Review of Steel Lazy Wave Riser Concepts for North Sea

Abstract

The Steel Catenary Riser (SCR) is considered a favorable solution for deepwater development. However, the application of SCRs in harsh environments is challenging, mainly due to fatigue at the touch down zone. One of the solutions to improve SCRs’ fatigue performance is the application of buoyancy modules in order to achieve a Steel Lazy Wave Riser (SLWR) configuration. This paper presents a parametric study of a SLWR system for application in deepwater and harsh environments. The selected harsh environment is the seas within the Norwegian Continental Shelf. The main geometric variations are the length of the buoyancy section and the dimension of the buoyancy modules. These variations result in riser configurations with different riser’s wave heights. The term ‘riser’s wave height’ refers to the vertical distance between the lowest point at sagbend and the highest point at hogbend of a riser. The analysis works are performed using Orcaflex. The results show that the application of buoyancy modules help to improve the performance of a steel catenary riser for application in a harsh environment. The dimension of a riser’s wave shape proves to be an important factor that controls strength and fatigue performance of a riser. Lazy wave riser configurations with larger and better defined wave shapes have lower stress utilizations and lower fatigue damage, while riser configurations with smaller wave shapes have higher stress utilizations and higher fatigue damage. This is due to lazy wave configurations with higher wave shape have better capability to absorb the dynamic loads.