RIO DE JANEIRO - Hess Corp did not file a discovery notice with Brazil's government after drilling a well in the offshore Santos Basin, a company official said on Wednesday, a sign Brazil's offshore oil fields still face major risks.

Companies exploring in Brazilian fields are required to notify the government when they find signs of oil.

A Hess statement released on Monday did not say whether the company found oil in the Guarani well drilled in the BM-S-22 bloc. An official at Brazil's National Petroleum Agency was unable to immediately comment on the issue.

Brazil is advancing the development of billions of barrels of oil from fields buried under a layer of salt miles below the ocean surface in hopes of becoming a major global energy exporter.

But experts caution the operations will be exceedingly complex due to challenges of deep-sea production that is untested at a commercial level.

Exxon Mobil, a partner in the project and operator of the block, did not immediately respond to requests for comment. Petrobras is also a partner in the project.

Hess said in the statement its share of the well cost will be expensed in the second quarter.

(Reporting by Brian Ellsworth; editing by Stuart Grudgings and Lisa Shumaker)