Optimization approach for sustainable decommissioning of unpiggable subsea pipelines: Insights from the Arabian Gulf.

Unpiggable pipelines, often inaccessible for traditional pigging operations, pose significant risks due to residual hydrocarbons and limited inspection options. This paper presents an optimized methodology for flushing, de-oiling, and abandoning unpiggable subsea pipelines, specifically designed to address the unique environmental and regulatory challenges in the Arabian Gulf. The paper introduces an innovative approach that integrates advanced modeling tools ‒ OLGA for internal flow assurance and CORMIX for pollutant dispersion analysis ‒ to manage oil-in-water (OIW) concentrations effectively, ensuring compliance with the stringent 15-ppm discharge limit. The proposed methodology not only mitigates residual contamination risks but also enhances operational efficiency and regulatory compliance through adaptive measures. By addressing plateauing contaminant removal rates and leveraging region-specific environmental data, the current study provides actionable guidance for sustainable decommissioning of subsea pipelines. The findings hold broad applicability for projects in environmentally sensitive marine ecosystems, hence, supporting global efforts toward environmentally responsible decommissioning practices.