Even so, 16,000 barrels is “a pretty substantial leak,” said Edward B. Overton, an emeritus professor of environmental sciences at Louisiana State University who is studying the environmental effects of Deepwater Horizon. “But it was not enough on the surface to warrant a cleanup response.”
In this case, the oil degraded quickly, in part because of environmental forces.
The company that operates the pipeline, LLOG Exploration, believes the pipe fractured in the early morning hours of Oct. 11, a company spokesman, Rick Fowler, said in an email.
On Oct. 12, LLOG discovered that the amount of oil leaving its wells was different from the amount of oil leaving the company’s floating production system, Delta House, which is in the Gulf of Mexico, about 40 miles southeast of Venice, La.
The small crack in the pipeline has not yet been fixed, Mr. Fowler said, but the wells were shut and the flow through the pipe was stopped. What caused the fracture was unclear. The federal Bureau of Safety and Environmental Enforcement, which has regulatory oversight of the offshore energy industry, is investigating.
The authorities determined that most of the oil droplets that escaped from the pipe, which was pressurized to more than 3,000 pounds per square inch, were so small that they were measured in microns, Lieutenant Commander Youde said.
“Think of a soda can or a beer can,” he said. “If you shake it up and poke a tiny hole in it, it comes out in tiny, tiny droplets.”
Officials searched for the oil for several days before determining that it was unlikely to ever be seen, he said.
Those minuscule droplets were ingested by oil-degrading bacteria that live in the Gulf of Mexico, Dr. Overton said.
Some of the larger drops rose to the surface, where sunlight, wind and wave action helped break them down.
As a result, the spill has “some environmental impact,” Dr. Overton said, but it doesn’t appear to be measurable or significant. “You have most of the impact when the oil can congregate into a very thick layer.”
Every year, natural oil seepage — unrelated to the oil and gas industry — releases an estimated 20 million to 50 million gallons into the Gulf of Mexico, he said, from hundreds, possibly thousands of different spots on the ocean floor.
“The families of bacteria that can degrade oil already exist in the Gulf,” he said. “So when they see more oil, what happens is those bacteria degrade that oil and start reproducing.”
The bacteria eat the hydrocarbons in the oil and turn it into carbon dioxide or more bacteria, and those bacteria become a food source for other organisms.
An oil spill essentially serves as food for the bacteria, but there are times, like during Deepwater Horizon, when the bacteria are overwhelmed by the volume and cannot work fast enough to break it down.
The oil released by the LLOG fracture was originally estimated to be between 7,950 to 9,350 barrels, then revised to 16,000 barrels.
“There is a high degree of confidence in the new figure,” Mr. Fowler said.
The spill is a reminder of the importance of continuing to research the Louisiana marshlands before the next oil spill happens, Claudia Husseneder, a professor of entomology at Louisiana State University, said in a phone interview.
“That’s not if, but when,” she added. “Eventually there will be another big one that makes landfall.”