Safety zones and decommissioning

Abstract

Australia’s oil and gas sector expects approximately 56 billion (AUD) to be expended for decommissioning costs over the next 50 years. The view of the National Offshore Petroleum Safety and Environmental Management Authority is that the designated decommissioning approach must provide equal or better environmental outcomes when compared to full removal of the infrastructure (considered the ‘best case’ expectation under current legislation) and meets as low as reasonably practicable (ALARP) levels of risk. Decommissioning alternatives are generally evaluated through a comparative multicriteria assessment approach, for example, a net environmental benefit analysis-based comparative assessment (NEBA-CA). Decommissioning options cover a range of possibilities, from full removal to leaving subsea structure in situ (in part or in whole). NEBA-CAs we have conducted suggest that some subsea structures are projected to generate significant ecological and social value over multiple generations to come. Thus, in these cases, management in situ can provide greater benefits to the public when compared to full removal. During operation, oil and gas assets typically incorporate a safety zone. If subsea structure is selected to be managed in situ, a question that arises is, should the safety zone be maintained or removed? Our experience indicates that if the safety zone is removed after decommissioning an asset that is left in situ, there may likely be a greater adverse impact on ecological and social values, depending upon the asset location. This abstract showcases the value of the use of safety zones to maximise environmental value while managing risk.