The Deepwater Horizon Blowout

Wildlife coated in petroleum, a result of the Deepwater Horizon blowout. Photo Credit: BP America.

The accidental blowout of the Deepwater Horizon (DH) drilling platform off the Gulf coast of Mexico is an unprecedented event that resulted in 83 days of uncontrolled well flow from the Macondo MC252 formation, approximately 4.1-4.4 million barrels of crude oil released, 2.5 x 108 standard m3 of natural gas, and 430 miles of oiled wetland coastline.

Although the full aftermath of this disaster is not yet clear, it will certainly have far reaching environmental and economic impacts. The incident itself emphasizes the critical need for an adaptive spill response system, one that can observe and predict the fate and transport of petroleum fluids in real-time and guide decisions on response and mitigation.

CEE’s Dr. Thorsten Stoesser specializes in computational fluid dynamics, open-channel hydraulics, and environmental fluid mechanics. He is currently working with colleagues at Texas A&M to develop an integrated response system for oil spills in the Gulf of Mexico. This specialized team of researchers, called Gulf Integrated Spill Response Consortium (GISR), is developing nested numerical models that are linked to a multi-faceted observation system to facilitate observation, prediction, and the decision-making sequence during a spill. Through this effort, GISR will address how oil and gas from such spills are transported and how these compounds evolve over time and space within the ocean and coastal environments. The research has the potential to dramatically improve the response, forcasting, and risk assessment of future drilling in the Gulf.

When a blowout occurs, the separating seawater can contain a significant mass of dissolved natural gas and oil. It can also carry a large fraction of liquid oil in the form of small oil droplets. Crossflow-dominated plumes and stratification-dominated plumes are very limiting in terms of the separation that occurs. Scale analysis indicates that the DH plume is stratification-dominated, and observed locations of hydrocarbon intrusion layers agree with the experimentally derived empirical scaling laws. (Texas A&M) The team’s laboratory experiments of multiphase plumes in stratification and crossflow have increased understanding of the physical mechanisms leading to separation among the buoyant dispersed phases (oil and gas) and the entrained and dissolved constituents in the continuous phase. Stationary fluid is set into motion by reaction forces acted by the bubbles, leading to the presence of unsteady vortices and thereby causing oscillations in the rising plume. Figure A shows the position of bubbles with vertical velocity contours. Streamlines of the instantaneous and time-averaged flow field are also plotted. The simulation of multi-phase plumes in uniform crossflow replicates the dispersed liquid (oil) phase in the plume with uniform crossflow. Figure B shows isosurfaces of oil concentration with contours of fluid flow field in the background. The spread of the rising oil plume due to crossflow is clearly visible in
this illustration.

Spill management options must balance methods to reduce shoreline impact with the possibility of generating hypoxic regions in deep waters. This balance requires an ability to predict shoreward transport, subsurface fractionation, and biodegradation of spilled oil and gas, both for planning purposes and more urgently for real-time decision support during an oil spill. The GISR team’s research will serve as a guide for necessary infrastructure to observe oil behavior in an ocean environment, forcast the fate and transport of petroleum fluids, determine accurate response strategies for future spills, quantify the human health risk to such spills, test the efficacy of mitigation strategies, and risk assessment of drilling activities in the Gulf.

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From left to right, laboratory simulation experiments of multiphase plumes in crossflow, indicating (a) stratified plume, and (b) strong crossflow. Streamlines and vectors showing the (L-R) instantaneous; time-averaged flow field in the bubble column; and position of bubbles, along with vertical velocity contours.