Disturbance Attenuation in Managed Pressure Drilling

Abstract

In reservoirs where multiple wells have been drilled, the window that the pressure has to stay within becomes smaller. This calls for tight control of the pressure profile in the well. An extra challenge is provided when drilling from a floating rig: The Heave motion. During normal operation the heave motion is compensated for. However, when the drillstring needs to be extended it is connected to the rig, which causes it to move with the rig. This creates huge pressure fluctuations in the well. Multiple papers have been written on the subject of suppressing these fluctuations. An experimental lab has been built at NTNU to model this scenario, called the IPT-Heave Lab. The goal of the lab is to have a realistic test environment for the developed controllers and be able to test new control algorithms.This thesis has concerned itself with making the IPT-Heave Lab operational. The scenario the lab is built for is the use of a technique called constant bottomhole pressure to suppress the heave motion. With this technique a choke is used to control the pressure at the top of the well. In this thesis a controller for the choke is developed, and its performance has been demonstrated in the lab. Furthermore motivated by literature study, a model of the lab has been identified based on a black box modeling principle. The identified model has then been used to design an MPC-controller. The MPC-controller has been demonstrated to suppress disturbances, simplified to a single sine wave, of a period of 3 seconds by approximately 46 %.