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Abandoned oil rigs

A new lease of life!

Photograph: iStock

Text: Mariano Anthony Davies

Marine biologists have discovered that abandoned offshore oil rigs are proving to be better nurseries for some fish species as the towering under water pylons seem to be perfect spawning grounds for tiny fish larvae.

There are more than 12,000 offshore oil and gas platforms worldwide. As they drain their reservoirs of fossil fuels below the sea, they eventually become defunct when they produce too little fuel for extraction to be profitable to their operators.

The big question is what to do with these enormous structures when fossil fuels stop flowing. With curbing climate change increasingly on the international agenda, and with many questioning whether the importance of oil is actually diminishing, the number of defunct rigs in the ocean is bound to increase.

There are two hugely conflicting points of view in this global environmental debate. Some argue that removing them from the water is incredibly expensive and labour-intensive, while others would argue that allowing them to rust and fall into disrepair is an environmental risk that could seriously damage marine ecosystems.

Removal is typically undertaken in two stages. First, the topsides equipment is cleaned and broken into sections for lifting onto crane barges or, for heavier topsides structures, a double-hulled tanker. Once the topsides have been removed, the jacket is cut, lifted onto a barge and both topsides and jacket are taken onshore for dismantling and recycling.

The dilemma is that oil and gas wells always need to be plugged to prevent the abandoned hydrocarbon reservoir's contents from leaking into the surrounding environment. This needs to be balanced against ever-growing evidence that leaving the jacket and topside structures in the sea can be environmentally positive.

Take the case of the lophelia coral. This is a good case for those that would argue that the abandoned oil rigs are less of an environmental risk being left where they are. It is a stony coral that lives in the deep sea rather than on shallow, tropical coral reefs and like all corals, this species is closely related to anemones, jellyfishes and other animals in the Phylum Cnidaria (11.000 species of aquatic animals).

“According to a team of researchers from Aarhus University in Denmark, turning abandoned oil rig towers into reefs may prove a less expensive and more environmentally friendly way to retire or reuse these aging oil platforms.”

Unlike shallow-water corals, lophelia corals and other deep-water corals do not get their food from symbiotic algae living inside their cells. Instead, they are filter feeders and obtain all of their energy by picking individual plankton from the water that flows along deep-sea currents.

Not only can this type of coral build structures that provides habitat for many kinds of invertebrates and fishes, but scientists also suspect that these coral reefs may be tens of thousands of years old and slow-growing - potentially living for more than 1000 years. This species is typically found down to depths of approximately 1000 metres, but it has also been observed or collected from depths of nearly 3000 metres.

Lophelia coral builds a skeleton of calcium carbonate – a compound that will decrease rapidly as the ocean acidifies. As deep water is naturally more acidic than shallow water, deep-water corals are particularly vulnerable to this problem. Unless we cut our carbon dioxide emissions, scientists predict the waters in which deep-water corals live may eventually become acidic enough to literally dissolve their skeletons. Acidification not only risks the survival of this and other corals but also the high numbers of other species that rely on coral reef structure as their main habitat.

The oceans are potentially facing an oil rig challenge. The North Sea alone has about 600 platforms and more than 7,000 wells to decommission and many of these are in deep water. Some of them weigh up to 330.000 tons. Dismantling would be a massive challenge.

According to a team of researchers from Aarhus University in Denmark, turning abandoned oil rig towers into reefs may prove a less expensive and more environmentally friendly way to retire or reuse these aging oil platforms. Rather than removing the structure, these scientists (along with many of their colleagues worldwide) suggest that converting towers into artificial ocean reefs would provide safe living and spawning grounds for ocean creatures.

Denmark is looking towards marine biology to solve a massive oil rig challenge and at the same time, expects to remediate some of the country's environmental problems.

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