Five Unanswered Questions About the Gulf Spill

Gerald Herbert / AP (left); Chris Graythen / Getty Images

The Deepwater Horizon rig in April (left) immediately after the explosion that caused the spill, and July (right) once the well was capped.

Over 100 days since the Deepwater Horizon met its fiery demise, setting off what has become the largest oil spill in U.S. history, things are finally looking up. The well has been sealed with a cap for more than two weeks. Final preparations are being made for a static kill of the well, which will fill the bore from the top with mud and cement and will be followed by a "bottom kill" of the well with mud and cement pumped in through the relief well. Even the globs of oil on the gulf's surface are beginning to dissipate. Yet there is still much to be done and a number of questions that remain to be answered.


For over a month, scientists had been estimating that the well was spilling 35,000 to 60,000 barrels of oil per day, meaning that between 3 million and 5 million barrels of oil would have been released over the course of the spill, up to when the well was finally capped on July 15.

Late Monday, federal scientists announced what they called the most precise estimate yet of the spill: nearly 5 million barrels. The figure confirms that the BP spill is the largest release of oil into marine waters. As more data on the well becomes available, the government's team of scientists will continue to refine this estimate.

More than two weeks since the oil flow was cut off, it's clear that less and less oil is visible on the surface of the gulf.

So if it's not on the surface, where is it? A large but unknown portion of it remains hidden in the depths of the gulf, either having never surfaced or surfaced and then sunk. Some has been chemically dispersed, some has been burned, and some has been weathered, eaten by oil-chomping bacteria, or otherwise naturally degraded. Some has evaporated, and some has washed ashore.

In an effort to find out, scientists are working on what's called an "oil budget," an approximation of how much oil has gone where. By taking into account the total amount of oil discharged into the environment and estimates of how much oil has come to the surface, been skimmed or burned, naturally degraded, evaporated, and so on, the scientists can deduce the fate of the oil that remains unaccounted for--such as how much still lurks in the gulf's murky depths.

Obviously this is an inexact science, based heavily on estimates, but it's a major step toward answering a complex question, and will be updated and refined as more data becomes available. Admiral Allen told reporters that the first version of this budget should be forthcoming in the next week.

The results of the well integrity test, which began as the well was sealed off on July 15, suggest that the well bore is secure and that oil has not breached it. Yet the results are not as unambiguous as engineers hoped: the pressure in the well has been rising steadily, but has not gotten as high as it was expected to. The pressure in the well is still short of 8,000psi, the point at which the test would have been unequivocally declared a success. Scientists working with BP and the government attribute the lower pressure to depletion of the reservoir--essentially that the reservoir tapped by the well had spewed out a greater percentage of its oil during the course of the spill than previously thought. "There are no indications of anomalies that would lead us to believe we have a problem with well integrity," said Allen at a news conference.

However, the admiral says that the results of the static kill, a process scheduled to begin Tuesday, in which mud and then cement will be pumped into the well from the top, should provide a clear indication of the well's integrity. If there is a precipitous drop in pressure once the mud is pumped in, that would be evidence of integrity in the well bore. On the other hand, if there is still back-pressure after the mud is pumped, that would be a bad sign and would indicate a problem with the well. "When we start the static kill, we'll know a lot more about the condition of the well," Allen said. Regardless of the results, the relief well will be completed shortly thereafter and should be able to permanently entomb the entire well in mud and cement.

The containment cap has stopped the flow of oil into the gulf. Here, the cap is lowered onto the Deepwater Horizon wellhead in mid-July. (AP)

We know at least one exists, but there are probably more. A few days after the Deepwater Horizon well was sealed off, a hydrocarbon leak was discovered about two miles away, prompting concerns that a breach in the well bore was allowing oil and gas to percolate into the surrounding rock and up to the surface. The government later attributed this leak to another well, easing the worries.

But it still seems problematic for an old well to be leaking. As the AP reported in early July, there are 27,000 abandoned wells in the Gulf of Mexico, some more than 60 years old, and all unmonitored. Theoretically, some of them could be quietly leaking, and the 3,500 that are listed as "temporarily abandoned" and therefore less scrupulously capped, are at higher risk of problems.

Any major leaks would surely be noticed, and small leaks probably wouldn't add much to the total hydrocarbon load of the gulf, which is already studded with oil and gas seeps that collectively release more than 1,300 barrels of oil each day. Yet the discovery of this new leak should probably be cause for concern about the state of abandoned wells in the gulf.

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The Gulf spill's disastrous effects on marine life (Jesse Cancelmo)

And how much damage is the spill actually wreaking ecologically? Despite the magnitude of the spill, which is by far the largest in U.S. history, its impact on wildlife appears to be smaller than experts would have expected. So far, 3,271 birds, 503 sea turtles, and 64 marine mammals (like dolphins) have been found dead, according to statistics from the Unified Command. Not even all of these were visibly oiled, though, so it remains possible that some of the deaths were unrelated to the spill.

In contrast, the 1989 Exxon Valdez spill of about 260,000 barrels into Alaska's Prince William Sound--a fraction of the amount released by BP's runaway well--killed a whopping 250,000 seabirds, in addition to thousands of sea otters and hundreds of seals.

Nevertheless, there are probably many more animals affected by the current spill than are being found and counted by response workers. "I think we're only seeing the tip of the iceberg," says Michael Ziccardi, a veterinarian who has been working with injured animals in the gulf since late April. "The question is how much of the iceberg is actually submerged. We don't know whether we're finding one in five animals that are affected or one in 50."

Scientists working as part of the Natural Resource Damage Assessment process, which seeks to evaluate the damage done by the spill and determine what the responsible parties must do to restore it, are collecting data that will eventually help them estimate the total ecological toll. Although a clear and complete picture of the spill's ecological impacts won't be fully developed for a while, the impact will surely last for a very long time.