Extent of Oil Spill Remains Unclear

BY Lea Winerman  May 14, 2010 at 4:06 PM EST

Nearly a month after BP’s Deepwater Horizon oil rig exploded and sank in the Gulf of Mexico, one question remains unanswered: Exactly how much oil is spilling into the Gulf from the unchecked leak?

A 30-second video released Wednesday by BP, has provided ammunition for scientists and environmentalists who say the amount of oil spilling into the Gulf may far exceed initial estimates by BP and the National Oceanographic and Atmospheric Administration. But without more specific data, those scientists say, it’s impossible to pinpoint the number with any precision.

Since April 28, the estimate from NOAA has been that about 5,000 barrels (210,000 gallons) of oil are leaking into the ocean each day. NOAA hasn’t specified exactly how its scientists arrived at that number, though it has said that they used both satellite imagery of the oil slick on top of the water, as well as undersea video footage of the leak.

But that estimate has been criticized as too low almost from day one. Just days later, Florida State University oceanographer Ian MacDonald estimated, based on satellite images of the slick, that the oil was leaking at the rate of about 25,000 barrels (more than a million gallons) per day. NOAA administrators called that number too high, but they’ve acknowledged that their estimate is imprecise — NOAA administrator Jane Lubchenco told the Washington Post that the estimate should be seen as “5,000 barrels-ish.” Meanwhile, the video released this week — the first footage of the leak made public — gave outside scientists a bit more to work with.

But many oil exploration experts say that it is impossible to make any good estimate just from eyeballing the BP video. Bruce Bullock, the director of the Maguire Energy Institute at Southern Methodist University and a former oil company executive, explains that what comes out of an oil well is a mixture of oil, water and natural gas, and that the proportions of each can vary widely from well to well and even from the same well over time.

“The first five seconds of that clip, there’s a lot of gas coming out. And then the remainder of the clip you see more oil,” he says. “And that’s normal — you’re going to see bursts of gas. You would need to look at that over a fair period of time to determine how much liquid vs. how much gas there is. And so I think [...] any guess would not be very accurate.”

He also pointed out that it was not clear from the video how big the rupture in the pipe was — another key piece of data.

Still, the NewsHour asked several researchers whether it was possible to estimate the oil flow based on the video. Some gave it a shot, while echoing Bullock’s caution that without knowing the proportion of oil to gas and water in the pipe or the size of the rupture, any estimates would have to be very broad.

Astrophysicist Eugene Chiang, an expert in fluid mechanics at the University of California-Berkeley, said that he’d put the flow at 25,000 to 100,000 barrels per day, judging from the apparent velocity of the oil, gas and water mixture escaping from the pipe.

“If that YouTube video reflects conditions that have persisted since late April, there is little question in my mind that the amount of oil spilled has already well exceeded that of the Exxon Valdez accident,” he said in an e-mail.

UCLA professor Pirouz Kavehpour, another expert in fluid mechanics, used a different method to make his estimate — this one based on the fact that the oil jet expanded immediately after leaving the pipe. He said that suggests that the pipe is leaking about 4,600 barrels per day at a bare minimum, but emphasized that that would be the absolute minimum and the real number could be much higher.

Mirko Gamba, a post-doctoral researcher at Stanford University, used a version of a type of computer analysis called Particle Image Velocimetry (PIV) to analyze the video. In this type of analysis, researchers examine the video frame-by-frame to estimate the velocity of the escaping oil. He came up with an estimate of 30,000 to 95,000 barrels per day, assuming that the pipe was fully sheared off and that what escaped was entirely oil. That’s based on the maximum width of the pipe — 22 inches wide (the size of the pipe given by BP). That pipe is called a riser. Within it is a smaller pipe, known as the drill pipe, which helps transport the oil. To find a more accurate number, Gamba said, he would have to know from BP the actual percentage of oil vs. water as well as the size of the pipe rupture.

Some scientists are saying that BP should make this information public, and release higher-quality video for them to analyze. Timothy Crone, a research scientist at Lamont-Doherty Earth Observatory, says that with better quality video of the leak, and pictures of the rupture from a remote-operated vehicle, scientists would have what they need to make an estimate with much more precision.

If BP provided that information to the scientific community, Crone says, then “a lot of people could provide a lot of different estimates, and that would converge on the truth.” BP, however, says that it is more important to concentrate on how to stop the flow and clean up the spill than on estimating its extent more accurately.

“The estimate of 5,000, which again is provided from NOAA, is helpful in helping us deal with [the spill],” says BP spokesman Jon Pack. “But if it was a slightly different number, it just wouldn’t affect what we are doing.”