Teams of workers are mobilizing in the Gulf of Mexico to try to stem a natural gas leak at an offshore drilling rig that exploded and caught fire Tuesday. The rig off the Louisiana coast has been partially destroyed by the out of control blaze, and firefighting boats are on the scene.
While that might call to mind images of the BP oil disaster in 2010, experts say the incidents are vastly different.
Chris Reddy, an oil spill expert and chemist from the Woods Hole Oceanographic Institute, was among the scientists who followed the fate of the BP spill, when the Deepwater Horizon oil rig blew up and leaked millions of gallons of oil into the Gulf.
Reddy says that while deep-sea gas reservoirs may sometimes contain oil, it's highly unlikely the accident at Well A-3 adjacent to a "Hercules 265 jack-up rig" would leak anything like the BP spill.
Observers reported seeing a thin sheen on the ocean surface Tuesday. But the latest reports from the federal Bureau of Safety and Environmental Enforcement say the sheen has since dissipated -- unlike the vast stretches of sheen from the BP spill that fouled fragile marshlands along the Gulf Coast.
The lack of sheen suggests the only thing crews have to deal with is leaking gas, according to Tadeusz Patzek, a petroleum engineer at the University of Texas, Austin.
A lot of reservoirs in the Gulf of Mexico are gas-rich or gas-only, Patzek explains. Many wells produce both gas and "hydrocarbon liquids" such as ethane, propane and butane. These liquids can form a sheen on the water's surface but are quick to evaporate.
That's especially true with hot weather and windy conditions, Reddy notes. "These thin light sheens they are seeing, they can go away relatively quickly," he says.
So far, bureau officials say they haven't determined how the gas leak started or where it is. With the platform still on fire, repair crews can't yet get close enough to investigate. A spokesperson for the agency says beams supporting some of the rig have collapsed.
The jack-up rig is owned by Hercules Offshore, which is based in Houston, and the well is owned by Walter Oil & Gas. The Bureau of Safety and Environmental Enforcement reports that the well platform and rig are located 55 miles offshore in 154 feet of water. Tuesday's blowout occurred while workers were constructing a "sidetrack well" to connect with an existing well bore that extends down to the seafloor.
One way to stem the flow of natural gas is to drill a relief well -- a standard emergency measure to stop uncontrolled flows from oil and gas wells.
BP drilled relief wells during the Deepwater Horizon spill. These are drilled into the seafloor and then toward the original well, which they intercept to divert the flow into new, secure wells. With BP's Macondo well, that process took months.
Patzek says if the gas rupture is at the platform, engineers won't have to drill relief wells into the seabed to divert the flow and extinguish the rig fire. Instead, they'll just need to deprive the flames of oxygen on the platform.
"Gas is gas," Patzek says. "You need to snuff it out by whatever means possible." That would be a combination of water and foam, the same sort of firefighting technique used for oil rigs that are on fire. Once they find the source of the leak, they can plug it or divert the flow through new pipes.
If the break is on the seafloor where the well bore penetrates the earth, gas could be flowing into the ocean. But natural gas is mostly made up of methane, and in deep wells, the methane would most likely dissolve before it gets to the surface.
Once dissolved, it's eaten by bacteria. "Methane is the best thing they can eat," Patzek says.
In the Deepwater Horizon accident, lots of natural gas as well as oil escaped into the water before the Macondo well was capped. Scientists determined that methane-eating microbes degraded much of that gas without evidence of serious harm to the environment.
And, of course, natural gas is easier to deal with than oil, since it doesn't float on the surface and foul beaches or animals.
"This is no Macondo oil spill," Patzek says.
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