North Sea decommissioning is finally happening and it means some difficult questions are starting to be asked about what should be left behind and what might benefit sea life. Elaine Maslin explores the details.
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Shoal of Pollock (Pollachius pollachius) around the BOP at Hurricane Energy’s Lancaster well at 150m water depth west of Shetland. Photo from A.Gates, SERPENT Project in collaboration with Hurricane Energy. |
After, in some cases more than 40 years of service in the cold harsh waters of the North Sea, oil and gas production facilities are starting to be shut-in and removed.
But, while the rules effectively state everything needs to be removed from the sea, with the option to leave certain structures in place, more and more people within and outside the industry believe that removing the rest of them might not be the best thing to do.
Tom Baxter, senior lecturer in chemical engineering, at the University of Aberdeen, for example, says, while the need for plugging and abandonment is not in dispute, some suggest that removal activities will cause more damage than good. He says that this indicates that, “at the very least, the environmental case for decommissioning is not compelling,” especially as UK taxpayer cash will help fund a sizeable proportion of the cost of removal and remediation.
Others make a more philosophical case. Based on the leaving behind a “clean seabed” ethos, and given there’s been 50 years of exploration and production activity, “What is the North Sea’s pristine condition? How do we get it back to that state? And would that really be the best thing to do,” asked three University of Aberdeen professors in a joint article, published late 2016.
Being a largely sand and mud-bottom basin, manmade structures, such as platforms and substructures (1300 of them across Europe, plus about 1800 and increasing number of wind turbines, thousands of buoys and some 25,000 recorded wrecks on the seafloor*), offer scant havens for some species that like hard things to cling on to, it is suggested.
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European Conger (Conger conger) in a structure at the seabed at Hurricane Energy’s Whirlwind well at 180m depth west of Shetland. Photo from A.Gates, SERPENT Project in collaboration |
The problem is, there’s been little by way of robust scientific evidence to show if these structures, often originally put in place without much thought towards how they would be removed, benefit – or otherwise – marine life.
That’s changing. As well as Engie E&P’s proposal to leave in place two small southern North Sea jackets, there is a significant research program underway involving scientists and researchers from across the UK. The Insite Program is seeking to assess the impact of manmade structures – platforms and windfarms – on marine life, both individually but also as a network, i.e. as stepping stones for marine life.
It is sponsored by eight oil companies, but their cash is given to research projects through an Independent Scientific Advisory Board (ISAB), which also manages the research objectives and encourages the researchers to publish their findings. The research projects formally started in Q4 2015 and will run until Q4 this year.
Three of the projects are about quantifying the effects, two are about connectivity and three address both. The projects, while independent, are being run to create a coherent package. Some of the initial work was presented at an event – the Insite Science Day at Imperial College London – attended by staff from the likes of Shell, Chevron, Repsol, and Eni, late 2016.
While it’s too early into the project to give any conclusive results, the work will help lay the ground work for a better understanding in this area.
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A map of mapped wreck sites in the North Sea. Photo from Wrecks.eu. |
The Coupled Spatial Modeling (COSM) project, for one, will help build a modeling tool that could be used to assess sites. Chris Lynam, who works at the Centre for Environment, Fisheries and Aquaculture Science (CEFAS), says that the tool will model the consequences of existing manmade structures on the “food web” and biomass. The project involves collecting a lot of data about what benthic groups (flora and fauna on the seabed), fish groups and even plankton exist and where, including bathymetry, depth, salinity, etc. Seabird and mammal movements are also due to be added into the model, including where they travel and forage.
“The North Sea is mostly sand, then mud beds,” Lynam points out. ”There is not a lot of rocky substrate. Manmade structures could be the main substrate out there. An interesting thing is comparing the other manmade structures (such as shipwrecks, many being wooden) to oil structures. There are an awful lot of things going on we need to consider and perhaps more than we anticipated.”
Prof. Murray Roberts, from the University of Edinburgh, is working on a project called ANChor (Appraisal of Network Connectivity between North Sea oil and gas platforms) in collaboration with Heriot-Watt University, University of Liverpool and BMT Cordah. The idea is to see if platforms connect species and ecosystems across the North Sea. It is doing this by looking at larva from various species which live around platforms and then simulating where they could travel to and what would happen if the nodes (platforms) that they travel to were removed.
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Cod (Gadun morhua) and a sea urchin on a protective structure at Hurricane Energy’s Lancaster well at 150m water depth west of Shetland. Photo from A.Gates, SERPENT Project in collaboration with Hurricane Energy. |
The work means creating a GIS database of platform-based marine growth data – i.e. what and how many creatures live on offshore platforms. Instead of collecting data from all 487 installations, they’ve got data from 57 (15 in the northern North Sea, 10 in the central North Sea and 32 in the southern basin). They’ve also drawn on industry ROV surveys dating from 1981 to 2015, as well as other published data. As expected, species like deepwater corals are more likely to appear on the deeper water platforms in the northern sector.
Work to create larvae dispersal simulations in a 3D, 1.8km horizontal resolution model is ongoing, but studies have already shown they could travel hundreds of kilometers in just over a month. While it’s early days, and the influence of pipeline infrastructure on connectivity hasn’t yet been included, “it’s suggesting to us there is some pretty good connection between some of these structures,” Roberts says. “The platforms do have a very important role and I think this work will be fundamental in other projects. We might consider that organisms on platforms might have value in their own right. Could they be used to help restore other areas?”
Kieran Hyder, also from CEFAS, is also looking at connectivity, specifically between areas of hard substrate, such as platforms and wrecks. As well as tracking larvae, they’ll look at how shipping movements could influence the marine life movement. Hyder says that what the structure is made of, i.e. concrete, steel or fiberglass, and how it is managed – i.e. if the legs are regularly cleaned – will also have an impact on whether marine life is supported.
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Piles on a research platform, 30km offshore Germany, in 30m water depth. One shows the upper part (0-10m depth) of the platform with blue mussels, amphipods and common starfish. |
Historic data is also used to see what the impact has already been. A long running project, called Signal, is drawing on data from a continuous plankton recorder survey, which has been running for 60 years, and offers a reference case for before oil platforms were installed. The project currently has its plankton recorder devices dangling off the back of 32 ships of opportunity, covering some 12,000km a month.
“There is evidence of a large scale move north of the zooplankton community,” says Willie Wilson, of the Sir Alister Hardy Foundation for Ocean Science (named after the man who started the plankton survey). “This has a knock-on effect for commercial fisheries,” he suggests. A cold water species like cod have fallen in numbers while a warm water less nutritious species have started to dominate, since 1985, he says. The question is, has this been caused by manmade structures? It could actually be more to do with the sea surface temperature, which has been warming and – in the last few years – starting to cool again and cold water species increase, while the number of manmade structures hasn’t fallen. More research needs to be done.
Also, just because there is more marine life, thanks to the platforms’ existence, is it good? Or could it promote invasive species? Under the Reefing Effects of structures in the North Sea: Islands or networks (RECON) project, Joop Coolen, Wageningen Marine Research, is researching what grows where in order to predict what will grow in certain locations – depending on various factors including temperature, depth, current velocity and salinity, and to see if different locations can be connected. He’s been out taking samples from platforms offshore the Netherlands (with permission) using a kind of subsea hoover, with plans to do the same off Norway and Denmark next, to map species distribution. “With this data we can try to predict what might populate a platform,” and looking at what are invasive and what are native species.
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The second shows fish that tend to accumulate around hard substrate. |
Jennifer Dannheim, from the German-based Alfred-Wegener Institut (AWI), is looking at a similar issue – the impact of structures in soft sediment areas. “When you introduce a structure in to a soft bottom [environment] it is really a different habitat, so there’s a fundamental difference in fauna between these habitats,” she says.
It’s a highly complex environment and there are more related Insite Program projects running than OE can outline here. Some appear to duplicate certain work, but this will improve the robustness of the results, says Prof. John Shephard, who sits on the ISAB board. The impact on the fisheries will be a further important topic, especially given the fisheries were long active before the oil industry came to town and will be active for a long time after it’s gone.
And, at this stage the research is more about gathering and understanding data. Coolen says that the work would be helped if operators gave more access to structures, even if it is just ROV footage, to help species mapping, a call repeated by Shepherd. Indeed, at the event, CNR International’s Roy Aspden offered to allow access to the Murchison jacket as it is removed, to aid the researcher’s work. Researchers and scientists will also be given access to the platforms Engie plans to leave in place, which will further aid their work. The work in the Netherlands might even help government efforts there to reintroduce the flat oyster, a species which once proliferated in their sector of the North Sea, but has since disappeared.
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Piles with fouling community that develops on the deeper part of structures, such as anemones, other cnidaria and blue mussels. Photo from Roland Krone, AWI. |
“We have a complicated issue that we don’t really understand,” Shepherd says. “The scope of work that is being done [under Insite], from larval behavior to the net benefit of a rig being there is important, because we don’t yet know where in this whole complex picture the important factors are going to be. We can be confident that there is no simple answer to the question ‘is rigs to reef a good thing to do?’ There will be positives and negatives and we will have to work out what the overall net effect is.”
In all likelihood, the result will be judged on a case-by-case basis, taking into consideration the wider ecosystem, with the help of the knowledge created by the Insite Program.
To find out more about the Insite Program and to view the Insite Science Day presentations, please visit: www.insitenorthsea.org.
*According to Joop Coolen, Wageningen Marine Research.
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