Layout Design Of Buoys In The Deepwater Lazy-Wave Riser System Based On Hydrodynamic Performance

Along with the advance of offshore reservoirs development,the exploitation of marine resources has gradually developed toward deeper water.Steel catenary risers are key components connecting the underwater production system with the platform on the surface of the sea.Because of the horrible environment conditions,they suffer enormous force and bending moment.As the improvement of steel catenary riser,steel lazy-wave riser with some buoys can effectively improve the force condition.It can resist a part of tension and reduce the load of the hang-off point,thus it will extend the fatigue life.This paper is making use of the numerical analysis and simulation to design the layout of buoys in lazy-wave riser system.This paper begins with a detailed introduction of steel lazy-wave riser and the buoy in the system.The governing equation which consider gravity and buoyancy is obtained based on the large deformation beam theory and the finite difference method and Matlab program is adopted to show the numerical results including the configuration of the lazy-wave riser and the mechanical performance along the riser.The space and the starting position of the buoys are taking as the design variables to study the influence of the layout parameters on the mechanical performance of the lazy-wave risers.The result show that the increase of the space can lead to a increase of the tension of the hang-off point but a decrease of the maximum value of the bent moment.Similarly,the increased distance between the starting position and hang-off point increase the maximum of the tension,while decrease the extreme bend moment.And then Orcaflex is used to prove this result.In addition,comprehensive analysis is carried out to investigate the influence of the different types of ocean current,such as uniform flow,shear flow and power-law flow.And in each situation,the layout parameters of the buoys are altered to compare the changes of the configuration and performances of the risers.Followed by these analysis,slug is considered.It is a transient multiphase-flow phenomenon that can occur in pipeline-riser system and affect adversely the equipment due to its large pressure and flow-rate fluctuations.Firstly,the difference between the simple pipe-line riser system and lazy-wave riser which consists of two inclined pipelines is studied,and then changes of the fluctuation period resulted from the different types of buoy layout are obtained,which can see the feasibility of the selected parameters in the first two chapters.According the result from the research,the final layout parameters of buoys are decided on the space 6-8m and the distance between the starting position and the hang-off point 1650-1700 m.This study is not only a beneficial trial to perfect the deepwater oilfield development system,but also an improvement to my ability of learning and applying knowledge.