A comprehensive deepwater well control system for riser gas unloading mitigation




Gu, Qifan

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Offshore hydrocarbon production has been growing extensively since the 1960s. However, today, most of the “easy” offshore hydrocarbon plays at shallower water depths appear to have been found, and operating companies are turning progressively to exploration and production in deeper water for new hydrocarbon plays. Due to the higher costs, risks and uncertainties that come with increased water depth, various drilling techniques have been developed and implemented in deepwater wells to improve safety and efficiency. Managed pressure drilling (MPD) is one of the most effective techniques, with capabilities to mitigate drilling hazards and reduce non-productive drilling time. However, the current MPD techniques can still be significantly improved with better hydraulics models considering deepwater drilling realities, and better detection and control algorithms that cover specific deepwater drilling events such as riser gas unloading. In this Ph.D. dissertation, studies and methods will be presented to improve well control techniques, and specifically MPD-related well control techniques, in deepwater drilling. A drift-flux model that considers temperature dynamics and the liquid-gas mixture realities in deepwater environments will be first derived for evaluation purposes. A reduced drift-flux model will be derived thereafter for real-time estimation purposes, which shows advancements compared to the historical models by improving the pressure / temperature dynamics calculation and considering gas solubility behavior. An event detection system will then be introduced, using real-time streaming data to detect the occurrence of relevant events and to classify their type. Finally, a control system that includes a pressured riser drilling controller and a novel control strategy will be presented, which provides a safer and faster solution for deepwater kick events. The work in this dissertation aims to open up the possibility of new approaches to achieving deepwater well control for riser gas unloading mitigation (RGUM) that will improve rig safety and are more efficient (in terms of time and cost) at the same time. In addition to RGUM, it also aims to help facilitate the general implementation of advanced automatic solutions with lower safety risks for deepwater drilling operations in the foreseeable future


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