THESE days the sight of an empty drinks can being tossed from a ferry is
likely to be greeted with tuts of disapproval. How much louder then was the roar
of protest in June 1995, when Shell towed the Brent Spar round the north coast
of Scotland ready to drop it off the edge of Europe鈥檚 continental shelf. Dumping
the 14 500-tonne North Sea oil platform would have been equivalent to throwing
341 million drinks cans into the sea鈥攕ix for every man, woman and child in
Britain. Shell soon faced fire bombs and a consumer boycott of its service
stations in Germany. At the last moment the company recanted, towed the Spar to
the shelter of Erfjord in Norway, and asked the world for ideas about what to do
with it.
Shallow grave
Today, the floating hulk remains in Erfjord and Shell is still trying to
decide its fate. Of some 400 proposals submitted, Shell has asked for 30 ideas
from 19 contractors to be fleshed out. It plans to publish a shortlist early
next year and to make a final choice by mid-1997. Meanwhile, the company retains
its licence for deepwater disposal, having previously persuaded the British
government that this was the 鈥渂est practical environmental option鈥�. And Shell
says this remains the reference point against which other ideas must be
judged.
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Only one company among the 19 has dared to suggest dumping the platform at
sea. Jan De Nul, from Belgium, proposes dredging a shallow grave 32 metres deep
on the sea bed in 100 metres of water. As the only proposal to receive outright
rejection from Greenpeace, the environmental group that spearheaded the campaign
against scuttling the Spar, it is unlikely to succeed. Of the other proposals,
some suggest reusing the main part of the vessel, while most opt for some
combination of dismantling and recycling鈥攁 job easier said than done.
One reason why dismantling will be difficult stems from the Spar鈥檚 troubled
history since construction ended in 1976. Shell built the Spar as a giant
floating oil store for the Brent oilfield, northeast of the Shetland Isles. It
was connected to production platforms by pipelines, and used as a filling point
by tankers. For a while in the late 1970s it was the only exit point for oil
from the field. But even before the Brent Spar began to operate, it had been
damaged. The 137-metre-high structure had been towed to sea in a horizontal
position and then upended. But the process of bringing it to a vertical position
subjected two of its six giant oil tanks to dangerously high stresses. Though
not noticed at the time, the upending manoeuvre is thought to have weakened the
walls of the tanks, causing them to rupture during another accidental build-up
of pressure in January 1977.
Thankfully, no major release of oil took place when the walls gave way.
Engineers repaired the damage to protect the entire structure, but the holed
tanks were never used again. A few months later, following completion of a
pipeline from the Brent oil field to Sullom Voe terminal on Shetland in 1978,
Shell relegated the crippled Spar to a back-up role before mothballing it in
1991. The weaknesses left by the accidents helped to persuade the company two
years ago that the structure was too dangerous to bring back to land, and should
be scuttled in deep water.
When the platform is at sea, the only fully visible parts are its
topside鈥攃omprising a helideck, crane and accommodation for 28 people.
Beneath the water are 12 buoyancy tanks that keep it afloat and the six storage
tanks. Below these is ballast made up of 6800 tonnes of hematite mixed with
concrete, to keep the vessel stable and vertical in the water.
Despite its huge size and mass, the Spar is extremely fragile. The internal
walls of the tanks are not designed to withstand high pressures. When in use,
engineers minimised the pressure differences across the walls by keeping the
tanks full with either water or oil. But if the tanks are emptied, the pressure
differences created within the structure might cause the walls to buckle.
According to Eric Faulds, Shell鈥檚 decommissioning manager: 鈥淩emoving the Spar
from the water or even just raising it higher, without posing undue risk to
people or the environment, requires an exceptional feat of civil engineering.鈥�
Unfortunately, if the Spar is to be dismantled, it must be progressively lifted
out of the water or turned on its side and put on a barge for towing to port.
Either exercise, says Faulds, 鈥減oses a significant risk to its structural
颈苍迟别驳谤颈迟测鈥�.
Risk of collapse
The extent of the problem with the tank walls emerged from a structural
survey commissioned last autumn from the engineering consultants WS Atkins. The
firm constructed a statistical model of the Spar with the large steel tank walls
represented by thousands of small interconnected 鈥減lates鈥�, so that the stress on
each plate could be assessed. This, say the engineers, is very conservative
because it makes no allowance for the extra strength that the entire structure
may hold. Yet, according to Shell, the analysis revealed that 鈥渁t an early stage
of pumping out, the inner walls separating the tanks from each other would reach
the safety limit and may begin to collapse鈥�. Water would pour back in and the
Spar would sink back to its original level.
Moreover, because of the two damaged tanks, pumping can be carried out in
only four tanks鈥攁nd only three if the Spar is to be raised evenly in the
water. Even if divers were sent down to repair the tanks, a dangerous operation
in itself, 鈥渢here would still be serious stress, this time on the outer walls
separating the tanks from the sea,鈥� says Atkins.
The safest solution, Shell believes, is to raise the structure physically
with giant cranes or airbags, so as to minimise the amount of pumping needed.
Atkins reckons that an 鈥渁ssisted buoyancy鈥� capable of lifting 6000 tonnes would
raise the Spar by 16 metres. Several companies propose such options as part of
their salvage plans.
Another way to lighten the load would be to remove the 1200-tonne topside. In
this case, the Spar would first have to be weighted down, bringing the topside
closer to the water so that cranes could lift it off. But this approach creates
its own problems. According to Atkins, lowering the Spar by more than about 2
metres could itself cause pressure changes in the tanks that would threaten the
integrity of the structure.
One other choice facing bidders for the disposal contract is where the job
should begin. Should the platform be dismantled in the Norwegian fjord or first
towed to port, either vertically or horizontally? According to Shell, the only
sheltered site in Britain to which the structure could be towed in a vertical
position is Loch Kishorn on the west coast of Scotland. Even then, however, the
Spar鈥檚 tanks would have to be pumped out to reduce its draught from 109 metres
to the loch鈥檚 limit of 80 metres. According to Rudall Blanchard Associates,
which carried out an environmental impact assessment on the Spar in 1994,
raising the Spar by such an amount poses 鈥渃ritical鈥� problems in maintaining
stability and ballast control.
So what solutions to all these problems have the competing companies dreamt
up? The Dutch firm HSM wants to grapple with the Spar while it is still vertical
and sitting in its fjord. It would slice the Spar crosswise into nine cylinders,
using remote-controlled cutters. The cylinders would be offered to Shell as oil
tanks for one of its refineries. The British John Wood Group would also cut the
Spar into cylindrical slices while it was still afloat. It would place the
cylinders side by side on the seabed in the Norwegian port of Mekjarvik, as the
foundations for a planned new quay.
Most firms, however, say vertical dismantling would be too dangerous for the
workforce and would increase the risk of sinking the platform. They would upend
it before towing it, probably on a barge or submersible cargo vessel, to a dock.
This is despite the conclusion of Rudall Blanchard Associates that horizontal
dismantling has 鈥渉igh potential for unplanned events, such as accidental
flooding of tanks during upending or horizontal towing, resulting in aborting
the operation or sinking of the structure鈥�.
Some companies propose using floating cranes to upend the Spar. ROS Holland
says it can do the job more safely without cranes, by juggling the volume of air
inside the tanks. 鈥淭he core of the plan,鈥� it says, 鈥渋s to decrease the stability
to a point where small heeling moments will suffice to gradually increase the
angle of inclination of the Spar.鈥� The company says the pressures involved in
the process 鈥渨ill not exceed the strength of the structural members鈥�.
Offshore casino
Once ashore, the Spar can be cut up for recycling. It contains 6700 tonnes of
high-grade steel, 28 tonnes of aluminium, 15 tonnes of zinc and 15 tonnes of
copper. The hematite ballast could be used for hard core in building or as rock
armour in sea defences. Greenpeace鈥檚 case against scuttling is partly that such
material should not be dumped on the ocean floor, and partly that it has
positive uses on land. Recycling the Spar would avoid creating 26 000 tonnes of
mining wastes, says Greenpeace. It also argues that it takes only a quarter of
the energy to recycle steel as to manufacture the same amount from iron ore.
But turning something like the Spar into tiny chunks for recycling lacks
romance. Shell specifically asked prospective contractors to produce ideas that
would capture the imagination: 鈥渁 unique solution for a unique structure鈥�. Some
novel ideas have fallen by the wayside. These include Shell鈥檚 suggestion that
the structure could be dumped in shallow water off the Norwegian coast to make
an artificial reef for fish, and a plan to create an offshore casino.
Of the remaining ideas, several companies propose turning just the topside
into a dockside training centre, though for what is unclear. Using the rest of
the structure presents bigger problems, however. A consortium headed by the
German firm Thyssen suggests installing a wind-powered generator and
desalination plant on the top and towing the entire structure to a remote corner
of Norway that lacks a local water supply.
But the most dramatic proposal for reuse comes from a Rotterdam-based
consortium of Royal Volker Stevin and Hollandia, which proposes a floating power
station. It would lift the topside off the Spar and refit it with three
windmills, then it would tow the rest of the structure to the west coast of
Scotland and reunite the two halves. Finally, it would add wave power units and
hook up the structure to the shore by a power line to supply electricity to
local communities or the national grid. Royal Volker Stevin believes its idea
鈥渕ay provide the ideal solution for other offshore structures鈥�. It suggests a
future fleet of refurbished oil platforms providing power for numerous Scottish
islands.
Grand though the plan sounds, the Spar would generate only 19 megawatts of
power. This is less than one-tenth the capacity of most modern power stations.
But unlike some other projects, it does address a genuine need for new sources
of locally generated energy. According to Birgitta Godhavn Smith of the European
Islands Energy and Environment Network based at Stornoway on Lewis in the Outer
Hebrides: 鈥淭here are hundreds of miles of coastline, heavy swell and strong
tides, and of course the Scottish islands experience more than their fair share
of wind.鈥�
But there is a growing industry consensus that the leading contender for
disposing of the Spar is the British-based company AMEC Process and Energy,
which is already planning to build a giant scrapyard on Teesside. 鈥淭he idea is
to use it to decommission large numbers of offshore installations as they finish
their lives in the North Sea,鈥� says Jeremy McTeague of AMEC, 鈥渟tarting with the
Brent Spar.鈥�
The company offers a range of possible final uses for the Spar. It could be
cut into large chunks and dumped off the east coast of England to prevent wave
erosion of vulnerable beaches. Or the chunks could form the foundations for a
causeway and marina somewhere 鈥渋n the north west of England鈥�.
But the proposed site of the scrapyard鈥攔ight next to a British Steel
plant equipped to smelt steel鈥攕uggests that the Spar鈥檚 most likely fate is
to be melted down. 鈥淭he structures could be brought in directly from the sea to
the port, cut up using hydraulic shears and thrown into the next-door furnace,鈥�
says McTeague. This solution would be the most energy efficient, AMEC claims,
and would not require any road transport to move the broken-up Spar across the
country. In addition, the tonnes of barnacles stuck to the Spar will provide
calcium carbonate for smelting. 鈥淭hat will mean fewer trucks crossing the
Pennines from the limestone quarries in Cumbria,鈥� says McTeague.
The high-quality steel used to build the Spar is in demand, and there is a
growing shortage of scrap steel to supply a new generation of steel mills fed
solely by scrap. A couple of months ago, Lord Gregson, former chairman of an
engineering company and member of the House of Lords science and technology
committee, told a debate in the House of Lords that companies have even proposed
lifting old U-boats from the seabed to help meet demand. 鈥淭here is therefore a
strong case for recycling the steel from the offshore rigs,鈥� he said.
The British sector of the North Sea contains more than 200 rigs and an
estimated 10 000 kilometres of pipes. In a report published in March, the Lords
science and technology committee said that some 10 million tonnes of steel could
be brought ashore in the next few years, with a market value of around 拢3
billion.
Shell continues to argue that the Spar is unique. Structurally it is. But its
eventual disposal will set a precedent. And whether the ultimate choice is
turning it into a windmill for a Scottish island or cutting it up to feed the
booming market in scrap metal, environmentalists insist that it would be a big
improvement on sinking the wounded hulk at sea.
