NEBA Application for Offshore Subsea Pipeline Decommissioning

Abstract

There is a demonstrated need for both technical and non-technical factors of the decommissioning industry which are the criteria of decision making in decommissioning project development. In Gulf of Thailand, there are huge numbers and volumes of offshore subsea pipelines expected to be decommissioned when the concession is end. The evaluation of pipeline decommissioning technique to determine the optimum final project configuration to reflect the long-term environmental impact or benefit of various decommissioning techniques is required. Therefore, the innovative model "Net Environmental Benefit Analysis (NEBA)" was applied to determine the environmentally project alternative. NEBA model provides a relative ranking on the expected environmental values of project alternatives which based on outcomes of a consensus workshop among stakeholders and regulators which was arranged to obtain final agreement on environmental values identification, weighting and scoring of project. The semi-quantitative NEBA model used here is structured around the determination of the functional elements of the NEBA: the service impact level, recovery period, post recovery services value, and post-recovery period. This study focus of NEBA is to determine the net benfit for seven different decommissioning techniques for offshore subsea pipelines based on a specific ecological services of the project producing an impact. For the purpose of this study, ten ecological services were evaluated for each decommssioning technique (i.e habitat value, production value and behavioral responses). The mathematics in this model is developed around the service metric gains and losses and considered to be semi-quantitative since the criterion rankings and relatively with respect to baseline are based on the agreement of the workshop. Finally, the quantitative NEBA score in the context of the clear environmental benefit and impact in each technique was provided to a decommssioning project development decision maker to make defensible decisions to choose the most appropriate cost effective decommssioning technique to company.