A challenge for precise positioning in nanopositioning using smart materials is hysteresis, limiting positioning accuracy. The Preisach model, based on the delayed relay operator for hysteresis modelling, is introduced. The model is identified from experimental data with an input function ensuring information for all input levels. This paper presents implementational issues with respect to hysteresis compensation using the Preisach model, showing the procedure to follow, avoiding pitfalls in both identification and inversion. Issues due to the discrete nature of the Preisach model are discussed, and a specific linear interpolation method is tested experimentally, showing effective avoidance of excitation of vibrational dynamics in the smart material. Experimental results of hysteresis compensation are presented, showing an approximate error of 5% between the reference and measured displacement. Consequences of an insufficient discretization level and a high frequency reference signal are illustrated, showing significant deterioration of the hysteresis compensation performance.

Increased use of Managed Pressure Drilling (MPD) has enabled a significant improvement in drilling operations through the ability to accurately control pressure within a narrow window and by actively managing the annular pressure profile. However, the technology has not yet reached its full potential; well control events involving a gas influx causes two-phase flow in the well and can lead to severe deterioration of pressure control performance. In this study, a robust model-based MPD control system is presented and results from drilling a well in the Umm al-Quwain region in the UAE demonstrate invaluable benefits for both normal operations and during well control events. Due to its transient nature, drilling has always been a complicated operation and requires highly skilled personnel to achieve the desired pressure control accuracy. The introduction of automated MPD systems tries to implement more robust and safer control over well control operations that were previously manual tasks, however, this is still a challenge since wellbore conditions are constantly changing. This has prompted the need for proactive and model-based control techniques that act in advance to optimize the performance based on measurements and knowledge of the system. The development of this state-of-the-art MPD control system involved detailed validation in a high-fidelity simulator and thorough tests of robustness and performance in a full-scale flow loop with continuous gas injection capabilities, with focus on two-phase flow and gas influx handling. Results from field operations show that the model-based MPD control system maintains robust performance during planned operations such as connections and drilling ahead. Based on pump flow measurements surface back-pressure or bottom hole pressure are maintained constant during fast pump ramp-down and ramp-up without the use of a back-pressure pump. Usually, MPD control systems require strict procedures on pump ramp speed to maintain constant pressure during transient operation. In this paper, the model-based control system implemented is shown to handle irregular pump flow changes and still maintain constant surface back-pressure or bottom hole pressure. In particular, a simulated pump emergency shutdown is shown where the pumps are stopped in less than 20 seconds. The MPD control system still managed to maintain constant bottom hole pressure by closing the chokes in a controlled manner. In summary, this paper presents a field implementation of a fully model-based MPD control system that demonstrates its ability to compensate for irregular pump flow changes. Throughout these irregular pump flow changes, the control system maintains constant bottom hole pressure or surface back-pressure. Furthermore, the system demonstrates the ability to maintain the desired pressure control precision in all normal operations and during all unplanned events experienced during the operation.

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The focus of this paper is on the benefits of model-based control for performance of pressure control and how to enhance robustness against changes in system dynamics by use of adaptive control in managed pressure drilling (MPD) operations. In this work, we present the advantages and disadvantages with adaptive model based control for MPD operations, by implementation of a choke pressure controller. The paper will show that model-based control enables pressure control down to fully closed choke and trapping pressure without a backpressure pump. Moreover, by adding adaption to the model-based controller it is made robust to changing well parameters, recovering control performance. This is part of a pre-study and preparation for flow loop testing in Abu Dhabi Winter 2016, where performance and robustness of the controller is tested for gas influx and a variety of standpipe pump rates and pressure ranges. The purpose of the flow loop testing is to verify that the controller gives satisfactory performance and is the final test stage before the technology is ready for field use.