Transocean, the Deepwater Horizon rig operator, is also the driller responsible for this spill—more proof that industry claims of "lessons learned" is unmitigated hogwash.
November 19, 2011
A leak at an offshore Chevron drilling site off the coast of Brazil may have dumped around 110,000 gallons of oil into the Atlantic Ocean, Brazilian officials said Friday.
Officials think between 8,400 to 13,800 gallons of oil leaked each day from Nov. 8 through Tuesday, Ibama said in a statement on its website. Chevron had said that only 16,800 to 27,300 gallons in total leaked into the ocean.
Officials are still investigating the cause of the leak, which has been almost entirely contained, but the Ibama statement said it was a result of drilling.
An official at Brazil's Federal Police, which has opened an investigation into the spill, said Chevron "drilled about 500 meters (1,640 feet) farther than they were licensed to do." The official, who agreed to discuss the matter only if not quoted by name, said that information came from a person with knowledge of the drilling.
The leak occurred at a drilling site about 230 miles (370 kilometers) northeast of Rio de Janeiro.
Rio state Environment Minister Carlos Minc said earlier he was sure the leak was larger than Chevron estimated and he called for more transparency from the company.
...
Marine life in the area of the spill will be affected by the leak, Minc said, adding that whales are migrating from north to south through the spill area.
The oil slick, which was moving away from the coast, grew to 11 miles (18 kilometers), Ibama said. Most of the oil was concentrated around the drilling rig in a layer about 3 feet (1 meter) thick.
Chevron said "current estimates place the volume of the oil sheen on the ocean surface to be less than 65 barrels."
...
The oil is believed to be coming from seep lines in the seafloor near the well and not from the well itself. Natural seeps are common around the world — perhaps the most well known in the U.S. is the La Brea Tar Pits in the heart of Los Angeles — and are often used by oil companies during undersea exploration to determine where a good prospect for oil drilling may be.
Natural seeps are usually so small in volume they don't cause a nuisance beyond producing the periodic tar ball that washes up on a beach.
But problems with drilling a well nearby can exacerbate the seeps and cause greater flow of oil, which can be hard to control, said George Hirasaki, a Rice University engineering professor who was involved in the Bay Marchand oil containment effort for Shell off Louisiana in the 1970s.
"Anytime there is movement of fluids, even if it didn't go to the surface of the well, the internal flow could result in the fluid going somewhere else," Hirasaki said. "It could move laterally at the same depth or increase the flow rate of natural seeps that are connecting to the surface."
Investigators will want to look at whether the weight of the mud being used during the drilling and abandonment operations was sufficient to contain the pressure inside the well, and they will also want to see whether drilling too deep caused problems in a geopressure zone beneath the seafloor, experts said.
Ed Overton, a Louisiana State University environmental sciences professor, said that to truly control the leak could be difficult.
"If you have this stuff oozing up through the ground you don't have a mechanism for control," Overton said. "If something started that to leak, that would worry me a lot more than a leak around the well. You'd have to drill a relief well and intercept that ooze."
...
