Deep water oil reserves are part of a fundamental growth area for Royal Dutch Shell, the company said after starting a Gulf of Mexico project.

Shell last month said the start of oil production from the deepwater Bonga North West development off the coast of Nigeria was an "excellent addition" to a growing portfolio of offshore assets. At its peak, an offshore floating processing facility is expected to process as much as 40,000 barrels of oil equivalent per day.

The company said Monday production started at its Cardamom project, its second deepwater project in the U.S. Gulf of Mexico brought online this year.

Marvin Odum, upstream director for North American operations, said Cardamom is a high-value addition to its deepwater portfolio.

"Our future opportunities in deep water mean that this will remain an important, high-return growth area for Shell," he said in a statement.

Cardamom is about 225 miles off the coast of New Orleans in 2,700 feet of water. The oil there lies beneath a thick submarine layer of salt in rock more than four miles beneath the sea floor.