System Identification and Simulation of an Experimental Setup for Managed Pressure Drilling

Abstract

This thesis looks at the development of a simulator for a lab setup related to heave-related issues in MPD (Managed Pressure Drilling) The aim of the lab is to create an environment for developing control methods to attenuate the pressure fluctuations generated by heave motion. The simulator is based on quasi-linear incompressible 1D pipe equations. The equations are simulated by decoupling and rewriting in terms of Riemann-invariants. The simulator parameters are discussed, and theoretical results are compared to experimental ones from the lab. The simulator is tuned by fitting the frequency response of the bottom hole pressure to the lab's. The wave speed of the simulator needs to be reduced significantly to align the resonance peaks with the frequencies found in experiments. Reasons for discrepancies between the lab and the model are discussed. The programming language used is C, through C-MEX functions for better runtimes. The simulator accuracy is satisfactory for disturbance frequencies up to about 0.25 Hz. For higher frequencies, the steady flow simplification used in the choke equation fails. A distributed observer is implemented within the same framework and is tested on data from the lab. The observer produces accurate estimates for low-frequency disturbances, but with a small phase lag.