Development and Field Application of a Flow Pattern Dependent Gas Hydrate Kinetics and Transportability Model for Transient Multiphase Flow

Abstract

Oil and gas flowlines operating in subsea or cold terrestrial environments face a heightened risk of forming gas hydrate deposits and plugs after shut-in and during restart, due to the lack of heat supplied from warm produced fluids. Such transient multiphase flow scenarios are not only correlated with increased risk of gas hydrate plugging but are simultaneously the least well-understood gas hydrate risk situation. Gas hydrate plugs are costly to remediate and can result in significant operational downtimes, and they pose potential environmental and safety concerns. As the industry aims to transition from a gas hydrate prevention approach to a gas hydrate management paradigm, it is important to understand the implications of operational actions on gas hydrate formation and plugging risk. This work advances the development of a conceptual picture for gas hydrate formation and transportability in transient multiphase flow scenarios based on laboratory and field observations. A novel gas hydrate kinetics and transportability model has been developed based on this conceptual picture and coupled with a transient multiphase flow simulator. The model makes advancements based on the novel implementation of key physical phenomena that are not well described in existing hydrate kinetics and transportability models, including the impact of intermittent flow patterns on hydrate formation kinetics, transportation of a hydrate slurry via an empirical correlation, and hydrate deposit sloughing. The model has been applied to a transient field case in which a gas hydrate blockage was formed. The model is and was able to predict the formation of gas hydrate plugs in the line and accurately model the associated pressure drop in terms of magnitude, timing, and trend.