Chemicals in Gulf Didn’t Stop Oil Rise

Tuesday, December 4, 2012 @ 06:12 PM gHale


Deepwater Horizon disaster is over, but the methods to control the catastrophe are now under review and the dispersant used to help contain the spill remains a hot topic.

As the Deepwater Horizon incident unfolded, in an effort to prevent the oil from coming to the surface and reaching coastal and marsh ecosystems, chemical dispersants ended up injected at the wellhead. These powerful dispersants, typically used to break up oil slicks at the sea surface never saw use before in such large quantities and over such a prolonged period of time in the deep ocean.

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A new study led by University of Miami (UM) Rosenstiel School of Marine & Atmospheric Science Associate Professor of Applied Marine Physics Claire Paris, examined the effects of the use of unprecedented quantities of synthetic dispersants on the distribution of an oil mass in the water column, based on a modeling approach.

A team of researchers developed and tested models that ended up showing the application of oil-dispersing chemicals had little effect on the oil surfacing in the Gulf of Mexico.

“Deepwater drilling into large, high-pressure reservoirs of oil and gas located far offshore and hundreds of meters below the ocean’s surface involves risks for which we were not adequately prepared,” Paris said.

“As the oil gushed uncontrolled into the Gulf, injection of chemical dispersant into the deep ocean may have had little effect because the oil was coming out with such pressure that it was already dispersed in small droplets,” Paris said. “It is impossible to know whether the synthetic dispersant was well mixed with the oil as it was injected. Our models treat both scenarios, and regardless of whether you have the dispersant in the water mixture or not, the amount of oil reaching the sea surface remained relatively unchanged.”

The researchers estimated the distribution of oil droplet sizes with and without injection of dispersant at the wellhead.

They then applied a novel oil-mass tracking model of the Connectivity Modeling System (CMS) developed shortly after the incident and presented a three-dimensional simulation of the spill showing the unfolding of the disaster to examine the effect the synthetic dispersant may have had on the oil transport in the water column.

The model indicated the dispersant injected at BP’s Macondo wellhead was not necessary to break up the oil. The subsea application of dispersant did not have its expected outcome.

“This study is notable because it presents a comprehensive estimate of the Macondo blowout from the microscopic oil-water interface through the macroscopic transport of crude oil.” said team member, chemical engineer and Ph.D. Candidate Zachary Aman from Colorado School of Mines. The work served as a milestone in assessing the three dimensional transport of oil in the water column.

“Since the beginning of the spill our model accurately predicted the decoupling between the surface and subsea oil transport, and was unique in showing the southwest extension of the deep plume,” said team member, physical oceanographer and UM Rosenstiel School Assistant Scientist Matthieu Le Henaff. “Correct assessment of upwelling and downwelling currents for the circulation model created a realistic scenario that we then used to test the effect of the injection of dispersant on the oil partition.”

As global deep-sea oil exploration expands, the model will be helpful in quantifying the utility of synthetic dispersants for deep water oil leaks.

“The CMS oil model was able to predict the strange layering of oxygen deficit anomalies that we observed during our field sampling and provided us a three dimension view of a phenomena that was constantly changing in time,” said team member, biological oceanographer and Research Associate Professor Ajit Subramaniam from Lamont Doherty Earth Observatory at Columbia University. “For us, it was like being able to track the ghosts of the oil plume because the oil itself had been consumed by the microbes and all that was left were the oxygen anomalies and the model was critical for us to understand what we were observing in the field.”



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