Disturbance Attenuation in Managed Pressure Drilling Using Impedance Matching and an Experimental Lab Setup
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Due to often harsh weather conditions and great water depths, the offshore drilling industry faces many challenges. One of these challenges is to counteract surge and swab pressure effects in the drilling well caused by the vertical motion of a floating drill rig. If the pressure in the annulus is kept within safe limits, it may allow us to drill wells previously regarded as undrillable, or permit further extraction of hydrocarbons from depleted reservoirs. Managed pressure drilling consists of a set of techniques that may aid us in limiting the bottomhole pressure fluctuations. By installing a choke and a backpressure pump, one may be able to get more control of the bottomhole pressure during connections, when the active heave compensators of the drill rig are disabled, and the drill string is extended.This thesis focuses on impedance matching as a means of reducing surge and swab pressures caused by heave motions. For this, an experimental lab setup has been used. The lab setup is intended to resemble a real drilling rig setup during connections. With the help of a submersed piston as well as a choke and a backpressure pump, the lab may enable us to test out various ways of reducing surge and swab pressure fluctuations. A wide variety of sensors allows us to measure pressures and flows at several locations in the rig. The experimental frequency responses of the lab setup are found for various constant choke angles. These frequency responses are in turn used to formulate an optimization problem in order to find an ideal choke opening to reduce the bottomhole pressure fluctuations caused by heave motions.