Statoil said on Wednesday it will delay the start up of the $7 billion Mariner field in the North Sea — the biggest field development in the UK Continental Shelf for more than a decade — by about a year.

Costs for the project have risen more than 10%.

“Statoil and its partners have decided to accept a delayed timetable for the commencement of production from the Aasta Hansteen and Mariner fields from 2017 to the second half of 2018,” said Eldar Sætre, chief executive of Statoil.

“For Mariner, the cost increase is slightly above 10% as compared to the original plan.”

The Mariner field is located on the East Shetland Platform of the UK North Sea, about 93 miles east of the Shetland Isles.

Mariner is expected to produce more than 250 million barrels of heavy oil over 30 years, with average “plateau production” of around 55,000 barrels a day.

Statoil said it is the operator of Mariner with 65.11% equity in the project and that other partners include JX Nippon Exploration and Production (U.K.) with 28.89% and Dyas Mariner Ltd with 6%.