Chevron says pressure error led to Brazil leak: report

SAO PAULO (Reuters) - A miscalculation of the pressure in Chevron's offshore Frade project led to an oil spill off Brazil's coast last week, a local newspaper said on Saturday, citing the president of Chevron Brasil.

The leak occurred because there was a mistake in the injection of heavy mud in the reservoir to prevent the return of oil through the pipe, O Estado de S.Paulo newspaper said.

"We underestimated the pressure in the reservoir. The weight of the mud was planned for another pressure," George Buck, the president of Chevron's subsidiary in Brazil, was quoted as saying by the daily newspaper.

The Frade field is located in the Campos Basin, which produces most of Brazil's oil, in water depths of 1.2 km (3,800 feet).

Chevron had said previously the leak was from a natural seep on the seabed and was unrelated to Frade's production. The company is now investigating why the pressure was miscalculated and why the leak happened, Buck said.

The newspaper also said Brazil's federal police is investigating whether Chevron was improperly trying to reach an area deep under the ocean floor known as the subsalt - a region the size of New York state that is believed to hold about 50 billion barrels of oil reserves.

The capacity of the drilling rig the company is using in the project reaches up to 7,600 meters, while the oil reserves in the area are located at about half of that distance, according to experts at ANP, the national oil agency, O Estado said.

"One of the hypotheses we're working with is that the accident could have occurred because the company drilled beyond the allowed limits," said Fabio Scliar, the head of the Federal Police's division of environment and historical patrimony, according to the newspaper.

The company is allowed to drill further distances as long as it communicates its plans to ANP in advance, the newspaper said.

Scliar had told Reuters earlier this week that early evidence showed Chevron's drilling went about 500 meters beyond what it was permitted.

The police also are investigating whether Chevron has foreign employees working illegally in the country.

Officials at Chevron in Brazil were not immediately available for comment.

Brazil is sitting atop massive deep-water oil reserves that were discovered over the past half decade. The government is keen to tap these resources as a new source of revenue for federal, state and municipal governments.

(Reporting by Inae Riveras; Editing by Paul Simao)