The worst Nigeria offshore oil spill in more than a decade has been contained before reaching the West African nation's coast, officials with Royal Dutch Shell said Monday, less than a week after one of its lines leaked crude into the Atlantic Ocean.
An investigation into how the spill of less than 40,000 barrels -- or 1.68 million gallons -- happened is ongoing, though company officials acknowledged workers discovered the leak only after seeing a sheen of crude in water surrounding its Bonga offshore oil field.
Meanwhile, Shell officials said the company will clean up another spill it discovered while containing its own.
"We can undeniably say we traced our oil ... and stopped it," said Cliff Pain, who manages the Bonga operation for a Shell subsidiary.
Shell organized a helicopter flight Monday for journalists to see the Bonga field -- controlled from a large ship as opposed to a stationary rig -- about 75 miles off Nigeria's coast. There, waters appeared free of the oil sheen as ships continued to patrol along the underwater lines linking the vessel to the oil fields and the transfer buoys for filling tankers.
The leak discovered last Tuesday came from a break in a flexible line more than 360 yards from the vessel that sends oil to tankers, Pain said. While the vessel has a variety of gauges to check pressure on the line, it wasn't until daylight broke that workers noticed a sheen surrounding the Bonga vessel, he said.
It takes about 25 hours to fill a waiting tanker with 1 million barrels of oil from the vessel, Pain said. That means the leak could have spewed for hours before being noticed.
At its height, Shell statistics show the sheen spread across about 350 square miles, matching an estimate earlier issued by an independent watchdog group called SkyTruth. Nigerian government officials previously said the spill only affected an area a third that size.
Using ships and aircraft, workers spread chemical dispersants to break up the oil, which also evaporated in the region's warm water and air, said Steve Keedwell, a Shell employee who helped oversee the cleanup operation. Shell eventually stopped the sheen about 11 miles before it made landfall, Pain said.