The subsurface plume from the Deepwater Horizon (DH) accidental oil-well blowout is a complex, layered system of intrusions containing oil, dissolved hydrocarbons, and injected dispersants that will have far-reaching environmental consequences; however, no modeling tools are currently producing highly-resolved predictions of the plume structure and evolution. The goal of this Rapid Response Research Proposal (RAPID) is to develop a three-dimensional, multiscale hydrodynamic model for the DH blowout plume that combines the Reynolds averaged Navier Stokes (RANS) modeling approach with the method of large-eddy simulation (LES). The resulting model platform will be validated to field and laboratory data, will respect the relevant chemistry and thermodynamics of the released oil and natural gas, and will be forced by the measured ambient conditions surrounding the spill. Such a simulation tool is urgently needed to guide field observations, predict the onshore migration and loop-current capture of the spilled oil, assess the effectiveness and potential environment impact of dispersants injected at the source, and to understand the response to this event already measured in the vertical migration of plankton and fish. The validated modeling platform will be developed through complementary laboratory experiments, numerical modeling, and analysis of field data. The laboratory experiments will evaluate the effects of currents as the flow through the plume and pull oil and dissolved constituents into the wake of the plume. The numerical methods will utilize a very large eddy simulation (VLES) to resolve the dominant plume structures in the near field of the blowout plume and will nest this model in a far-field model based on the unsteady RANS approach. Field data from acoustic Doppler current profilers will provide model forcing and validation data and will also be analyzed to understand the role of subsurface plume dynamics on the vertical migration of plankton and fish as also recorded in the ADCP data. Early analysis of this data shows a very rapid shut-down of the diurnal vertical migration pattern at nearby stations shortly after the start of the spill. This is the first documented environmental response to the blowout, and it remains unknown whether this is due to mortality, avoidance, light penetration changes or other processes. The sub-surface plume model developed here will provide detailed predictions of the subsurface plume structure necessary to analyze this environmental response.
Intellectual Merit: The primary intellectual merit of the project will be an understanding of the critical physical and chemical processes in an accidental oil-well blowout that lead to the subsurface layered structure of oil and dissolved hydrocarbons in the water column. Important insight will also be gained on the appropriateness of a classical RANS model for predicting the dynamics of the oil and gas intrusions. Broader Impact: Predictions from the model will help guide the collection of observation data in the field and will be applied to understand why plankton and fish in the vicinity of the blowout shut down their vertical migration pattern shortly after the blowout. The model is also needed to predict the transport of oil and injected dispersants throughout the Gulf ecosystem, including onshore and into the loop current and potentially into the Atlantic ocean. Detailed studies of turbulence in multiphase plumes conducted in the later stages of the project will ultimately result in a reliable model framework featuring a zonal RANS-VLES simulation tool applicable to a wide range of environmental applications of multiphase plumes, including CO2 sequestration, lake aeration, and sediment plumes, among others.
This project conducted new laboratory experiments to provide data to validate computer models for deepwater accidental oil well blowouts. Research staff also retrieved field data for velocity, backscatter, and oil presence from publically available data sources. New laboratory experiments were conducted using the particle image velocimetry (PIV) method for two-phase (air bubble) plumes in a uniform current. The experiments span a similar parameter space as reported in Socolofsky and Adams (2002, J. Hydr. Res., 40, 6), but add quantification of the flow field upstream, through, and downstream of the bubble column to the qualitative observations in Socolofsky and Adams (2002). The experiments were conducted using a high speed Phantom camera in order to track individual turbulent coherent structures through the flow field. Analysis of the data provides streamlines of the flow field, average velocity vectors, turbulent kinetic energy maps, maps of Reynolds stresses, and entrainment and detrainment fluxes to the plume. These data are important for development and validation of new modeling tools for multiphase plumes in crossflow. Analytical models originally presented in Socolofsky and Adams (2003, J. Hydr. Eng., 129, 11; 2005, J. Hydr. Eng., 131, 4) were adapted to study the near-field plume behavior of the Deepwater Horizon accident. The equations were modified to account for the local nonlinear density stratification in the Gulf of Mexico deepwater, and results of the predictions were validated against CTD profile data that included fluorescence measurements indicating where dissolved and liquid oil intruded into the water column. The results of these activities were summarized in a journal article, published as Socolofsky, Adams, and Sherwood (2011, Geophys. Res. Lett., 38, L09602). This article explains the origin of subsurface oil intrusions for the Deepwater Horizon accident and attributes them to intrusions forced by density stratification of the seawater. Due to the high profile of the Deepwater Horizon accident, several news agencies are interested in the results of this project. The PI has given phone interviews to the Boston Globe, email interviews to National Public Radio (NPR), and collaborated with NSF on the CBET National Geographic Project 2011. These activities have focused on the near field plume physics and how subsurface intrusions of oil and dissolved hydrocarbons formed in the deep Gulf of Mexico from the Macondo spill. The PI has also given invited seminars on the Deepwater Horizon blowout and the work summarized here at Texas A&M University, the University of Texas at San Antonio, the University of California at Berkeley, and at Virginia Tech. In addition, the PI, along with Eric Adams of the Massachusetts Institute of Technology and Steve Masutani of the University of Hawaii were honored by receiving the IgNobel Prize in Chemistry for their previous work on deepwater accidental oil well blowouts. This award afforded the opportunity to give public lectures on subsea oil well blowouts; some of these lectures were aired on NPR’s Science Friday during the week of Thanksgiving, 2010.
