On the feasibility of a novel concept for a free standing riser

Abstract

Free Standing Risers are well established in the oil and gas industry for offshore deepwater field developments. There are some challenges within the current system, however, in regards to the complexity of the rigid spool connecting the pipeline and the limitations to the flexible jumper connecting the production unit, which need to be carefully addressed in the design and in some cases may cause the system to be disregarded for specific projects.This work consists of evaluating the feasibility of a proposed novel system where the pipeline is integrated to the riser, considering a transition section to bring the lower catenary section to the near vertical section of the riser in a smooth manner by means of a multiple line system to keep the functionality and integrity of the entire riser along the full life cycle of the project. A steel jumper is also evaluated as a potential alternative to the traditional jumper made up of flexible pipe.The work applied the finite element analysis software dedicated to riser global analysis to assess the most promising configurations for the multiple line system and for the steel jumper, following analytical geometric models created to establish lengths and positions to be considered in the numerical simulations.As part of the work, it was developed a methodology for optimizing pipe wall to keep the buoyancy tank in reasonable dimensions. Static analysis was performed with the purpose of searching for feasible configurations for both systems, the multiple lines and the steel jumper, for a variety of production unit positions. Dynamic analysis was performed to assess capacity of the system to withstand extreme conditions. Finally, parametric analysis was performed to check the robustness of the proposed system to changes in the design nominal conditions, such as fluid density, pipeline end expansion, fabrication and assembly tolerances within the multiple lines, and installation tolerances for the suction pile.The results demonstrate potential utilization of the novel riser system applying a circumscriptive line model, which demonstrated working reasonably well in extreme conditions, having enough flexibility to absorb pipeline end expansion and fabrication and installation tolerances. The results also show potential application of the jumper to be made up of steel pipes applying stress titanium tapered joints at both ends for absorbing the movements of the production unit.