Decommissioning of offshore oil and gas structures - Environmental opportunities and challenges.

Thousands of offshore oil and gas structures are approaching the end of their operating life globally, yet our understanding of the environmental effects of different decommissioning strategies is incomplete. Past focus on a narrow set of criteria has limited evaluation of decommissioning effects, restricting decommissioning options in most regions. We broadly review the environmental effects of decommissioning, analyse case studies, and outline analytical approaches that can advance our understanding of ecological dynamics on oil and gas structures. We find that ecosystem functions and services increase with the age of the structure and vary with geographical setting, such that decommissioning decisions need to take an ecosystem approach that considers their broader habitat and biodiversity values. Alignment of decommissioning assessment priorities among regulators and how they are evaluated, will reduce the likelihood of variable and sub-optimal decommissioning decisions. Ultimately, the range of allowable decommissioning options must be expanded to optimise the environmental outcomes of decommissioning across the broad range of ecosystems in which platforms are located.