Direct coupling of near-field and far-field models hones predictions of oil spill transport and fate from deep-sea blowout

Deep-water spills pose a unique challenge for reliable predictions of oil transport and fate, since live oil spewing out under very high hydrostatic pressure has characteristics remarkably distinct from oil spilling in shallow water. It is thus important to describe the complex thermodynamic processes occurring in the near-field, meters above the wellhead, and the hydrodynamic processes in the far field, up to kilometers away. However, these processes are typically modeled separately since they occur at different scales. Here we directly couple two oil prediction applications developed during the Deepwater Horizon blowout operating at different scales: the near-field Texas A&M Oilspill Calculator (TAMOC) and the far field oil application of the Connectivity Modeling System (oil-CMS). To achieve this coupling, new oil-CMS modules were developed to read TAMOC output, which consists of the description of distinct oil droplet “types”, each of specific size and pseudo-component mixture that enters at a given mass flow rate, time and position into the far field. These variables are transformed for use in the individual-based framework of oil-CMS, where each droplet type fits into a droplet size distribution (DSD). Here we used 19 pseudo-components representing a large range of hydrocarbon compounds and their respective thermodynamic properties. Simulation results show that the dispersion pathway for different droplet types varies significantly. Indeed, some droplet types are predicted to remain suspended in the subsea over months, while others accumulate in the surface layers. In addition, the biodegradation and dissolution rates of oil pseudo-components significantly alter the dispersion, denoting the importance of more biodegradation and dissolution studies of dispersed live oil at high pressure, with and without subsea dispersant injection (SSDI). This new modeling tool shows the potential for improved accuracy in predictions of oil partition in the water column, and of advancing impact assessment and response during a deep water spills.