Lab for heave motion during Managed Pressure Drilling
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A significant part of the world's remaining oil and gas prospects are challenging or impossible to reach by conventional methods. Examples are deep-water environments and depleted reservoirs with a narrow drilling window, requiering a more accurate control of the downhole pressure to be able to conduct the drilling operation as safe and efficient as possible. The Constant Bottomhole Pressure (CBHP) variation of Managed Pressure Drilling (MPD) addresses the challenges of drilling within a narrow drilling window by controlling the wellbore pressure by use of backpressure from surface and a choke manifold. It has been applied both onshore and offshore, but mainly from fixed platforms in offshore environment. However, some applications have been run also from floating drilling rigs in calm waters, whereas no MPD solution is available for North Sea conditions with severe heave motions. This thesis addresses the challenges of downhole pressure fluctuations related to heave motion when drilling from a floating rig in rough environments during connections. By reconstructing such conditions in lab scale, a new developed control algorithm is to be tested to reduce the downhole pressure variations as much as possible. It is desired to obtain new information to continue the research and to come up with a solution for heave compensation during MPD floating rigs. This thesis presents the design of the MPD Heave Rig and functional specification of the components in the lab scaled model. The purpose of the model is to simulate the heave motion by moving a pipe up and down in a hole to obtain pressure fluctuations in the hole and apply a control system which controls these pressure variations based on the principles of constant bottomhole pressure MPD. By use of a water pump and a choke, the pressure variations in the hole are compensated for by adjusting the choke opening. A 900 meter long copper pipe is implemented in the model to simulate the time delay of a pressure transient traveling from the surface to the bottom of the well. A tailored system for the choke to be controlled by the control system has been developed and tested for a temporary prediction of the choke characteristics. A plan for further testing of technical components and parameters for the hydraulic model is presented for future work with the rig. It has been conducted a risk assessment considering the whole process of building, testing and running experiments. Measures are implemented and suggested to ensure operational and technical safety of people and equipment involved in the MPD Heave Rig project.