“Vertical type” spool configuration is commonly adopted as riser base spool for deepwater field development. With increasing water depths and risers subject to harsher environments, the excessive lower riser assembly motions and slugging induced fatigue damage have emerged as the governing design criteria for deepwater riser base spool design. Conventional vertical spool has inherent shortcomings to handle such design conditions. A new “hybrid” concept is therefore proposed, which extends beyond the “traditional” spool concept by integrating both vertical and horizontal spools into a 3D configuration. It inherits the vertical spool’s strength on handling large spatial expansion and utilise the pipe-soil interaction to dampen the potential resonance caused by slug flow.
Several prototypes have been examined and the hybrid spool expansion-mechanism is discussed together with an optimisation procedure proposed. An advanced FEA technique using both Abaqus/Flexcom has been employed as part of the hybrid spool development, which consists of rigorous 3D dynamic analysis, bespoke non-linear soil interaction model and utilising the global riser dynamic behaviour. An in-house spool automation tool is developed to optimise the iterative analyses required to obtain a satisfactory hybrid spool configuration. This paper described a successful case study in recent deepwater hybrid riser bundle (multibore hybrid riser) tower development project, where the need to accommodate large lower riser assembly motion and slugging fatigue damage are the two main design drivers. This presentation provides a creative insight into this innovative technology.