Understanding the trade-offs

Lara Alvarez analyses the value of flexibility in oil and gas decommissioning

With the marine environment facing intensifying pressures from climate change, waste and resource management, and habitat destruction, and as the debate on the drivers of the OSPAR Convention reignites, is it time to take a more holistic approach and assess the sustainability of offshore infrastructure decommissioning? In pursuing its ambition to become a global leader in decommissioning oil and gas installations and mature field management, the UK government should evaluate the range of options that address environmental responsibility and deliver best value for money.

The UK is one of the largest and fastest growing markets by value in offshore decommissioning, with almost one million tonnes of oil and gas installations, pipelines and underwater assets to be removed within the next seven years. As it currently stands, EU nations are implementing a policy of complete removal of all offsstructural elements of offshore oil and gas platforms. However, scientific evidence suggests that the total removal of such structures can in fact have negative consequences to valuable marine ecosystems.

Not only does it pose a huge technical challenge, but the financial upshots of these plans are equally astounding, with the Oil & Gas Authority and HM Revenue and Customs approximating costs of £61 billion for operations. As for taxpayers, an additional sum of £24 billion has been estimated, owing to high-tax deductible expenditures.

In addition to costs and technical barriers, the physical scale of the decommissioning process demands trade-offs between a range of other factors including: engineer safety; disturbing or removing habitats and the marine life they support; reducing biological connectivity between platforms; re-opening areas for bottom fishing; mobilising buried contamination; and the carbon footprint of air emissions associated with the removal of piled structures.

Such a vast array of considerations has meant that the number of scientific publications aimed at improving the understanding of the impact of removing these man-made structures in the North Sea has grown at pace, supported by research programmes such as INSITE.

Initial results are in line with the findings from more extensive research conducted in other jurisdictions such as the Gulf of Mexico and California, and there now seems to be a wider Decom 178 bunderstanding that failure to consider the negative impacts associated with offshore decommissioning in the North Sea could have extremely damaging effects on marine ecosystems. Many of these North Sea installations have been in place for over 30 years and have established communities, including protected cold-water coral species attached to structures and mobile organisms (such as crustaceans and fish) that utilise the different ecological niches provided by these structurally complex habitats for feeding or reproduction. The increase in seafloor heterogeneity and the provision of a safe zone that attracts fish and supports the recruitment and growth of larvae and pelagic juveniles ultimately enhances fisheries.

Offshore platforms can also support the conservation and restoration of the benthos and reduce fish over-exploitation through their exclusion zones, which bar fishing and other activities from the area. The loss of access and displaced fishing effort for fishermen can be partially compensated by the increased fish production rate when overspill effects occur outside of the exclusion zones, reducing the catch per unit effort associated with the harvest of commercial fish species. Some researchers are therefore promoting the use of exclusion zones as a tool to assist the management of marine resources, together with ‘total allowable catches’ or fishing closures. Evidence also indicates that some installations constitute a network of artificial reefs, and are biologically connected, placing the aggregate habitat value and associated productivity of the network higher than that of its individual structures.

Despite this evidence, the UK government continues to enforce a clean seabed policy in line with OSPAR Decision 98/3, which prohibits leaving the installation on the seabed (partially or entirely) and demands a return to its ‘natural state’ upon decommissioning. This policy assumes that man-made structures have lower ecological value than the pre-installation seafloor habitat and lacks flexibility in decommissioning strategies. Derogation from full removal is solely based on technical criteria and, as such, may not be granted.

The increasing scientific evidence on the unintended consequences of offshore decommissioning, coupled with the growing intensity of decommissioning efforts and large investment programmes should position the UK as the global leader in sustainable decommissioning. R&D focused on transforming the conventional approach to decommissioning, plus cost reduction for taxpayers and the oil and gas industry, is resulting in much-needed debate on decommissioning approaches across the UK Continental Shelf. On the back of these developments, the UK has a unique opportunity to examine the impact of large-scale decommissioning on the long-term sustainability of marine ecosystems.

If we are to truly protect the environment, the complexity and variety in designs, installations and operations of individual oil and gas structures must be reflected in a flexible policy that allows for tailored solutions for each platform and seeks a wider understanding of the unintended consequences of full removal. Importantly, this flexible approach in no way constitutes a license to pollute as measures aimed at ensuring the safe abandonment of the installation, such as flushing of pipelines, would be incorporated in a viable decommissioning option. In fact, a well-designed decommissioning strategy would identify and minimise unintended consequences to the environment – particularly important given the extensive pressures impacting marine ecosystems at present, including depletion of fish stocks on the seafloor, loss of habitat and further ecosystem components under conventional fishery management, and changes to ocean circulation and stratification induced by climate change.

The analysis of decommissioning alternatives for each individual structure should be based on a transparent assessment, utilising robust scientific approaches such as resource or habitat equivalency analysis, the Green Book Value-for-Money framework, and net environmental benefit analysis (NEBA) underpinned by ecosystem services frameworks. Critically, the range of costs, benefits and wider impacts of the various decommissioning options should be identified and the trade-off should be clearly presented. This will ensure that the net environmental and socio-economic impacts are analysed alongside technical, cost and safety criteria, facilitating a well-balanced decision for an individual platform as part of a wider collection of biologically-connected offshore installations.

Ultimately, how the government decides to approach the decommissioning of oil and gas platforms will set an example for a range of newer offshore infrastructures such as wind turbines, which will require decommissioning in the near future. Keeping tabs on circularity, design, installation and end-of-life considerations of new infrastructure will ensure we have learnt from the oil and gas industry, and fully incorporating them into the early project planning phases will hopefully enhance the habitat value of the structures in the marine environment, minimising disturbance to the ecosystem.

Lara Alvarez is Managing Consultant at Ramboll. Ramboll is a leading engineering, design and consultancy company founded in Denmark in 1945. With 300 offices in 35 countries, Ramboll combines local experience with a global knowledgebase constantly striving to achieve inspiring and exacting solutions that make a genuine difference to clients, end-users, and society. Ramboll works across a range of markets, including Environment & Health, Energy, Buildings and Transport. For further information please visit: https://uk.ramboll.com/