, some efforts have been made to propose a control strategy. One of the most recent approaches makes use of the model developed by Perneder and Detournay (PD) at the University of Minnesota, which describes the three-dimensional evolution of the borehole, with a set of nonlinear delay differential equations. The proposed control strategy implements a state-feedback controller to this model; hence it relies on availability of full-states measurements, which are not available in practice. The goal of this thesis project is to extend this controller design making use of only local measurements of the orientation of the bottom-hole assembly. This is accomplished by including an observer in the control structure. Furthermore, the proposed controller design is robust against parameter uncertainty. The approach taken considers initially the case where the bit does not exhibit the so-called bit walk, simplifying the controller design. The effectiveness of the resulting robust output-feedback control approach is illustrated on realistic drilling scenarios.