Well fatigue assessment is an important aspect of the design and integrity assurance of deepwater riser-well systems. Fatigue damage arises from stress changes in a conductor due to cyclic loading. In practice, the lateral cyclic soil response is typically modeled using Winkler type springs known as the soil resistance-displacement (p-y) springs. An appropriate soil model for conductor-soil interaction analysis should predict the absolute and incremental magnitudes of stresses and the resulting impact on fatigue. Monotonic p-y relationships (backbone curves) which were originally developed for piled foundations are not appropriate for well conductor fatigue analysis. To determine the appropriate soil response an extensive study involving physical model testing in a geotechnical centrifuge and numerical analyses was initiated. The intent was to develop a robust and comprehensive approach to cover a wide range of seabed soils and loading conditions specifically for conductor fatigue analysis. Soil p-y models were developed for conductors installed in normally consolidated to lightly overconsolidated clays, medium-dense sands and over-consolidated clays. The models rely on the cyclic response of degraded soil at the steady-state condition and provide fatigue life predictions with high accuracy. This paper provides an overview of the past and recent studies that led to development of the fatigue p-y models. It presents the results of two centrifuge test series conducted in normally consolidated clay and medium dense sand. Ultimately, the paper provides recommendations for developing p-y springs specifically for well conductor fatigue analysis.
Buried pipeline heat transfer modeling has become an important topic in the Oil and Gas industry. The viscosity of fluid i.e. crude oil travelling through the buried pipeline largely depends on the flow temperature and pressure. The aim of this paper is to give an overview of designing the experiment for heat loss from offshore buried pipelines and validation of the experimental model using analytical solution and CFD modeling.
Several benchmark tests have been performed to ensure the validity of the test using theoretical shape factor models which depend on the amount of heat flow, thermal conductivity and geometry of the surrounding medium. This theoretical model has limitations such as the assumption of uniform soil properties around the buried pipeline, isothermal outer surface of the buried pipeline and soil surface. This paper illustrates several steady state and transient experiments to simulate the mechanism of heat loss from an offshore buried pipeline along with the experimental procedures. This paper also shows the transient response for shutdown tests performed in dry sand medium with numerical runs as well. With the progress of the research, several investigations will be made using different burial depths and diameters of the buried pipeline with backfill materials and trenching for different soil conditions, affecting the actual behavior of the model.
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