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The Brent oilfield operated by Shell UK Limited was once one of the most productive parts of the UK's offshore assets but is now nearing the end of its useful life. Oil production from Europe, Africa and the Middle East flowing West tends to be priced relative to oil from the Brent field, i.e. it forms a benchmark.
Shell initially named all of their UK oil fields after waterbirds in alphabetical order by discovery - Auk, Brent, Cormorant, Dunlin, Eider, Fulmar and so on. Brent refers to the Brent Goose, although it is also an acronym for the members of the Jurassic Brent formation that make up the field: Broom, Rannoch, Etive, Ness and Tarbert (in turn named after features in the Scottish Highlands).
Situated in the East Shetland Basin, the Brent is the archetype for many of the fields in the area, consisting of a tilted fault block exposing the eponymous Brent formation next to bounding faults which allowed migration from deeper adjacent "kitchen" areas where the Kimmeridge Clay Formation becomes fully mature and releases hydrocarbons. Unusually on a world-wide scale (but common in this basin), the seal or cap rock for the reservoir (which stops the hydrocarbons from migrating further towards the surface) is also the Kimmeridge Clay. The field supplies oil via the Brent System pipeline to the terminal at Sullom Voe, while gas is piped through the FLAGS pipeline ashore at St. Fergus on the north east coast of Scotland.
The Brent field is exploited by 4 platforms in an irregular SSW-NNE line. The first in place was the concrete legged "Condeep" Brent Bravo in 1975, followed by the concrete legged Brent Delta, Brent Charlie and steel-jacket Brent-A (as of 2004, the platform still produces oil through a manifold all Brent Alpha fluids are produced across to Brent Bravo). A fifth installation, the floating Brent Spar served as a storage and tanker loading buoy and was installed early in the field's construction. The "spar" design of this installation lead to the name by which it became the best known of the Brent installations (outside the oil industry). The field also included a remote flare, the "Brent Flare", which was used to flare off excess gas before gas handling and export facilities were installed in the field. This unit was decommissioned and removed using a heavy lifting barge in 2005.
The field underwent a massive £1.3 billion upgrade project in the mid 1990's which involved depressurising the entire reservoir and making extensive modifications to three of the four Brent platforms to convert them to low pressure operation which unlocked significant quantities of natural gas from the reservoir and extended the field life out to 2010+.