Exploring Uncertain Depths: Strategies for Deepwater Subsea Decommissioning in Navigating Unknown Structural Integrity

Abstract As global efforts toward energy transition intensify, the decommissioning of traditional oil and gas subsea assets becomes more prevalent. There are many challenges in dealing with aging subsea assets, particularly in determining their structural integrity. This paper aims to elucidate the challenges inherent in managing aging subsea infrastructure, with a specific focus on assessing structural integrity. By sharing insights from a decommissioning project, the paper seeks to outline an approach for navigating the uncertainties surrounding subsea structural integrity, emphasizing the criticality of assessing structural members—particularly lifting points—to ensure safe and efficient decommissioning. Retrieval of subsea infrastructure, although considered the reverse of installation, requires extensive effort and precise engineering to ensure that the operation meets its time, budget, and scope requirements. While visual inspections alone may not be sufficient to ascertain structural integrity, subsequent structural analyses conducted during the engineering phase are crucial for validating the condition of critical components. This analytical process also ensures that equipment can effectively withstand the loads encountered during lifting and retrieval activities. Readers can expect to gain comprehensive insights into the specialized tooling and methodologies used for subsea retrieval, including contingency strategies to address unforeseen challenges. While subsea infrastructure typically undergoes regular inspections throughout its operational lifespan, these assessments are often limited to visual inspections conducted by remotely operated vehicles (ROVs). Such inspections may not always detect underlying structural damage. Furthermore, if structural issues are identified but deemed non-threatening to safety or production during operations, they might not be fully restored to their original condition. However, during decommissioning endeavors, such as the retrieval of subsea structures, the condition of key structural components becomes paramount. Ensuring that these components are in optimal condition is imperative for the safe and efficient execution of decommissioning operations. This paper presents a comprehensive analysis of decommissioning and retrieval operations executed in a deepwater field, showcasing a paradigm shift in approach. It illuminates the novel retrieval methodologies adopted, tailored to the unique demands of abandonment and decommissioning (A&D) operations. The key to successful execution lies in identifying critical operations and addressing their associated risks. Adopting best practices and implementing prompt, decisive troubleshooting to manage the technical challenges encountered were essential factors for a successful campaign. By showcasing the efficacy of this approach in addressing unknown structural integrity issues during decommissioning projects, this paper contributes novel insights to the petroleum industry's knowledge base. The introduction of alternative methodologies, tailored to address retrieval challenges, establishes valuable precedents for future endeavors. While this approach may require additional vessel time, its proven success underscores its viability as a contingency option for similar projects, thereby enhancing industry practices and resilience in the face of evolving operational demands.