* Brazil well is plugged but residual oil still flows
* Chevron underestimated pressure in the reservoir
* Company estimate of oil spill expected on Monday
RIO DE JANEIRO, Nov 20 (Reuters) - U.S. oil company Chevron has taken full responsibility for a spill off Brazil’s coast, the CEO of the local subsidiary, George Buck, said on Sunday.
He said the leak from the undersea well, owned in partnership with Brazil’s state-controlled Petrobras and a Japanese group, has been plugged and the residual oil flow from undersea rock is now more than 10, but less than hundreds of barrels per day.
“Chevron takes full responsibility for this incident,” Buck told reporters in Rio de Janeiro. “We will share the lessons learned here in the hope that this sort of incident won’t happen again in Brazil or anywhere else in the world.”
Buck told a news conference that the spill was the result of an underestimate of pressure in the offshore oil reservoir that was the target of their drilling and an overestimate of the strength of undersea rock.
As a result, high pressure oil was able to leak into the well bore hole. While the well was immediately shut off, the pressure from the so-called “kick” caused the bore-hole wall to crack and oil to seep through crevices and porous rock to the seafloor and then up into the ocean.
Chevron owns 52 percent of Frade, which is producing about 79,000 barrels of oil and natural gas equivalent a day, and is the fields operator. Petrobras owns 30 percent and a Japanese Group known as Frade Japan owns 18 percent.
The well, which is being abandoned, was drilled by Transocean from their Sedco 706 rig. Buck said the problems at the well “had nothing to do with Transocean.”
The leak is about 160 kilometers (100 miles) off the coast of Brazil’s Rio de Janeiro state.
At the spill’s peak, Brazil’s oil regulator, the ANP, said about 200 to 330 barrels were leaking through cracks in the seafloor.
Buck said that estimate - which was made over the eight main days of the spill - is “in the ballpark,” adding that an official Chevron estimate should be released on Monday.