Chevron-contracted vessel sinks off Nigeria, 12 crew missing

(Reuters) - Twelve crew members are missing after a Chevron contracted tug boat sank on Sunday due to rough seas off the coast of Nigeria, the ship's owner said on Tuesday.

The Jascon-4 capsized early on Sunday due to "heavy ocean swells" while the vessel was "performing towing operations" at a mooring point around 30 kilometres off oil-producing Delta state, Chevron's Nigeria unit said on Sunday.

"Unfortunately all twelve crew members are still missing," a spokeswoman for the ship's owner West African Ventures said.

"Rescue operations involving sea divers are still ongoing and a full investigation into the incident is taking place," she said. West African Ventures is owned by Sea Trucks Group.

Chevron Nigeria declined to give an update.

Chevron's operates offshore and onshore joint ventures with the Nigerian National Petroleum Corp and spends around $3 billion a year on its Nigerian operations, the company says.

The U.S. energy firm's 2012 net daily production from Nigeria was 238,000 barrels of crude oil, 165 million cubic feet of natural gas and 4,000 barrels of liquefied petroleum gas.*