The BP Deepwater Horizon oil rig ablaze. Oil spill picture. Image: U.S. Coast Guard.
Looking Back on an Environmental TragedyIt's been more than a year since the Deepwater Horizon oil rig blew up, releasing vast quantities of crude oil and natural gas into the Gulf of Mexico, but we're still trying to figure out exactly how much damage was done. A new study by the Woods Hole Oceanographic Institution (WHOI) estimates that "the blown-out Macondo well spewed oil at a rate of about 57,000 barrels a day, totaling nearly 5 million barrels of oil released from the well between April 20 and July 15, 2010, when the leak was capped."
Picture of the oil gushing from the riser pipe on the sea floor, almost 5,000 feet down below the Gulf of Mexico. Image: BP
"Analysis of the sample showed that, by mass, the Macondo well fluid contained 77 percent oil, 22 percent natural gas, and less than one percent other gases. [...] 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."
The goal of the study was partly to validate the measuring methods pioneered during the spill, to find out if the were accurate and thus, if they should be used in the future. They found that their results were in line with the government's estimates at the time, validating the innovative methods.
What were these methods? Check it out, it's pretty cool:
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.
They also used an imaging multibeam-sonar, which operates on the same principles as medical ultrasound. "It gives you the equivalent of black-and-white images of the cross section of the flow of oil and gas," Camilli said. This enabled the researchers to distinguish oil and gas from seawater, Camilli said.
"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." (source)
Ain't technology amazing? Now if only oil companies used the knowledge we have to actually keep their wells safe rather than cut corners to save a few bucks.
BP's robots are inspecting the well-head to see if the top kill succeeded. Image: BP
Using these thousands of sonar images, scientists got a detailed view of the oil jet's cross section, and by multiplying these average oil areas by average velocities measured, they could estimate how much oil and gas were released. These aren't just guesses based on gut feeling...
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