Modelling the Effect of Continuous Circulation on Downhole Pressure Oscillations Caused by Rig Heaving
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In the oil and gas industry a new technology known as Managed Pressure Drilling (MPD)is emerging, allowing for faster and more accurate well pressure control. MPD differsfrom conventional drilling methods by closing the well using a controlled choke, often incombination with a backpressure pump allowing for automatic pressure control. Whenthe drill string is extended the pipe is typically sealed of and detached from the MPDsystem. This process is time consuming and limits pressure control, because the mudflow is stopped. The Continuous Circulation System was developed to allow for betterpressure control during connections and reducing connection time. For these technologiesto become viable for use on floating rigs advanced control algorithms are necessary. Tobe able to test such system simulators are necessary. In this thesis a transmission linecontaining the mud column in the pipe and the annulus coupled through an elastic pipe ispresented in the frequency domain. A set of Robin boundary conditions representing CCSis developed and coupled with a pressure node. A Ritz approximation is developed in orderto discretize the transmission line, and the Laguerre-Gram model order reduction methodis applied to obtain rational transfer function approximation. Some likely numerical issuesare discussed with this method.