LARGE-EDDY SIMULATION OF DEEP-WATER HYDROCARBON PLUME DYNAMICS

During a deep-water wellhead blowout incident, the dynamics of the released hydrocarbon plume is strongly affected by the gas dissolution and hydration process that weakens the bubble-induced buoyancy for driving the plume. In this study, a new modeling strategy is developed to efficiently incorporate the gas dissolution and hydration effects into a fast Eulerian-Eulerian large-eddy simulation (LES) model. By simultaneously simulating the evolutions of the bubble mass concentration and number density functions, the average bubble size in each LES computational cell can be calculated locally. Based on the cell-averaged bubble diameter, the local gas dissolution rate and hydrate formation/decomposition rate and bubble rise velocity are parameterized, which are then used in the gas transport equations to model the evolution of the gas bubble field due to turbulent transport and gas dissolution and hydrate formation and decomposition. In Chapter 2, the LES model is applied to simulate several blowout scenarios with different initial bubble sizes. The results show that the plumes that have smaller initial bubble sizes exhibit a faster relative bubble dissolution rate compared to the plumes with larger initial bubble sizes. As a result, the plumes with smaller bubbles also have lower peel and trap heights than those with larger bubbles. For comparison, a set of cases without including the gas dissolution is also performed. In Chapter 3, a multi-component gas dissolution model is implemented to study the contribution of dissolution from each component and the distribution of dissolved gas in each component. The results show the dissolution ratio for each gas component is different and the average dissolved gas are distributed at different altitude. In Chapter 4, the hydrate formation and decomposition effect are considered in the LES model for hydrocarbon plumes with deeper release conditions. When the gas bubble is released under the equilibrium depth, the gas bubbles and ambient water compose the hydration shell surrounding the bubble surface under deep ocean conditions as well as the gas dissolution into the surrounding seawater and loses its upward buoyancy force throughout the plume's ascent. As the hydrates rise, the hydrates will dehydrate slowly and dissolve into ambient water.