What do you do with a worn-out oil rig?

Tom Heap

Decommissioning redundant oil rigs costs taxpayers billions. An alternative is to leave them in place to form artificial reefs, but is there an environmental price to pay?

Tom Heap explores these complex issues on board a North Sea oil platform which has been removed and taken to Norway to be completely recycled.

Several North Sea oil and gas fields are approaching the end of their commercial lives: as a consequence, the decommissioning of offshore platforms and the associated costs are looming on a scale not seen before, anywhere in the world. One of the first of these redundant platforms now stands at Veolia's decommissioning site at Lutelandet in South West Norway.

The platform is massive: covering an area of two football pitches, it's the size of a stadium on stilts; standing underneath, it feels like those sci-fi movie scenes when the vast, threatening spaceship hovers overhead. But this platform is just one of some 500 to 600 structures in the North Sea which will become redundant in the next few decades.

Removing the remains of our oil and gas industry is possibly the biggest clean-up job in the world.

Some scrubbing and dismantling has to be done at sea. But the rig on Lutelandet island was transported from the oil field – at considerable cost – using Pioneering Spirit: the biggest construction vessel in the world, a giant catamaran similar to two parallel oil tankers, designed for the single-lift installation and removal of large oil and gas platforms.

The decommissioning bill for the UK alone is currently estimated to be in the region of £50bn and, thanks to tax breaks offered to the oil companies, taxpayers will be paying more than half.

Drilling platforms resemble a compacted town made of steel. The supporting structure and pipework will all be recycled but other hardware like generators and cranes can be removed whole and reused, alongside equipment from the accommodation block like beds, kitchen equipment, a fully-equipped gymnasium and, in this case, a sauna...

Could the rig have been left at sea to become a home for birds and what lies beneath the waves – a habitat for fish? Engineers – some in the oil industry and growing numbers of environmentalists – are proposing that wells be capped and the structures cleaned, but then simply abandoned. It's well known that platform legs become encrusted with life, and old shipwrecks in the North Sea provide rare shelter on a largely featureless seabed.

In the Gulf of Mexico this approach, called "Rigs to reefs", has been normal practice for years and supporters claim that structures like submerged steel skyscrapers provide some of the most bio-diverse habitats in those waters.

Some environmental campaigners strongly oppose the idea, citing the principle that industry should clean up its own mess when it's finished. Current law states that only the bare minimum of redundant gear should remain on the sea floor.

Nearly 20 years ago Greenpeace won a memorable campaigning victory when their protest led to the reversal of a plan – supported by Shell and the government – to dump the oil storage buoy, Brent Spar, in the North East Atlantic. Today Greenpeace chief scientist Doug Parr says he rejects a future where "there is a default setting that dumping and using the marine environment as a place for stuff to be left lying around like rubbish becomes the norm".

But respected environmentalist and founder of Forum for the Future, Jonathan Porritt, says we risk using our money to remove valuable marine habitats: "There may be a better way of doing this that would create significant financial benefits for the taxpayer and significant ecological benefits."

Hear the full story in Costing the Earth on BBC Radio 4: Tuesday 14 February at 3.30pm or afterwards on iPlayer Radio.

Environmental programmes on the BBC