This paper describes the Ivanhoe/Rob Roy dynamic flexible riser system. The design requirements and considerations are summarised and a general description of the system is given. The paper then concentrates on giving details of the main components involved, thus presenting information on various aspects which are needed to turn theoretical knowledge and techniques into a viable system.


The Ivanhoe/Rob Roy floating production system has been operating successfully for around two years. A key part of that success has been the flexible riser system that links the floating production facility (designated AH001) with the subsea equipment.

The field is located in 140m of water approximately 140 kilometres north-east of Aberdeen. The field layout is shown in Figure I and consists of subsea wells located around the perimeter of two manifolds and joined to them with perimeter of two manifolds and joined to them with flexible jumpers. The manifolds are then connected to the Riser Base Manifold (RBM) by a further series of flexible flowlines about 1.6 kilometres long. The RBM is connected to the AH001 by the flexible riser system which thus allows for the passage of hydrocarbons from the wells to the passage of hydrocarbons from the wells to the platform and for export oil and gas, injection platform and for export oil and gas, injection water, and chemicals back to the seabed. Further descriptions and information on the field development are available.

Flexible dynamic risers have been used in various areas of the world including the North Sea and there are various papers on choice of configuration, analysis methods, etc.

The Ivanhoe/Rob Roy flexible riser system is shown in Figures 2 and 3. it is a lazy S configuration consisting of one 12 inch riser, one 10 inch riser, four 8 inch risers, two 5 inch risers and two chemical injection umbilicals, all rated at 3000 psi. This makes it one of the largest flexible riser systems in existence in terms of number and size of pipes and pressure rating.


The selection of the configuration and its layout started with the conceptual field design and underwent various stages of refinement. The basic sizes of the pipes was also determined at an early stage and subsequently refined by hydraulic analysis.

Various configurations are possible and in this case the 'Lazy S' configuration was adopted for the following general reasons:

  • compatibility with field layout

  • good performance characteristics

  • reasonable ease of installation.

The 'Lazy Wave' configuration (i.e. distributed buoyancy) was also a contender but there was insufficient space between the mooring legs to accommodate the required number of pipes.

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