By Sam Phipps

With some 7,500 offshore rigs now in use around the world, and many of these nearing the end of their useful spans, the question of decommissioning is gaining urgency. However, despite international legislation stipulating complete deconstruction and removal, there is little consensus on best disposal methods.
Obsolete rigs may be exempt if they fulfil a “legitimate” purpose such as reef creation for biological conservation, and this has happened widely in the Gulf of Mexico, South-East Asia and Mexico.
Now a team of Australian scientists is exploring, from an ecological and biological perspective, whether rigs-to-reefs (RTR) could be viable in deep water too.
“We are interested in the potential effects, positive and negative, if you go and tow a structure to a drop zone in deeper water,” said Professor David Booth of the School of the Environment, University of Technology, Sydney (UTS).
 

Risks and rewards
At issue is whether such artificial reefs could enhance biological productivity, improve ecological “connectivity” between species and aid conservation/restoration of cold water corals by limiting access to fishing trawlers.
On the other hand, the risks include damage to existing benthic habitats in the drop zone, negative changes to marine food webs and unwitting support to invasive species – also, of course, the release of contaminants from corroding structures.
Ashley Fowler, a PhD candidate from the same faculty in Sydney, said extensive research was vital to give industry, regulators, fishermen and other stakeholders a better idea of these likely impacts. He will be making his case to delegates at the Decom World conference in Singapore in October.
“There are a lot of 'ifs' and 'maybes'. The reason further research hasn’t been done until now is the difficulty in accessing deep-sea habitats,” he said. “It’s very hard for us scientists to get out there, and also hard to [do research] work on structures that are as big as oil rigs.”
UTS is urging the oil and gas industry to contribute more funding to this area of research generally, on the grounds that its cost savings from deepwater rigs-to-reef schemes will be potentially significant.
It cites the global Serpent project (Scientific and Environmental ROV Partnership using Existing iNdustrial Technology) as one such successful collaboration between the industry and academics.
 

Depth of research
Among the many conundrums of artificial reefs is whether they boost fish populations by providing extra habitat, or whether observed increases in stocks are the result of “attraction”, i.e. the fish have merely settled from elsewhere. Attraction is usually seen as negative as it can concentrate resources and make them easier to exploit.
As for invasive species, rig relocation can spread these unless fouling or encrusting organisms are removed from surfaces beforehand. Even “clean” rigs could facilitate this spread by serving as stepping-stones for dispersal.
This issue needs to be considered case by case, depending on the organisms on a particular rig; the transport path to the new site; and the physical and biological conditions there, the UTS scientists say.
But they note that shore-based decommissioning still brings possible spread of invasive species via transport to coastal areas.
“As scientists, (A) we want to get it right and (B) it’s a great opportunity to understand more about the deep sea, of which we know so little,” Professor Booth said.
“You need several years of data, so it’s going to be a very economical thing to get these research programmes going at this stage rather than ‘quick, quick, quick – you’ve got a month to tell us where to put this thing.”
 

Questions of liability
Oil and gas operators also stand to enhance their profile by making deep-sea reefs that benefit the marine environment.
A legal counsel to a major operator in Malaysia, where there is one artificial reef in shallow water, said deepwater reefing was not yet on the radar. But it probably posed fewer socio-economic issues because it would not affect fishermen as directly as shallow reefing.
“Offshore we barely have any government guidelines on decommissioning full stop, much less on reefing. It is uncharted territory – we go on a case-by-case basis following international standards.
“I’m not saying deepwater rigs are not possible here, I just wonder whether it becomes a more cumbersome solution than scrapping rigs because of all the negotiations you have to go through with local authorities and so on. Liabilities could prove very complicated if it is not done properly.”
In summary, deep-sea RTR has a long way to go before it can be seen as a realistic solution. But if academic and industry minds continue to work together, it could become a key tool in global decommissioning.
 

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