Scientists raise estimate of spill rate once again

By Tom Eley

16 June 2010

A team of government-sponsored scientists on Tuesday once again sharply increased its estimate of the rate oil is gushing into the Gulf of Mexico.

The Flow Rate Technical Group now estimates that the well is losing between 30,000 and 60,000 barrels of oil a day one mile beneath the ocean’s surface, a dramatic increase over the group’s previous estimate of 25,000 to 30,000 barrels.

On the high-end estimate, the BP spill is producing every four days the equivalent of the Exxon Valdez, until now the worst spill in US history.

It was not immediately clear whether or not the latest increase in the estimated rate of the spill is owing more to improvements in measuring it or to BP’s decision to cut the riser pipe in the first days of June to install a containment cap.

The previous estimate of 25,000 to 30,000 barrels was based largely on video imagery of the spill taken before the riser cut. The new estimate is based on higher-quality video imagery, plus a sonar measuring device and other methods to assess the spill rate after the cut.

If both estimates are fairly accurate—which means the cutting of the riser pipe increased the flow of oil into the Gulf—then somewhere between 57 million and 75 million gallons have been spilled so far, not including the several million gallons BP claims it has siphoned off since June 3. If the new estimate is accurate for the spill’s entire duration, then somewhere between 66 million and 112 million gallons have been spilled. The latter figure is more than ten times greater than the Exxon Valdez spill.

The new estimate is the latest in a long series of upward revisions in the spill rate, and there is no reason to believe it will be the last. Originally, BP and the Obama administration claimed that there was no oil spill. Since then the estimated spill rate has gone from 1,000 barrels a day, to 5,000 barrels, then to 12,000 to 19,000 barrels, until last week’s estimate of 25,000 to 30,000 barrels.

“As we continue to collect additional data and refine these estimates, it is important to realize that the numbers can change,” said Secretary of Energy Steven Chu. “In particular, the upper number is less certain.”

Stonewalling from BP and the Obama administration has hindered understanding of the scope of the spill. Until recent days scientists have been blocked from using the sonar device to measure the spill—though BP was aware of its availability even in early May. Likewise, scientists using particle image velocimetry have reported that BP until recently failed to provide them with high-quality video to analyze the spill.

A live feed of the spill site continued to show oil gushing out in a massive, billowing cloud.

The fragility of BP’s efforts to siphon the oil to tankers on the surface was underscored on Tuesday when a lighting strike on the Discoverer Enterprise caused a fire and suspended operations completely for five hours. Climatologists predict an especially active hurricane season, raising the prospect that siphoning could be suspended for days at a time throughout the summer.