Getting the job done: beating corrosion to deliver a North Sea oil platform

Ben Hogben, process engineer, CB&I UK Ltd, MEng chemical engineering, University College London (2000)

The project in brief

• PROJECT The Buzzard development consists of three bridge-linked steel platforms that support facilities for drilling and production, and utilities and accommodation. It will be located offshore in 100 metres of water, 100 kilometres north east of Aberdeen and 55 kilometres off the coast at Peterhead.
• CLIENT Nexen Incorporated, which entered the UK North Sea in 2004 with US $2.1 million acquisitions.
• REASON FOR PROJECT Recovery of total reserves estimated to be more than 400 million barrels of oil.
• SCHEDULE Project started, September 2002; initial conceptual design and concept definition project specification (CDPS) phase, six months; detailed design, two years; construction, three years; onshore commissioning, one and a half years; offshore commissioning and start up, six months.
• COST US $2.1 billion.

The Buzzard oil field is the largest oil field to be discovered in the North Sea in the past decade. Nexen operates the field with a 43 per cent interest and the other co-venturers are PetroCanada, 30 per cent; BG Group, 22 per cent and Edinburgh Oil and Gas plc, 5 per cent. The project to design, construct and commission the three platforms and associated facilities began in September 2002 with an ambitious schedule to produce first oil just four years later in 2006.

Once operational, the field is expected to reach a plateau of 180,000 to 190,000 barrels of oil per day. Crude oil will be transported to the mainland via a pipeline tie in to the Forties pipeline system and the natural gas will flow straight to market via the Frigg pipeline system.

From FEED to full scale

I joined the project as a junior process engineer just two weeks after the contract was awarded. As well as the design, CB&I UK Ltd was responsible for the construction of the three decks, jackets and bridges, which took place at four locations: Methil, Scotland for the wellhead deck; Heerema, Hartlepool for the quarters and utilities deck; Dragados, Cadiz, Spain for the production deck; and Aker Verdal, Norway for the jackets and bridges.

During the conceptual phase I worked on simulations of the various design options available before the three-deck solution with export to the Forties and Frigg pipelines was selected. For the next phase, I moved to the utilities group to broaden my horizons. Here, we looked at large water systems such as heating and cooling medium, seawater lift and water injection. I was a member of the ‘water board’ throughout the detailed design phase and the commissioning phase. As the project progressed I became part of the start-up team and was the process engineer at the quarters and utility (QU) platform fabrication site in Hartlepool. I’ll be heading north soon to go offshore as part of the start-up and commissioning group.

The technical challenges of corrosive combinations

A particular technical challenge I worked on was the design of the water injection system used to maintain the reservoir pressure. Reservoir engineers have predicted that very little ‘produced’ water would exist in the first few years of operation, so using seawater will be the only way to maintain reservoir pressure. As we all know, untreated seawater and air are a corrosive combination and sulphates in seawater can react with barium to form insoluble residues – neither is good for pipework. The seawater required both deaeration and desulphuration. Buzzard’s sulphate removal package is the first ever to be built for an offshore installation.

The wellhead platform is already in place and Buzzard is in its hook-up phase with two of the three platforms en route to the site. Once hook up is completed, offshore commissioning and start up will begin. By the time you read this the project will be delivering oil.