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| 3D reconstruction of a hydrocarbon jet leaking from the Deepwater Horizon's broken riser. Each colored dot represents the location of an acoustic Doppler velocity measurement, with the dot color describing the velocity. The black ellipse indicates the size and location of the jet source; blue dashed ellipses indicate the jet flow perimeter. Black dots indicate the position of the ROV-mounted Doppler sonar during the measurement sequence. (Illustration courtesy of Rich Camilli, Woods Hole Oceanographic Institution) Enlarge Image |
The results—published in the Sept. 5, 2011 online issue of the Proceedings of the National Academy of Sciences (PNAS)—are in line with the federal government’s official estimates, but just as importantly validate the innovative measuring techniques the team employed. The accuracy of the measurements was crucial because, “Ultimately, the impact of the oil on the environment depends primarily on the total volume of oil released,” according to a report by the Flow Rate Technical Group (FRTG), a collection of research teams charged with using different means to generate an accurate estimate of the amount of oil released into the Gulf.
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| Dark fluids containing oil and natural gas gush out of the broken riser pipe at the Macondo well near the seafloor in the Gulf of Mexico in 2010. Officials needed an accurate measurement of how much oil was flowing out. (Photo courtesy of U.S. Geological Survey) Enlarge Image |
On May 19, 2010, prior to commencing investigation of the Deepwater Horizon leak, Camilli testified to Congress that this proposed acoustic measurement technique would be capable of quantifying the flow rate to within “a factor of two.” The WHOI-led team found just a 17% uncertainty, or error, associated with their estimate.
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| The scientists needed to distinguish how much oil versus gas was leaking from the well. To collect and analyze the well fluid itself, WHOI scientists used an isobaric gas-tight sampler, or IGT, a deep-sea device developed at WHOI to sample hydrothermal vent fluids. A pristine fluid sample from within the well was crucial to understand what fraction of the flow was oil. The manipulator arm of a robotic vehicle (upper right) moves the IGT sampler toward the jet of hot oil and gas shooting out of the broken drill pipe. (Photo courtesy of Oceaneering) Enlarge Image |
That low uncertainty rate was due, in large part, to the team’s pioneering measuring techniques, devised primarily by Camilli and WHOI colleague Andrew Bowen. In late May of 2010, the WHOI team installed two acoustic instruments on a remotely operated vehicle called Maxx3. The first was an acoustic Doppler current profiler or ADCP, which measures the Doppler shift in sound, such as the change from the higher pitch of a car as it approaches to a lower pitch as it moves away.
“We aimed (the ADCP) at the jet of oil.and gas that was coming out, and based on the frequency change in the echoes that came back from the jet, we could tell just how fast it was moving,” said Camilli. Within minutes, they obtained more than 85,000 Doppler measurements.
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| Lead scientist Richard Camilli is taken by helicopter to Deepwater Horizon site to perform measurements. (Photo by Andy Bowen, Woods Hole Oceanographic Institution) Enlarge Image |
“By using the acoustic techniques, we were able to collect a tremendous amount of data in the limited time window that was available,” Camilli said. “We were able to see inside of the flow and make measurements of the velocities. With optical systems, you see only the outside. This was sort of like x-ray vision.”
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| Andy Bowen, director of the National Deep Submergence Facility at WHOI, works with the remotely operated vehicle Maxx3, which carried acoustic sensors to the measure the rate of oil flowing out of the at the blown-out Macondo well drill pipe. (Photo courtesy of Andy Bowen, Woods Hole Oceanographic Institution) Enlarge Image |
While working at the disaster site, Camilli set up a satellite link with a team of researchers throughout the country to meticulously analyze the data. Using computer models of turbulent jet flow, they came up with an estimate of how fast the fluids were flowing out of the pipe.
To collect and analyze the well fluid itself, WHOI used an isobaric gas-tight sampler, or IGT, a deep-sea device developed at WHOI to sample hydrothermal vent fluids. A pristine fluid sample from within the well was crucial to understand what fraction of the flow was oil.
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| Photograph of a hydrocarbon jet leaking from the Deepwater Horizon's broken riser (Photo by Rich Camilli, Woods Hole Oceanographic Institution) Enlarge Image |
An accurate flow rate gave engineers a clearer picture of what was happening below the surface and a better chance of figuring out how to stem the flow, how much dispersant should be applied to prevent oil from reaching the surface, and to map strategies to regain control of the well, collect the oil, and limit the environmental damage.
Of the nearly 5 million-barrel total of oil released, an estimated 800,000 were recaptured directly from the well by containment measures and never reached the environment, according to the FRTG report.
Unlike most oil spills in the ocean, which occur at or near the surface, this one was happening nearly a mile deep. It had not been known exactly how petroleum released under the intense pressure and cold temperatures in the depths would behave chemically or physically, but many suspected that not all of it would make it to the surface. “No proven techniques existed for estimating the flow under such conditions,” said an FRTG report dated March 11, 2011.
“Over the past decade ultra deepwater oil platforms have gone from non-existent to representing about 1/3 of the Gulf of Mexico’s oil production and plans call for a growing number of such facilities,” Camilli said. “Society benefits when industry, government, and academia work cooperatively to improve assessment and intervention capabilities” in that setting. The new study confirms “a new tool in the repertoire” to monitor ultra deepwater facilities, he added.
Reddy concurred. “If there is any silver lining” to the Deepwater Horizon spill, he said, “it’s that the techniques and equipment developed and used by [Camilli and Bowen] could be used in the future” to help monitor and control any problems with deep-water oil facilities.
Other WHOI members of the research team include Dana R. Yoerger, Jeffrey S. Seewald, Sean P. Silva, Judith Fenwick and Louis L. Whitcomb (also of Johns Hopkins University); along with Daniela Di Iorio of the University of Georgia, and Alexandra H. Techet of MIT.
The study was funded by the U.S. Coast Guard with additional support from a National Science Foundation RAPID grant and the WHOI Coastal Ocean Institute.
The Woods Hole Oceanographic Institution (WHOI) is a private, nonprofit research and higher education facility dedicated to the study of all aspects of marine science and engineering and to the education of marine researchers. Established in 1930, it is the largest independent oceanographic research institution in the U.S., with staff and students numbering about 1,000. The Institution is organized into five departments, four interdisciplinary institutes—ocean life, coastal ocean, ocean and climate change, deep ocean exploration—the Cooperative Institute for Climate and Ocean Research, and a marine policy center. Its shore-based facilities are located in the village of Woods Hole, Massachusetts, and a mile and a half away on the Quissett Campus. The bulk of the Institution's funding comes from grants and contracts from the National Science Foundation and other government agencies, augmented by foundations and private donations.
