CFD Simulations of Heave-Induced Pressure Oscillations in a Drilling System

Abstract

Managed pressure drilling is an advanced collection of techniques to enhance annular pressure control. During offshore drilling, the heave motion of the rig causes large surge and swab pressure variations down the hole. These oscillations must be counteracted to ensure safe and efficient drilling operations and automatic control systems are developed to attenuate the heave disturbance. Such systems heavily rely on available information about the well, as they often utilize hydraulic models to estimate the pressure variations or controllers that have to be carefully tuned to succesfully control the annular pressure. There are a lot of uncertainties about the bottomhole pressure induced by the heave motion, which reduces the accuracy of the models used for estimation and control of the bottomhole pressure

This thesis focuses on computational fluid dynamics as a mean to predict the downhole pressure variations. A model based on a continous circulation system is created in COMSOL Multiphysics to study the effect of vertical drillstring movement. The bottomhole pressure variations are succesfully predicted when the drillstring is subjected to a simple harmonic motion, and the results are showing relatively large fluctuations compared to the static circulation scenario.