The BP Angola Programme focuses on the development of a number of deepwater oil production projects within the Angolan Offshore Block 31 and 18. PSVM is the first field under development within Angola Offshore Block 31 and uses a centrally located FPSO with subsea ‘offline’ manifolds and clustered wells located in water depths up to a maximum design of 2100m. The extensive production flowline system features three "hybrid loops", compromised of highly insulated pipe-in-pipe production flowlines, with the remote end linked to the host FPSO by a single wall service flowline for dead oil displacement and inspection pigging.
During the design, a number of technical challenges were identified, requiring collaborative approaches and complex numerical analysis to develop a robust final solution. These challenges included balancing the effects of sour produced fluids and slug flow on fatigue strength, with the thermo-mechanical design including buckling and walking mitigation. The combination of a heavy pipe-in-pipe cross section and very soft seabed soils further complicated the design. The buckling design solutions developed were compatible with installation in 2km water depth, used proven and qualified methods and materials and ensured integrity for the 25 year design life.
This paper outlines the approach to thermal expansion management through engineered lateral buckles. The selection of buoyancy sections in preference to sleeper arrangements, which have been popular in the past, are explained.
The main features of the final design are described, including procurement, construction and installation considerations. Observed buckling response from commissioning and early production is compared with design predictions, and key lessons learnt are shared.
The paper seeks to demonstrate the merits of buoyancy modules in preference to sleepers as buckle mitigation devices for deepwater flowlines. Key design considerations are identified, and a rational design process consistent with SAFEBUCK and DNV guidance is outlined.