Elgin / Franklin

The water depth at the location of the Elgin and Franklin fields is 93m. The two fields are situated approximately five and a half kilometres apart. Both fields have similar wellhead platforms. Each is connected to the Elgin Production/Utilities/Quarters (PUQ) platform, which separates produced hydrocarbons into gas and liquid components. The Elgin wellhead platform is linked to the Elgin PUQ platform by a 90m long bridge. The bridge provides access for personnel. It also provides a route for cables and piping – it takes hydrocarbons from the wellhead platform and carries electrical power, water for fire fighting equipment and other utilities to the wellhead platform. The Franklin wellhead platform is linked to the Elgin PUQ platform by a subsea pipeline bundle. Both of these wellhead platforms are normally unmanned and are operated remotely from the Central Control Room on the Elgin PUQ platform.


Export

Hydrocarbons from the Elgin and Franklin reservoirs are separated and processed on the Elgin PUQ. Liquids are transported via the Graben Area Export Line (GAEL) pipeline and the BP-operated Forties pipeline System to Cruden Bay, north of Aberdeen. The liquids are then piped south to the BP-operated Kinneil terminal for final processing and storage prior to loading onto oil tankers for export. Gas is exported via the Shearwater Elgin Area Line (SEAL) pipeline to the Shell-operated Bacton terminal in Norfolk where it is routed either to the UK's National Grid, or via the SEAL Interconnector LinK (SILK) pipeline to the Interconnector Terminal and onwards to Europe.

An industry innovation

A number of engineering studies were completed to evaluate alternative designs for the Elgin PUQ platform. A jack-up platform design was finally selected as it offered a number of advantages. The platform could be fully fabricated with the topsides and hull assembled and tested onshore, allowing substantial savings to be made in terms of offshore commissioning. In addition, its design enables the PUQ platform to be re-floated and completely removed from location at the end of the life of the fields.


Additional safety features

The separation of the two wellhead platforms from the PUQ is an integral safety feature on the PUQ platform. High risk zones are located as far away as possible from living quarters. They are also separated by fire and blast walls. All three platforms are equipped with free-fall lifeboats, liferafts and other essential safety equipment.


A technological leader

One of Elgin/Franklin's technological challenges was to develop equipment to withstand extreme HP/HT conditions. The equipment must operate reliably at a design pressure of 860 bar and at design temperatures between -35°C and +190°C. Design and manufacture of the emergency shut-down valves (ESDVs) took almost 5 years. They are the largest HP/HT valves in the world. Another challenge was during the drilling phase – well pressure could vary between 650 bar and 1100 bar. This had to be anticipated and the correct weight of mud calculated to avoid a blow-out. To tackle this problem, we developed a new computer program which determined how to control the well pressure by varying mud density, circulation rates and pipe tripping speeds. This enabled the production wells to be drilled at much lower cost than the original exploration wells and with much less risk.