Conoco has become the first European user of a standardised offshore platform design that promises to make smaller, once uneconomic North Sea gas fields viable.
Last week, the company launched an adaptation of the Sea Harvester minimum facilities type platform, originally produced by US firm Atlantia for the Gulf of Mexico, for use in the 165 billion cu ft Boulton field off the Lincolnshire coast.
Design modifications were carried out by Lowestoft-based debrecht-SLP Engineering, according to a concept safety case and separate structural package presented to Lloyds Register by SLP.
SLP first looked into licensing Sea Harvester for the North Sea three years ago, according to Paul Thomson, its project manager.
`Several factors impressed us about the basic concept,’ he says. `The structural configuration is very efficient against wave loading because of the platform’s four slender columns above the waterline.’
Another important issue was the speed with which Sea Harvesters can be built. `Before Boulton, my most recent experience had been on a project in which we took two topsides and two jackets to loadout, fully completed and commissioned on-shore, in 16 months. At the time, we thought it was a world record; Boulton has been designed, built and commissioned in 10 months. There are variables, but we feel confident that we can repeat the schedule,’ says Thomson.
The platform cost 45% less than the company’s previous platform for the nearby Ganymede field, lifting Boulton from a marginal to a viable project.
The main modifications for North Sea use involved ship impact requirements, fatigue life and the base structure.
`I do not think they pay as much attention to ship impact in the Gulf of Mexico because they have boat landings designed into platforms, which we don’t. We have designed Boulton for impact from a 3,700tonne supply ship arriving at about 2m/s,’ says Thomson.
`Also, we have worked towards a 200-year fatigue life, effectively negating much of the need for inspection.
`Finally, to deal with the more rugged North Sea environment we have thickened some of the members in the substructure.’
The long lifespan will reduce maintenance and could allow the platform to be moved and reused in fields of similar water depth.
Boulton was built at Lowestoft under an engineering, procurement, installation and construction contract, which also covers hook-up, offshore commissioning and handover.
The platform will not usually be manned, but controlled via communication links to the Theddlethorpe Gas Terminal. Two wells will be sunk through the columns, with the first due to go live in October, and the second in April 1998. Conoco is partnered at Boulton by Lasmo North Sea and British-Borneo Oil & Gas.