Climatide

Just how much oil did the Deepwater Horizon well spew into the Gulf of Mexico?

A study published online in today’s issue of Science Express is the first attempt by academic researchers to answer that question using scientific techniques. Two scientists from Columbia University – including one who contributed to NPR’s on-air rebuttal to BP’s 1,000 barrels a day claim back in May – now put the total at 4.4 million barrels, give or take 20% (that’s 880,000 barrels). That’s close (in the grand scheme of things) to the government’s estimate of 4.1 million barrels.

So how did they arrive at this magic number? They used a technique called optical plume velocimetry, which means they analyzed high-resolution video of the well head to estimate the rate at which oil was flowing (remember when BP said that couldn’t be done?). This particular study is based on two video clips – one before and one after the removal of the collapsed riser pipe from the blowout preventer on June 3rd. Each clip was just 20-30 seconds long. Here’s an example from after the riser had been cut:

Two 20-30 second clips. Less than a minute of video out of 86 days of gushing oil. It’s not a lot to work with, but it’s about all BP and the government have released (The publicly viewable webcam footage wasn’t high enough resolution for accurate measurements, so the US Senate Committee on Environment and Public Works made the clips available to the Columbia team).

The researchers are forthright about the weaknesses in their analysis. “We clearly acknowledge the limits of our technique; we’re unlikely to ever know the exact figure,” said lead author Timothy Crone. Coauthor Maya Tolstoy added “This is not the last word. It is the first peer-reviewed word. But we think it’s a really good ballpark.” Crone and Tolstoy point out that the flow rate could have varied day to day. Also, there were several leaks from smaller holes further up the pipe that aren’t included in the video. So 4.4 million barrels is likely an underestimate. What is clear is that the Deepwater Horizon well released almost ten times the Exxon Valdez spill, creating an horrific environmental experiment of unprecedented proportions.