Shutting down safely

Yokogawa UK has supplied an emergency shutdown system for a new type of offshore platform developed by Shell for the Brigantine gas field in the Southern North Sea.

Yokogawa UK has supplied an emergency shutdown (ESD) system for a new type of offshore platform developed by Shell for the Brigantine gas field in the Southern North Sea. The ESD system has been to provide basic personnel and asset protection.

The Gas Supply Group of Shell UK Exploration and Production is developing the Brigantine gas field using a novel platform concept known as Trident. The design, which was developed at Shell’s Lowestoft offices, represents a major step forward in the realisation of small gas accumulations previously considered uneconomic using conventional techniques.

The Brigantine accumulations are situated about 5km north east of the Indefatigable field, and make up the Brigantine development. The project will consist of several wells drilled from two minimum-facilities marine access Trident-type platforms, both in approximately 29m of water. The more southerly platform will be known as Brigantine BG. The second platform will be known as Brigantine BR.

Brigantine field gas will be exported via a 20in carbon steel pipeline, approximately 20km long, from Brigantine BG to the Corvette platform for onward transportation to the Leman A platform and thence Bacton onshore terminal for processing. A similarly sized interfield pipeline approximately 5 km in length will transport Brigantine BR gas to Brigantine BG. The pipelines will be rated to full closed-in tubing head pressure (CITHP).

A cocktail of hydrate suppressant and corrosion inhibitor will be pumped to each wellhead platform from Corvette via a 4in ‘piggyback’ pipeline. Electric power and controls will be provided from Corvette platform via subsea cables.

Tie-in modifications will be required at both the Corvette and Leman AP platforms to enable gas export under natural depletion from the Brigantine field. The Bacton terminal condensate stabilisation system will also be upgraded to process Brigantine C condensate, which has a relatively high proportion of LPG components.

In concept the Trident platforms are too small to allow an area to be designated ‘safe’, and consequently the ESD systems are located inside certified explosion-proof (Ex-d) boxes also supplied by Yokogawa. Yokogawa’s ProSafe-SLS logic has very high integrity and proven reliability, and will require minimum maintenance in an offshore environment. Attendance on Trident platforms is planned once per annum, and all equipment has been selected based on proven performance.

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