The Brae field, discovered in 1975, is located In block 16/7 about 42 nautical miles north west of the Occidental Piper field and 70 nautical miles of the BP Forties field The Brae ‘A’ platform was installed in 1982. First oil was exported in July 1983 and production rates of around 100,000 barrels per day have been achieved/The Brae ‘B’ platform was installed in 1987 and first oil was achieved in April 1988 The Brae ‘A’ and Brae ‘B’ platforms are connected to each other by a twin 18″ pipeline system from the Brae ‘B’ platform, oil is transported to Brae ‘A’ where it is combined with the processed Brae ‘A’ oil The combined oil is then transported via the 30″ submarine pipeline to BP's Forties Charlie platform where it enters into BP's 32″ submarine pipeline for transportation to the processing facility at Kinneil

The Central Brae project is Marathon's first sub-sea development and has been managed by a dedicated team of engineers and support staff drawn from their respective discipline departments A major part of the project are the 6″ production, 4″ service, and 10″ water injection pipelines, the retrofit caisson riser and the chemical and control umbilicals Together these represent over a third of the total development cost The development plan for Central Brae was approved by the Brae group participants in October 1987, and Department of Energy approval was received in April 1988 This paper presents a general description of the project together with a more detailed account of the design, fabrication and installation of the retrofit caisson bundled riser system

Extent of Project

The Central Brae reservoir, discovered in 1976, lies between the Brae ‘A’ and ‘B’ platforms, and is divided Into two regions The proven area, defined by four successful wells drilled to date, and a ‘possible’ area, characterised by heavy faulting and one suspect well The proven region is estimated to contain 162 mmstb of oil in place whilst the ‘possible’ area has estimated oil in place of 111 mmstb. The estimated recovery from the proven area using two producers and two water injectors to supplement some natural water influx is 64 mmstb of oil The estimated peak production rate IS 20,000 bbls/d

The artist view below illustrates the main elements of the project(Artiest View is available in full paper) A template was tied back to the Brae ‘A’ platform with 2 x 6″ production, 4″ service, and 10″ water injection pipelines. There are also two umbilicals, one for chemical injection and the other for controls New risers were required on the Brae ‘A’ platform for the pipelines and an existing J-tube was used for the umbilicals All the pipelines were trenched, except where they cross over the existing Brae ‘A’ to ‘B’18″ pipelines The production pipelines are also covered with lm of rock to prevent upheaval buckling To avoid hydrate formation and the cooling effect that the cold Central Brae oil would have on the Brae ‘A’ processing facility, thermal insulation of the production pipelines was required.

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