A multi-criteria decision approach to decommissioning of offshore oil and gas structure

Abstract

Thousands of the world’s offshore oil and gas structures are approaching obsolescence and will require
decommissioning within the next decade. Many nations have blanket regulations requiring obsolete
structures to be removed, yet this option is unlikely to yield optimal environmental, societal and economic
outcomes in all situations. We propose that nations adopt a flexible approach that allows
decommissioning options to be selected from the full range of alternatives (including ‘rigs-to-reefs’
options) on a case-by-case basis. We outline a method of multi-criteria decision analysis (Multi-criteria
Approval, MA) for evaluating and comparing alternative decommissioning options across key selection
criteria, including environmental, financial, socioeconomic, and health and safety considerations. The MA
approach structures the decision problem, forces explicit consideration of trade-offs and directly involves
stakeholder groups in the decision process. We identify major decommissioning options and provide a
generic list of selection criteria for inclusion in the MA decision process. To deal with knowledge gaps
concerning environmental impacts of decommissioning, we suggest that expert opinion feed into the MA
approach until sufficient data become available. We conducted a limited trial of the MA decision
approach to demonstrate its application to a complex and controversial decommissioning scenario;
Platform Grace in southern California. The approach indicated, for this example, that the option ‘leave in
place intact’ would likely provide best environmental outcomes in the event of future decommissioning.
In summary, the MA approach will allow the environmental, social, and economic impacts of decommissioning
decisions to be assessed simultaneously in a transparent manner."