Modeling Study Suggests Dispersants Used at Wellhead had Marginal Effect on Oil Reaching Surface Waters

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Simulated 3D spatial distribution of oil products below the surface based on current advection and oil buoyancy in the region. The formation of the prominent deep hydrocarbon intrusion (blue plume) and the layering of shallower plumes (cyan and green) indicate that chemical dispersants injected at the wellhead were likely not effective in changing the amount of oil reaching the surface. The oil in the top 20 m of the sea surface is not shown.

(Click to enlarge) Simulated 3D spatial distribution of oil products below the surface based on current advection and oil buoyancy in the region. The formation of the prominent deep hydrocarbon intrusion (blue plume) and the layering of shallower plumes (cyan and green) indicate that chemical dispersants injected at the wellhead were likely not effective in changing the amount of oil reaching the surface. The oil in the top 20 m of the sea surface is not shown.

Scientists studying the use of sub-sea chemical dispersants during the Deepwater Horizon spill published their recent findings in the November 2012 issue of Environmental Science and TechnologyEvolution of the Macondo well blowout:  Simulating the effects of the circulation and synthetic dispersants on the subsea oil transport.

While oil was flowing into the Gulf of Mexico, responders injected chemical dispersants at the Macondo wellhead to reduce the amount of oil from surfacing and impacting coastal and marsh areas. The authors used a novel oil-mass tracking model (the Connectivity Modeling System) to simulate in three dimensions the oil discharge in deep waters and examine the effect that a deep water release of oil, with and without dispersants, may have had on the oil droplet size and transport through the water column.  By studying a wide range of contributing factors, researchers found that the amount of oil reaching the sea surface may have been the same independent of dispersant application. Based on fundamental oil droplet size models, the authors estimate that the turbulent discharge of oil resulted in naturally small droplets contributing to the observed deep intrusion. The numerical experiments also suggested that the large fraction of gas may have caused the initial rapid surfacing of oil, due to an increase in overall buoyancy. This study revealed previously undocumented temporal aspects of the oil in the water column moved by local topographic and hydrodynamic processes. The authors’ numerical approach provides new insights on oil transport from deep blowouts and on future subsea use of dispersant in efforts to mitigate coastal damage.

Graph shows percent oil mass differences without surfactant where positive anomalies (red) indicate more oil and negative anomalies (blue) indicate less oil. The oil mass represented by the lower size fraction between 1-70 μm, is less localized below 1200 m, while more diffuse in the water column up to 600m below the surface without the synthetic dispersant. The magenta line marks the capping of Macondo well on July 14th, 2010.

(Click to enlarge) Graph shows percent oil mass differences without surfactant where positive anomalies (red) indicate more oil and negative anomalies (blue) indicate less oil. The oil mass represented by the lower size fraction between 1-70 μm, is less localized below 1200 m, while more diffuse in the water column up to 600m below the surface without the synthetic dispersant. The magenta line marks the capping of Macondo well on July 14th, 2010.

The study authors are Claire B. Paris, Matthieu Le Hénaff, Zachary M. Aman, Ajit Subramaniam, Judith Helgers, Dong-Ping Wang, Vassiliki H. Kourafalou, and Ashwanth Srinivasan (Environmental Science & Technology 2012 46 (24), 13293-13302).

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This research was made possible in part by grants from BP/The Gulf of Mexico Research Initiative through the C-IMAGE and Deep-C consortia. Other funding sources included the National Science Foundation RAPID OCE-10- 48697 to C.B.P.; RAPID OCE-10-48482 and OCE-10- 58233 to A.S. for observations.

The GoMRI is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies.  An independent and academic 20-member Research Board makes the funding and research direction decisions to ensure the intellectual quality, effectiveness and academic independence of the GoMRI research.  All research data, findings and publications will be made publicly available.  The program was established through a $500 million financial commitment from BP.  For more information, visit http://gulfresearchinitiative.org/.

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