Oil giant BP and its co-venturers have approved a £3bn investment programme to upgrade and replace the existing subsea facilities at the Schiehallion and Loyal oil fields by the Shetland Islands.The Quad 204 project involves replacing the existing Schiehallion floating, production, storage and offloading (FPSO) vessel with a new FPSO, which is scheduled to be installed in 2015. The FPSO is a floating unit used to process hydrocarbons and store oil until the oil can be offloaded onto a tanker and transported through a pipeline.BP said the new vessel will export up to 130,000 barrels a day of oil and store in excess of 1m barrels. The new facilities are scheduled to commence production in 2016.Schiehallion and Loyal have produced nearly 400m barrels of oil since 1998 and an estimated 450m barrels of resource is still available, BP said in its statement. BP and Shell will each have a 36.3% ownership interest in the new FPSO vessel; Hess holds 12.90%, while Statoil (UK), OMV (UK) and Murphy Petroleum will each hold 4.84% interest.Shares of BP rose 0.6% to 455.9p in morning trading in London.AR