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Title: Pipeline/Riser soil interaction analysis
Keywords: steel catenary riser,clay,spring stiffness,touchdown zone,repeated loading,centrifuge modelling
Issue Date: 16-Aug-2010
Citation: HU HER JIA EDDIE (2010-08-16). Pipeline/Riser soil interaction analysis. ScholarBank@NUS Repository.
Abstract: As oil and gas production is moving towards deepwater regions, floating production system (FPS) such as semi-submersible, Floating Production Storage and Offloading vessel (FPSO) and SPAR are being utilized. The introduction of these compliant floating systems for offshore hydrocarbon production has led to the development of new designs for the riser pipes, with the steel catenary riser (SCR) often being the system of choice. Current riser-soil modeling practices are simplistic compared with testing and field observations, which reveal that the modeling of riser-soil interaction at the touchdown zone (TDZ) could be greatly improved. In the present study, centrifuge modeling technique was conducted to evaluate the soil responses when the seabed is subjected to repeated penetration and extraction. The present study concentrates on identifying the major factors that affect the riser-soil interaction. Load-displacement response, soil stiffness degradation and pore water pressure around the pipe were obtained from the centrifuge model tests. Both displacement and load controlled tests have been carried out. The effects of shear strength gradient, cyclic amplitude, water entrainment and cycling depth have been identified as the parameters that affect the riser-soil interaction. Particle image velocimetry coupled with close range photogrammetry technique were used to visualise the soil failure mechanism as the number of load cycles increases. Ring shear tests have also been performed on the clay soil in order to quantify the residual strength of clay at the steady state of cyclic motion. Based on the findings, upper bound solutions to predict the pipe penetration and uplift resistance were proposed and evaluated. These solutions are able to improve the prediction of penetration and uplift resistance at shallow embedment in clay with soil strength increasing with depth.
Appears in Collections:Ph.D Theses (Open)

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