Optimised Light Weight P&A Well Access Solution

Abstract As offshore oil and gas fields mature, a growing number of subsea wells are reaching the end of their productive life. This shift has placed decommissioning—and particularly plug and abandonment (P&A)—at the forefront of the industry’s agenda. With increasing regulatory scrutiny, environmental considerations, and the need to reduce long-term liabilities, operators are under pressure to find innovative, safe, and cost-effective solutions for decommissioning aging subsea assets. Recognizing this need, we developed the world’s first dedicated lightweight, compact Plug and Abandonment Open Water Bore Selector Well Access Riser-based System. This pioneering system was designed in close collaboration with a North Sea operator to address a highly specific and technically challenging requirement: the plug and abandonment of a triple bore completion—a rare and complex well architecture, believed to be the last of its kind globally. The system was engineered with a modular and scalable design, enabling it to be adapted for use on conventional dual bore completions as well. This flexibility ensures that the system can be redeployed across a wide range of well types, maximizing its value and utility. It is also compatible with Mobile Offshore Drilling Units (MODUs), further enhancing its operational versatility. In addition to its bore selector capabilities, the system was specifically designed to address the challenges posed by aging and structurally fatigued wellheads. This is particularly relevant in the UK North Sea, where the average age of subsea infrastructure now exceeds 25 years, increasing the risk of integrity issues during intervention and abandonment operations. The initial contract for this system was awarded in 2019, following a successful conceptual design phase in partnership with our client. The scope included a three-well P&A campaign in the North Sea. The system was fully designed, manufactured, and underwent successful System Integration Testing (SIT). However, the project was temporarily deferred due to the global COVID-19 pandemic, which caused widespread delays across the offshore energy sector. Following the resumption of offshore activities, our client awarded a follow-up contract in 2024 for a significantly expanded campaign involving the plug and abandonment of 33 subsea wells. This new scope reflected the cessation of production in additional subsea fields and included the final triple bore well, with the remaining wells consisting of conventional dual bore Vertical Xmas Trees. System was mobilized in January 2025 and has since been deployed successfully in the field. To date, it has completed the plug and abandonment of six subsea wells, demonstrating its effectiveness across both triple and dual bore configurations. The system’s performance has validated its design principles and confirmed its potential for broader application in future decommissioning campaigns. This project represents a significant step forward in the evolution of subsea P&A technology, offering a cost-efficient, safe, and adaptable solution to one of the industry’s most pressing challenges. By combining engineering innovation, collaborative development, and operational flexibility, we are helping to shape the future of responsible offshore decommissioning.