This paper presents the repurposing of a non-insulated, carbon steel service line into a production line for a deep-water oil field, successfully carried out without any plant shutdowns and continued for several months and under several operating conditions.
The main differences between the repurposed service line and the subsea production lines of the field were the lack of insulation, to prevent hydrates during shutdowns and wax deposition during production, and the lack of internal cladding, to protect the line from generalized CO2 corrosion. Therefore, the conversion required deep multidisciplinary analyses, including flow assurance, production chemistry and materials technology, along with the definition of a proper continuous monitoring workflow.
The analyses started from a reservoir study to quantify the potential production increase and recovery factor due to the availability of the repurposed line, from some wells to the FPSO. After a positive outcome, a detailed flow assurance study was performed to select the wells to be routed to the service line and to define its operating conditions.
The laboratory identification of the most effective wax inhibitor and hydrates anti-agglomerant was conducted, together with a corrosion study to estimate the life span of the carbon steel line to be repurposed. The lack of subsea chemical injection umbilical lines was addressed by identifying a combo product with both hydrate and corrosion inhibitor functionalities.
All the above studies were associated to the definition of a strict monitoring workflow of the line corrosion and performance, in terms of potential restriction due to deposits.
The overall techno-economic analysis demonstrated the feasibility and benefits of the production mode achievable with the repurposed line, even at higher operating costs. Consequently, the conversion was successfully carried out and is now effectively in place since more than one year.
The whole study also strongly benefitted by the critical re-evaluation of all the engineering and operating margins made possible by the data acquired and recorded by Eni’s digital oilfield e-DOF system.
