Royal Dutch Shell is poised to announce the sale of three of its assets in the North Sea as the company speeds up its plan to divest $15bn (£9bn) of assets.

Staff at the Anglo-Dutch oil major were briefed about the sale of the Anasuria, Nelson and Sean assets during the last few days and an announcement by the company is expected shortly, The Telegraph can reveal.

The company signalled in January that it would offload maturing upstream assets in the North Sea as the new chief executive Ben van Beurden.

In a statement to The Telegraph, Glen Cayley, Vice President Upstream Shell UK and Ireland aid: “These changes are very much in line with our strategy and will allow us to focus on where we can add value to ensure a long term future for Shell in the basin.”

“We are talking to staff about the proposal to sell the assets in order to be as open as possible, whilst confirming our commitment to the North Sea.”

The sale marks the latest disposal by Shell after the company offloaded stakes in a Brazilian oil project and Australian liquefied natural gas venture since the beginning of the year. It also comes amid growing uncertainty over developments in the North Sea.

In its latest closely watched market report published on Wednesday, the Organisation of Petroleum Exporting Countries (Opec) said that projected output from the UK’s North Sea region in 2014 could fall to an average of 800,000 barrels a day (b/d) of crude, a fall of 70,000 b/d from 2013 when output hit its lowest average since 1977.

“The UK is an important business region for Shell, and our investment strategy continues to focus on assets where we see an opportunity for growth using our world-class technological know-how,” said Mr Cayley.

The assets for sale are:

• Anasuria is a Shell-operated, manned floating production, storage and offloading (FPSO) installation for the production from four subsea fields: Teal, Teal South, Guillemot A and Cook. It is located 115 miles east of Aberdeen operating in 82 metres of water, producing gas and oil. Shell has a 50pc equity share, and the joint venture partner is Esso Exploration and Production UK Ltd with a 50pc holding. Shell has a 25.77pc share in Cook. Other owners are: Ithaca Energy 41.35pc, Summit Petroleum Limited 20pc, Esso Exploration and Production UK Limited 12.89pc.

• Nelson is a Shell-operated, manned platform approximately 124 miles east north east of Aberdeen, and includes subsea tie-backs to Howe and Bardolino. Oil is exported to Sullom Voe and the gas is exported via the Fulmar pipeline to St Fergus. The co-venturers are Shell (58.1pc), Esso Exploration and Production UK (21.23pc), Apache North Sea (11.52pc), Idemitsu Petroleum UK (7.48pc), and Premier Oil ONS (1.66pc).

• Sean is a Shell-operated, manned, two bridge-linked platform, a wellhead platform, and a production platform located in the Southern North Sea 68 miles north east of Lowestoft. It produces gas which is exported to Bacton. Shell has a 25pc equity share, and the co-venture partners are Scottish and Southern Energy (50pc), and Esso Exploration and Production UK Ltd (25pc).