LONDON- Royal Dutch Shell and Ithaca Energy have given the go-ahead for upgrading the Pierce oilfield in the British North Sea so that it can produce natural gas, Shell said on Thursday.

The project involves modifying the existing floating production, support and offloading (FPSO) vessel and installing a sub-sea gas export line from the FPSO to the SEGAL pipeline.

It also involves drilling new wells in the field, which now produces oil and reinjects gas into the reservoir.

"This important development of the Pierce field will allow us to unlock additional gas reserves for the UK," said Steve Phimister, head of Shell's North Sea.

Pierce is Shell's eighth final investment decision in Britain's Continental Shelf since the start of 2018, Phimister added.

It is a joint venture between Shell, which holds a 92.52% stake and Ithaca Energy, which is held by Israel's Delek Group, with a 7.48% stake.

(Reporting by Ron Bousso; Editing by Edmund Blair) ((ron.bousso@thomsonreuters.com; +44 (0) 2075422161; Reuters Messaging: ron.bousso.reuters.com@reuters.net))