Engineers lift hopes of raising most of the North Sea rigs

As six contractors shortlisted last week plot the disposal of the Brent Spar

Between now and April six groups of contractors will develop in detail 11 proposals for onshore disposal of Shell’s floating oil storage buoy, Brent Spar. Shell insists the original plan of deep sea dumping remains unless one of the others can be shown to be better.

Although Brent Spar has some characteristics that make it unique, all sides believe its ultimate fate will set a precedent for other North Sea structures. But the engineering community is becoming markedly more positive than the oil companies about the prospects for removing rather than dumping platforms. It estimates just seven or fewer could be difficult to remove compared to 40-50 hitherto quoted.

There is broad agreement on what to do with most structures. There are around 130 steel platforms in shallow water, weighing 2,000-5,000 tonnes. These can be removed in a single lift, and indeed it had always been planned to remove them, says Dr Bryan Taylor, technical affairs director of United Kingdom Offshore Operators Association (Ukooa).

Then there are concrete platforms in deep water, where by general agreement removal is not feasible. Greenpeace accepts there is no scope for recycling hundreds of thousands of tonnes of concrete in each, and would accept the steel topsides and any other steel being removed for recycling, and the stability tanks, which many have at the base, cleaned.

The controversy, and where Brent Spar will be seen as a precedent, concerns the 50 platforms in water more than 75m deep, of which 40 are steel. Current International Maritime Organisation guidelines call for topsides to be removed and the platform jacket to be toppled – the legs blown up in situ – to leave 55m of clear water above. Ukooa favours a case by case best possible environmental option study on each. In many cases, it believes, even if the remains could be salvaged, there would be no clear benefit.

But a European Commission study by a team led by John Brown E&C, thought otherwise. `It is well within the industry’s technical capa bility to safely remove all but a few [steel platforms] in their entirety,’ it said last November. Only seven would be difficult to remove. More recently, engineers have said the report over-estimated the difficulties associated with these seven platforms.

Later this year, a three-yearly ministerial meeting of the Oslo and Paris Commission, which regulates the marine environment in the North East Atlantic, may reconsider the IMO guidelines.

It is thought the Commission is waiting to see what emerges before acting on its report.

{{Shortlisted groups

Contractors Country Method of raising After raising from water

Brown & Root UK Raise and rotate Scrap onshoreEnergy Series with compressed gasKvaerner Stolt Norway/ Raise and rotate Scrap onshoreSeaway Alliance Nether- with compressed Use topsides as training(KSSA) lands gas. Raise centre. Use hull as dock vertically with gate. Use hull sections compressed gas as fish farm. Use hull as quay extension, NorwayMcAlpine Doris UK/ Raise and rotate Use hull as quayjoint venture France with compressed extension for Able UK gas yard TeesideThyssen Germany/ Raise vertically Scrap onshoreStahlunion/Aker Norway with jacked cable liftWood-GMC UK/ Raise vertically Use topsides as training Norway with jacked cable centre. Use hill as lift quay extension, NorwayAmec Process UK Use hull sections as& Energy coastal protection off Norfolk coast}}