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

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.