Oil droplet size calculation with and without dispersants in an underwater well blowout

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Poojitha Yapa, Indrajith Nissanka

Thursday 2 july 2015

14:25 - 14:40h at Europe 1 (level 0)

Themes: (T) Special session, (ST) Oil spill modelling

Parallel session: 12J. Special session: Oli Spill Modelling

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In an accidental underwater oil well blowout, the major concerns of emergency response and contingency planning are to predict the amount of oil that reaches the surface, how fast it reaches the surface, and the surface spreading. In this regards, oil droplet sizes play a critical role, as the rise velocities of droplets essentially depend on their size although non-linearly related due to a variety of factors including the changes in shape. Therefore, accurate calculation of droplet size distribution is very important in modeling and predicting the fate and transport of oil in the water column and surface spreading. However, the current knowledge on oil droplet size calculation/estimation is limited with only a few methods available. None of the above methods are robust enough to calculate different droplet sizes corresponding to wide ranges of release conditions. Further, the theoretical knowledge behind the computation of small droplet sizes is almost none in existing methods. In this paper we introduce an improved theoretical method starting with Bandara and Yapa (2011) to calculate droplet sizes for a wide range of underwater accidental oil releases. Droplet evolution is modeled using population balance equation. Here, we consider the oil droplet break up and coalescence as death and birth of droplet sizes. This results in 4 primary components that had to be computed separately together to find the final distribution. In computing these components we use new improved methods for energy dissipation, droplet breakup rate and coalescence rate closures. The new model is validated with experimental data from Deepspill field experiments and a series of recent experiments conducted by SINTEF (Brandvik et al., 2013) which include cases with and without dispersants. The model results show a very good agreement with experimental data for without dispersants cases and with dispersants cases model calculations show reasonable initial results with good promise for continuation of the work. This work is still progressing.