Modeling homogeneous and heterogeneous aggregation and breakup processes for oil/gas spills. (i) Oil and gas bubbles in deepwater blowouts. (ii) Oil-sediment interaction

Bubble size distribution (BSD) plays a major role in the transport and fate of gas or oil released in deepwater. However, no reliable method is available to estimate gas or oil BSDs after a deepwater spill. Breakup and coalescence processes have been identified as key mechanisms controlling BSD in turbulent jets. This thesis introduces bubble breakup and coalescence processes for deepwater gas or oil spill models. Population balance equation representing bubble volumes is used to model the evolution of bubble sizes due to breakup and coalescence. Existing theories for bubble breakup and coalescence rates in variety of industries are adopted to deepwater plumes. The advantage of the present model is that the BSD is generated as a result of breakup and coalescence and therefore, a predefined BSD is no longer necessary for simulations. The numerical model is tested against the available data from laboratory and field experiments. Experimental data by Hesketh et al. (1991), Masutani and Adams (2001), and Johansen et al. (2000) are compared with the model results. In all the cases model results compare well with the experimental data. Scenario simulations showed that the seed diameter given to start computations impacts only within a short distance after the release. Simulations further showed that bubble breakup and coalescence is important only during the early stages of the plume.;Spilled oil, when present in regions with high suspended sediment concentrations such as estuaries, is known to interact with sediments. Oil droplets can form aggregates with sediments due to collision and dissolved oil can be absorbed into sediments. This may change the fate and transport of both oil and sediments. Oil interacting with sediments acts as a natural oil removal process after an oil spill. Although this has been recognized as an important process in developing oil spill countermeasures, comprehensive models are not available to describe the process. This thesis further presents a novel numerical model developed to simulate oil-sediment interaction and transport in near-shore waters. The model simulates, oil-sediment transport, oil-sediment aggregate formation, oil partitioning into sediments, and sediment flocculation. The model is tested against the limited data from laboratory experiments. Scenario simulations showed that when oil droplets and sediment particle sizes are smaller, the amount of oil-sediment formed is high. They further showed that the amount of oil partitioned into sediments is 4-5 orders of magnitude smaller than the amount of oil-sediment aggregates.