Numerical study of the effects of chemical dispersant on oil transport from an idealized underwater blowout

As part of the response efforts that followed the Deepwater Horizon oil spill event, chemical dispersants were applied at the ocean surface and at the wellhead to increase biodegradation rates and reduce the environmental impact of the spill. Among other factors, the effectiveness of the application hinges on how it modifies complex fluid mechanical transport processes. The breakup of surface slicks and the vertical dilution of oil in the water column depends on the transport of oil droplets by turbulence in the ocean mixed layer. The trapping of oil deep in the water column results from the complex dynamics of multiphase plumes rising in the stratified ocean. We use a framework based on multiscale coupled computational domains to simulate deep-water blowouts that accurately represents these complex processes, tracking the oil from the wellhead to its transport in the ocean mixed layer. Simulation results show that dispersant application at the wellhead can be effective in trapping the oil in deep-water intrusions. For the conditions simulated here, surface application of the dispersant has important effects on the oil transport: after about 40 h, the mean advection velocity of the oil plume is reduced by a factor of four and the horizontal diffusivity is increased by a factor of 10.