MIAMI, Fla. (April 1, 2015)—In a first-of-its-kind study, researchers from the Rosenstiel School of Marine and Atmospheric Science and the University of Western Australia observed how oil droplets are formed and measured their size under high pressure. Simulating how atomized oil spewing from the Macondo well during the Deepwater Horizon accident reached the ocean’s surface, they suggest that the physical properties of deep water create a natural dispersion mechanism for oil droplets similar to the application of chemical dispersants at the source of an oil spill.
“These results support our initial modeling work that the use of toxic dispersants at depth should not be a systematic oil spill response,” said UM’s Claire Paris, associate professor of ocean sciences. “It could very well be unnecessary in some cases.”
The research team from the Center for the Integrated Modeling and Analysis of the Gulf Ecosystem, or C-IMAGE, conducted eight experiments to simulate different pressures of oil from a blowout at depth. The oil was placed in a high-pressure chamber, called a sapphire autoclave, and monitored using a high-speed, high-resolution camera to evaluate how droplets form at varying turbulent conditions.
“This is the first time that we’ve been able to visually monitor how droplets break up and coalesce at up to 120 times atmospheric pressure,” said Zachary Aman, associate professor of mechanical and chemical engineering at the University of Western Australia. “When paired with the high pressures and flow rates of Macondo, the results suggest a natural mechanism by which oil is dispersed into small droplets.”
The results of the laboratory experiment were applied in a field-scale simulation under the same physical conditions that existed during the Macondo well blowout. In the computer simulation, the team tracked the oil released at a constant rate of 1,000 oil droplets every two hours at a depth of 300 meters above the Macondo well, corresponding to the depth of the observed deep plume, from April 20 to July 15, 2010, when the Macondo well was capped; droplets were tracked for an additional 24 days after the cap was in place.
Based on the experimental data and modelling, the researchers suggest that the use of chemical dispersants may have reduced the mean oil droplet diameter from about 80 to 45 micrometers, which would have reduced the amount of oil reaching the surface only by up to 3 percent. The model simulations showed that if the blowout occurred in shallow water conditions, or at a smaller rate of hydrocarbon release, dispersant may have had a more significant impact on the oil flowing from the well.
Already available online, the research paper, titled “High-pressure visual experimental studies of oil-in-water dispersion droplet size,” will be published in the May 4 edition of the journal Chemical Engineering Science. In addition to Paris and Aman, the coauthors include David Lindo-Atichati of the UM Rosenstiel School, and Eric F. May and Michael L. Johns of the University of Western Australia.