Application of Flexible Risers in Shallow Water: Weight Added Wave Configuration

Abstract

Unbonded flexible pipe has been a proven technology for riser solutions in offshore oil and gas production since the 1970s with over 2000 risers installed. The operating envelope for flexible riser configurations has continually expanded to meet the challenges of both shallow and deep water applications [1]. This paper presents recent innovations in technology for flexible riser solutions to enable oil and gas development in water depths as low as 20m with required system reliability as well as cost effectiveness. For shallow water applications, the traditional technology is the wave or S configuration. S configurations require a structure such as a mid-water buoyancy arch (MWA) to support the riser configuration, which increases the cost of both fabrication and installation. The wave configuration with distributed buoyancy is a more cost-effective approach in terms of installation. The disadvantage of this solution is that the riser could either float to the water surface or sink to the seabed when its content density varies or the floating production, storage and offloading vessel (FPSO) deviates from its nominal mooring position during field production. A new modified wave configuration, referred to as the Weight Added Wave (WAW) configuration (Patent pending) is presented, which enjoys the low installation cost of the wave configuration and performance reliability of the S riser configuration. The WAW configuration has been applied to two FPSO shallow water field developments and the results are presented herein to confirm the solution for real life applications.

Review of the Development of an Unbonded Flexible Riser: New Material, Types of Layers, and Cross-Sectional Mechanical Properties

“…The configurations evolve from the catenary to include the following: the lazy wave configuration, which offers a more relaxed curvature; the steep wave configuration, characterized by sharper bends; the lazy-S configuration, which introduces an S-shaped pattern with a gradual transition; the steep-S configuration, featuring a more pronounced Sshape with abrupt changes in direction; the pliant wave configuration, which provides flexibility to adapt to various marine conditions. Each of these configuration designs is tailored to different requirements, ensuring that dynamic risers can function effectively in diverse marine environments [30]. A typical configuration of an unbonded flexible riser with composite tensile armor layers is shown in Figure 12, wherein the top riser is the unbonded flexible riser containing the composite material tensile armor layer, and the bottom riser is the conventional unbonded flexible riser containing steel tensile armor layers.…”

“…The configurations evolve from the catenary to include the following: the lazy wave configuration, which offers a more relaxed curvature; the steep wave configuration, characterized by sharper bends; the lazy-S configuration, which introduces an S-shaped pattern with a gradual transition; the steep-S configuration, featuring a more pronounced S-shape with abrupt changes in direction; the pliant wave configuration, which provides flexibility to adapt to various marine conditions. Each of these configuration designs is tailored to different requirements, ensuring that dynamic risers can function effectively in diverse marine environments [ 30 ].…”