Introducing a Novel Shaped Steel Catenary Riser for Deepwater Applications

Abstract

Abstract Use of steel catenary and lazy wave risers has increased as oil and gas developments are happening in deeper waters or in parts of the world with no pipeline infrastructure utilizing Floating Production Storage and Offloading (FPSO) vessels as a host platform. A suitable Catenary form is selected based on the hang-off angle of the riser. Lazy-Wave form of the catenary riser is achieved by targeted placement of a custom configured buoyancy section. This includes the length to start of the buoyancy section, length of the buoyancy section, hang-off angle, and the buoyancy factor. The strength and fatigue performance of steel catenary and lazy wave risers are governed by its configuration parameters. Achieving these key performance drivers for an SCR or SLWR takes several rigorous analyses iterations throughout the design process. However, on many occasions a modified and optimized Shaped Steel Catenary Riser (SSCR) is necessary to satisfy the project technical, operational, and economic requirements. In certain instances, there is simply no solution achievable using a monolithic steel catenary or lazy wave riser. These include instances where an SCR may be technically feasible, however the top tension is too high or an SLWR simply doesn't have adequate operational fatigue. A shaped Steel-Titanium Riser (STIM Riser) allows to decouple the vessel motions sufficiently and reduces the hang-off tensions. The concept also provides good long-term and short-term fatigue due to environmental factors including wave and currents and operational factors such as slugging. In this paper a novel hybrid shaped riser is introduced. This riser system takes advantage of the modified catenary riser to achieve an optimized shaped SCR and combines it with the superior fatigue performance of Titanium. Titanium is abundant in the nature but currently difficult and expensive to extract at large scale. The industrial solution to produce Titanium at a greater scale is expected to improve in the near future. In that scenario, a riser system with Titanium applied to several critical areas will provide an attractive solution. This customized solution provides an attractive cost optimized configuration that meets all requirements.