A framework for a net environmental benefit analysis based comparative assessment of decommissioning options for anthropogenic subsea structures: A North Sea case study

Abstract

Taxpayers and operators worldwide have significant current liabilities associated with decommissioning of offshore Oil & Gas (O&G) assets. Consequently, decommissioning is at the forefront of industrial, governmental, and non-governmental agendas. Decommissioning is a highly complex activity with health, safety, environmental, social, economic, and technical implications. Increasing scientific evidence supports that manmade subsea structures create hard, artificial reef habitats that provide ecological and social benefits to society. Given the significant uncertainty regarding how subsea structures should be retired at the end of their operational lifetimes, it is necessary for governments, taxpayers, and operators to understand the risks and benefits associated with potential decommissioning options. Currently, the North Sea decommissioning process is based on the policies and direction of the Oslo and Paris Convention’s (OSPAR) Decision 98/3 and follow comparative assessment (CA) multiple-criteria decision analysis (MCDA) guidelines to determine the best overall strategy for decommissioning subsea structures; however, CA MCDA processes can be biased, ambiguous, difficult to use, interpret, and replicate, and limited in their consideration of multigenerational benefits. Consequently, to assist decision-makers in understanding and evaluating options and associated benefits for decommissioning subsea structures, this study adapted the net environmental benefit analysis (NEBA) framework to supplement and strengthen the CA process for evaluating decommissioning options for offshore O&G facilities. The net environmental benefit analysis based comparative assessment (NEBA-CA) framework is presented that addresses the growing need for a practical, quantitative, scientifically robust, defendable, and transparent MCDA approach to determine optimized decommissioning strategies for subsea assets. Increased transparency in CAs will provide an additional layer of credibility with regulators and society. The approach is data driven and a desktop analysis mainly relying on existing data. Using a North Sea case study, this work demonstrates the ability of NEBA-CA to resolve inherent complexity in comparing decommissioning options, thereby supporting operators in working with regulators to decommission assets in a way that maximizes ecosystem service benefits to society while managing site-related risks and costs. The NEBA-CA framework supplements and strengthens the standard CA process by 1) incorporating quantified metrics including multigenerational ecosystem service benefits and risks, 2) excluding front ranking (scoring) or weighting of metrics, and 3) providing consistent graphical displays to support visual differentiation of options and metrics.

Offshore Decommissioning Horizon Scan: Research Priorities to Support Decision-Making Activities for Oil and Gas Infrastructure

“…Industry also calculates costs of alternative approaches, such as relocating structures to a reefing location. These assets have the potential to provide a variety of economic benefits to society for hundreds of years, delivering a multi-generational flow of ecosystem service value over this period (e.g., Nicolette et al, 2023). However, ongoing, and longer-term economic impacts and benefits also need to be determined and considered within the offshore decommissioning decision-making process comparing full life cycle costs of an onshore disposal option against such alternative options.…”

“…Given the breadth of ecosystem services associated with offshore habitats (Barbier, 2017;Layman and Allgeier, 2020;Buonocore et al, 2021), understanding the key metrics that differentiate between decommissioning options is essential (Nicolette et al, 2013b). In some arenas, e.g., Natural Resource Damage Assessments (NRDA) in the U.S. (Nicolette et al, 2023; although not a tool specifically for decommissioning), surrogate/proxy metrics are identified by stakeholders that reflect the flow of habitatbased ecosystem services and are used to evaluate changes in value over time (Efroymson et al, 2004). A net environmental benefit analysis (NEBA) comparative assessment approach has recently been adapted to offshore decommissioning (Nicolette et al, 2023), and related analyses have been applied to subsea structure decommissioning option decision making for sites in Australia, California, Caribbean, Gulf of Mexico, Gulf of Thailand, and the North Sea (IOGP, 2022;Nicolette et al, 2023).…”

“…In some arenas, e.g., Natural Resource Damage Assessments (NRDA) in the U.S. (Nicolette et al, 2023; although not a tool specifically for decommissioning), surrogate/proxy metrics are identified by stakeholders that reflect the flow of habitatbased ecosystem services and are used to evaluate changes in value over time (Efroymson et al, 2004). A net environmental benefit analysis (NEBA) comparative assessment approach has recently been adapted to offshore decommissioning (Nicolette et al, 2023), and related analyses have been applied to subsea structure decommissioning option decision making for sites in Australia, California, Caribbean, Gulf of Mexico, Gulf of Thailand, and the North Sea (IOGP, 2022;Nicolette et al, 2023). Use of surrogate/proxy metrics, within a service-to-service approach to represent the overall flow of ecosystem services, has been applied to support decision making for damage-assessment cases in the United States (Chapman et al, 1998;Chapman and LeJeune, 2007;Nicolette et al, 2013bNicolette et al, , 2023.…”

“…A net environmental benefit analysis (NEBA) comparative assessment approach has recently been adapted to offshore decommissioning (Nicolette et al, 2023), and related analyses have been applied to subsea structure decommissioning option decision making for sites in Australia, California, Caribbean, Gulf of Mexico, Gulf of Thailand, and the North Sea (IOGP, 2022;Nicolette et al, 2023). Use of surrogate/proxy metrics, within a service-to-service approach to represent the overall flow of ecosystem services, has been applied to support decision making for damage-assessment cases in the United States (Chapman et al, 1998;Chapman and LeJeune, 2007;Nicolette et al, 2013bNicolette et al, , 2023. The European Union Environmental Liabilities Directive (EU ELD) also gives preference to service-service approaches in evaluating resource injury and compensatory restoration (Nicolette et al, 2013a).…”

“…2), and there is also a growing body of evidence supporting environmental and societal benefits of leaving the established ecosystems that have developed around such infrastructure within the marine environment post its operational use (Fortune and Paterson, 2020;Fowler et al, 2020;Schläppy et al, 2021;Elrick-Barr et al, 2022). These benefits need to be weighed against the potential for negative impacts, including infringement on other marine users, contaminants released to the marine environment, and liability issues associated with the ongoing maintenance and responsibility for re-used infrastructure (Nicolette et al, 2023).…”