FPSO Riser Selection: A Journey from the Seabed to the Surface

Selecting an optimal riser concept for Floating Production, Storage, and Offloading (FPSO) vessels stationed in deep water presents significant challenges. The high hydrostatic pressure and large vessel payload directly impact the choice of riser system. Geographical location and prevailing weather conditions further influence this decision. For instance, while free-hanging flexible risers have found favor in the moderate environments of offshore Brazil, concepts like Steel Catenary Risers (SCRs) and Hybrid Riser Towers (HRTs) dominate in the calm weather conditions of the West of Africa (WoA). However, recommending a suitable riser concept for an FPSO stationed in the harsh environmental conditions like the Northern Norwegian Sea remains a daunting task. The vessel offsets and dynamics in this region directly transfer along the riser length, causing considerable fatigue damage. In this article author will present at glance the general type of riser technology including their advantages and challenges.

At the start, what is the FPSO Riser? Risers are vertical pipelines that connect subsea equipment (such as wellheads, manifolds, and flowlines) to the floating production unit (FPSO in this case). They play a crucial role in conveying fluids (oil, gas, and water) to and from the vessel. Riser is a part which act as transition between the offshore pipelines and the topside on board of the FPSO. The top part attached to the FPSO normally being design and built by the FPSO while the hanging part up the seabed are design and installed by the Pipeline package.

Let’s go deeper to talk about the type of each FPSO riser technology that currently utilized within the industry in general as follow,

1.       Steel Catenary Riser (SCR)

SCR consists of steel pipes that hang in a catenary shape from the FPSO to the seabed. They are tensioned to minimize vessel movement effects. Steel catenary risers are the conventional design of riser which are popular within the offshore installation. The steel catenary riser is continuously developed by the industry for answering the technical challenges of the recent development. On top of the initial simple catenary riser design, their improved concept such as Step Wave Riser and Lazy Wave Catenary Riser are introduced and applied within FPSO or other offshore facilities.

The list of advantage and challenges for the steel catenary riser can be summarized on the table below,

2.       Flexible Riser

Flexible risers are made of reinforced flexible pipes that can bend and move with the FPSO’s motion. They are suitable for Deepwater applications where vessel movement is significant. A flexible riser is a configurable product made up of several layers, each serving a specific purpose. The modular construction allows each layer to be independently adjusted to meet specific field development requirements. Apart from the hydrocarbon containment line (usually called Carcass), the flexible riser will have Leakproof Thermoplastic Barriers which normally construct from common thermoplastic materials such as polyethylene (PE), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE). And Corrosion-Resistant Steel Wires from helically wound steel wires which provide the structure’s high-pressure resistance and excellent bending characteristics.

The list of advantage and challenges for the flexible riser can be summarized on the table below,

3.       Hybrid Riser

Hybrid riser design in principle is combining both steel material risers and flexible riser material. A hybrid riser system typically consists of near-vertical steel pipe connects the subsea wells to the floating production unit (FPSO), near-surface buoyancy tank provides upward force to tension the steel riser and flexible pipe connects the steel riser to the FPSO. The combination of these elements allows hybrid risers to leverage the advantages of both steel and flexible riser where flexible jumper absorbs dynamic loads, while the steel riser provides structural integrity.

The list of advantage and challenges for the Hybrid riser can be summarized on the table below,

Selecting the right riser concept for an FPSO project remains a critical decision. As the industry continues to explore deeper waters and more challenging environments, engineers and project managers must weigh the advantages and disadvantages of each riser type. Whether it’s the adaptability of flexible risers, the robustness of SCRs, or the versatility of hybrid risers, the goal remains the same: safe and efficient hydrocarbon production. By considering water depth, environmental conditions, vessel dynamics, and cost implications, we can make informed choices that enhance project success. As we move toward a sustainable energy future, the evolution of riser technology will play a pivotal role in unlocking offshore resources while minimizing environmental impact. Let us continue to innovate, collaborate, and optimize riser designs for the benefit of our industry.