Gulf of Mexico oil spill: How bad is it?

The oil spill that resulted from the explosion and sinking of an oil rig in the Gulf of Mexico last week is becoming more worrying as it continues to spread and efforts at stemming the flow of the leaking oil are being met with difficulties.

The oil spill that resulted from the explosion and sinking of an oil rig in the Gulf of Mexico last week is becoming more worrying as it continues to spread and efforts at stemming the flow of the leaking oil are being met with difficulties.

 Here is what you need to know about the situation so far and how it might develop in the future.

How big is the oil slick and how fast is it growing? 

The oil slick has grown in size since the initial accident as the oil spreads across the surface of the ocean. The lighter the oil is, the faster it can spread — so gasoline would spread faster than thicker, black oils, such as the crude oil from the Deepwater Horizon. But even heavy oil can spread quickly in a major spill, spreading out as thin as a layer of paint on a wall in just a few hours, according to the U.S. National Oceanic and Atmospheric Administration (NOAA).

Officials combating the spill estimate that the oil slick has a circumference of about 600 miles (about 970 kilometers), though the shape of the spill is irregular. The slick is big enough to be seen from space.

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So far the oil slick has not spread out enough to reach the coastline, though officials are concerned about that possibility. The most recent NOAA report on the spill says that the edge of the area with visible oil is now 21 miles (34 km) from the nearest point of land, which is the SW Pass at the tip of the Mississippi River Delta.

Winds over the next few days will tend to push the oil towards the shore, though officials don't expect it to reach land in the next 72 hours.

How does this spill compare to the Exxon Valdez disaster? 

When BP's oil rig off the coast of Louisiana exploded on April 22, a ruptured pipe began emptying 136.4 tons of oil a day into the Gulf of Mexico. At that rate, the spill will have unleashed 818 tons of crude oil into the sea by the end of Wednesday, April 28. And while that that may sound like a lot, that leaves this spill only 1/50th the size of the Exxon Valdez spill. Assuming a sustained rate of leakage, it will take another 250 days for the spill to reach the size of the 1989 Alaskan catastrophe.

How is the oil leaking out? 

The initial oil slick came from the oil that was already aboard the rig that sank. Officials are not certain how much of the estimated 700,000 gallons (approximately 16,700 barrels) on the rig burned up in the fire that raged before the rig sank.

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Initially, emergency responders didn't think that any oil was leaking out of the well on the ocean floor some 5,000 feet (1,524 meters) below the ocean surface, a distance roughly equivalent to five Eiffel Towers. A valve is supposed to automatically seal off the well to prevent any leakage. Over the weekend, officials realized that the valve had not activated and that oil was indeed leaking from the circuitous set of pipes that led from the well to the rig.

"There's still flow there coming from the well head. The well head is supplying the leaking oil. It's coming up from the well head, going out into the drill pipe and into the riser. It's coming out of [a] kink or a bend in the riser," said Coast Guard Petty Officer Connie Terrell, who is currently working for the Deepwater Horizon Response Joint Information Center. The riser is a protective covering around the drill pipe that also connects the pipe to the drilling rig.

The kink or bend in the riser probably occurred when the rig went down, because it is attached to the rig, said Paul Bommer, a petrogeologist at University of Texas at Austin.

Why can't they plug the leak? 

To plug the leak, Remotely Operated Vehicles (ROVs) have been deployed to try to trigger the blowout preventer (BOP), a valve that, when activated, would secure the leak, Terrell explained. The valve is located at the well head on the ocean floor.

"Right now, what the ROVs are doing is pumping a hydraulic fluid into the blowout preventer, in hopes to build pressure [to] close the hydraulic valve," Terrell told LiveScience. "The valve is supposed to work automatically, so now we're trying to come up with different ways to activate the blowout preventer manually."

The BOP's malfunction in this case — something that Terrell said is uncommon — will be part of ongoing investigations into the incident.

The ROV robot subs, manufactured by a company called Oceaneering, have been an integral part of the effort to control the leaking oil.

"The ROVs are our eyes and our hands down there," Terrell said. "We can't just go down 5,000 feet and work in that environment. So, they are definitely playing the biggest role."

The ROVs are controlled by personnel on land. So far, their attempts to activate the shut-off valve have been unsuccessful.

"We've been trying for several days to activate it," Terrell said. "Nothing we've been doing has been successful in securing the leak so far."

Engineers around the world are working together with BP to devise other ways to activate the valve and contain the leak.

What other ways are they trying to stop the oil from leaking? 

In addition to using ROVs to try to plug the leak, BP announced on Tuesday that they plan to begin drilling a separate relief well to redirect some of the leaking oil.

According to news reports, this $100 million operation will take pressure off the blown-out well, and BP plans to begin drilling Thursday regardless of whether the response team reaches the valve at the well's head to shut off the leaking oil.

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The purpose of the relief well is two-fold, explained Terrell. The first part is to lessen the amount of oil that is leaking, while simultaneously blocking the current flow of oil by hardening and capping the well to prevent further leakage.

"The drilling rig would begin drilling down at an angle, and they would meet up with the well, and that would release some of the oil that is currently in it. The oil would go up in the relief well," Terrell said. "The other part is [that] they would put a heavy liquid in there – heavier than the oil. It would harden and make a cap in that well that would prevent the flow of oil from those two leaks, which is what the blowout valve would have done."

The relief well, which would stop the flowing oil, will take several months to complete, but is meant to be a more permanent solution to the oil leak situation.

How are they trying to clean up the oil? 

Efforts are already in place to collect some of the oil that was spilled into the Gulf of Mexico.

Skimmers, which are large vessels that attempt to remove as much oil from the water as possible, have been on the scene to clean parts of the spill.

"So far, they've been able to collect more than 260,000 gallons (984,207 liters) of the oily water mix," Terrell stated.

According to the U.S. Coast Guard, more than 29,280 feet (8,925 meters) of boom has been assigned to surround and contain the spill, and 49 response vessels are being used, including skimmers, tugs, barges and other recovery vessels.

Engineers are also working on building domes that could be placed over the leaks to cordon off the area and collect the oily water. The domes, which would reach all the way to the ocean floor, would be placed over each leak, essentially closing off the area, and inside, large tubes would funnel the oil to the water's surface for collection by clean-up crews.

The specifications of the collection domes are still being worked out, and engineers are figuring out how to employ them effectively and safely.

"Collection domes have been used in the past, but in shallower waters," Terrell said. "So, they've never been used at depths of 5,000 feet (1,524 meters)."

Why would they try to burn the oil slick? 

Burning oil spills is a known an accepted practice to clean up oil spills. "It's one of the tools in the toolbox of things you can do to help mitigate any oil spill," said Edward Overton, a professor emeritus of environmental sciences at Louisiana State University, though this method is typically used more in marshes close to shore.

If crews do attempt to burn the current slick in the Gulf of Mexico, as was announced today, it would be one the largest spills that burning has been tried on, according to Overton. "I'm not aware of something of this magnitude," he said. "Everything about this [spill] is uncommon."

To do a controlled burn, boats will first have to round up the oil with large V-shaped floating booms — the oil collects at the crux of the V. After it's collected, the oil is ignited in a remote area. The workers will try to burn the oil at the surface, where it still has plenty of its most flammable compounds and before it spreads too thin to effectively ignite. Although the oil burns quickly (a burn lasts for about an hour), workers would need to keep collecting and burning oil, probably a couple of times a day. It would likely be an ongoing process until the well on the ocean floor is capped, Overton said.

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This maneuver would be "incredibly difficult to do," Overton said. Partly this is because of the gunky components — called asphaltenes, similar to the materials used to make asphalt roads — that are still in crude oil. These gunky components don't burn as easily.

But whether or not the burning will work is still up in the air. Workers would need to get the gunk-filled oil to burn, and even if they did, they might not be able to burn the spill every day, since the sea conditions can't be too rough.

"I think it's probably a 50-50 proposition, that doesn’t mean you shouldn’t try it," Overton said.

Though the option is difficult, it still remains a viable one.

"[Oil spill] burning is complex, but it is a heck of a lot better option than letting that oil get on shore," Overton told LiveScience.

And the burn is not expected to impact any wildlife in the area.

"No populated areas are expected to be affected by the controlled burn operations and there are no anticipated impacts to marine mammals and sea turtles," according to a statement released by the joint response team to the incident.

How will the oil spill affect wildlife? 

The biggest concern over the effect the oil spill could have on wildlife would be its effect on coastal wildlife. So far the oil has not reached the coast and officials are putting up barriers as a precaution. The earliest it would show up on shore would be this weekend, ecologist Bill Starkel with the U.S. Fish and Wildlife Service told LiveScience.

Officials from NOAA are currently evaluating the effects the oil could have on sensitive habitats and shorelines in four states: Louisiana, Mississippi, Alabama and Florida.

"The challenge with this type of oil is it's going to float, and depending on what the wind and waves do it may stick around for a while either mixing out there at sea or ultimately it could show up on shore somewhere and that poses other issues," said Tom Brosnan of NOAA's Assessment and Restoration Division. "As you get closer to the shorelines you tend to find richer life."

Along coasts, birds are a big concern. When coated in oil, birds' feathers lose their ability to trap air and repel water. The result: Birds can't hold in heat and they become hypothermic, according to the Oiled Wildlife Care Network. To keep warm, an oil-coated bird will increase its metabolism, which takes energy and so means a greater need for food. Unfortunately, at the same time the sticky feathers can disrupt the bird's buoyancy so it doesn't float as well. The sinking makes it tricky for the bird to snag much-needed food.

But coastal species aren't the only wildlife potentially threatened by the spill. Here are some of the animals that might come into contact with the oil slick as it moves out in the open ocean, Brosnan said:

 • Fish: open-water species, such as tuna, sailfish and Jacks
 • Birds: pelagic birds, such as shearwaters and frigate birds
 • Mammals: fin whales, sperm whales and bottlenose dolphins
 • Turtles: loggerheads and Kemp's ridleys

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 Additional reporting by Denise Chow, Jeanna Bryner, Rachael Rettner and Stuart Fox. 

IN PICTURES: Destructive Oil Spills