Case studies of clustering of decommissioning activities for subsea systems with manifolds

Abstract

The decommissioning of subsea systems in mature offshore fields represents a critical and complex stage, requiring rigorous technical planning, integrated risk management, and environmental compliance. Carrying out decommissioning immediately after production shutdown (late life stage) tends to present lower complexity and cost. In particular, wells connected to manifolds pose additional challenges for activities related to pipeline cleaning and disconnection/plugging. In this context, the strategy of grouping decommissioning activities and resources emerges as an efficient solution to mitigate operational and environmental risks, increase operational efficiency, avoid rework, and reduce costs associated with decommissioning. Two case studies of subsea systems will be explored in this article, involving production manifolds that have not produced for several years, named manifolds X and Y, both located in a mature production field. This strategy consists of sequentially and integratively grouping well abandonment, pipeline cleaning, and pipeline disconnection/plugging activities, considering the integrity condition of the subsea systems and their interconnection with the floating platform. It is concluded that this strategy can be replicated, accelerating industry learning and contributing to the adoption of best practices in the offshore decommissioning industry in Brazil.