Riser-Soil-Fluid Interactions for Steel Catenary Risers

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Steel catenary risers (SCRs), comprised of thick-walled steel pipes and attached in a catenary shape from a floating system to the seabed, are widely used in offshore oil and gas field developments. SCRs must have sufficient strength to sustain significant fatigue loads caused by harsh ocean environments and the riser operational loads. Accurate prediction of the SCR fatigue life in the touchdown area, where the catenary riser departs from the seabed towards the floating system, is one of the most challenging design issues. There are several complex interactive mechanisms between the three main domains, i.e., riser, soil, and seawater. This leads to deep penetration of the SCR into the seabed and a significant influence on the fatigue life. Advanced riser-seabed interaction models have been developed in recent years to simulate riser penetration into the seabed and its influence on riser fatigue. However, previous models have typically only considered two domains of interaction, i.e., the soil and the riser. The detailed influence of seawater around the riser as the third domain has often been neglected. In addition, past models generally suffer from shortcomings and inconsistencies in the explicit modeling of the trench and premature stabilization of the embedment. Recent studies have strived to develop more accurate and comprehensive models to better predict the mechanisms contributing to trench formation, such as plastic soil deformation due to cyclic riser-soil interaction, and soil erosion due to combined vortices generated by subsea currents, cyclic riser oscillations, and riser-fluid interactions. In this research program, a new riser-soil-fluid interaction model will be developed to address the shortcomings of existing riser-soil interaction models and incorporate the effects of seawater in riser-seabed interactions, trench formation, and consequently the SCR fatigue performance. The numerical models will be validated against past published data and applied to a global SCR system to predict the ultimate trench geometry under a range of environmental and operational loads. Also, a new methodology will be developed for incorporation of the trench effects into the SCR fatigue analysis. This research program aims to improve the safety, integrity, and cost effectiveness of SCRs in the development of offshore fields. Considering the offshore field developments in Newfoundland and worldwide, this research has significant potential economic benefits both locally in Newfoundland and globally. Also, highly qualified personnel will be trained in a multidisciplinary environment while gaining valuable skills in the development of advanced engineering models, simulation tools, and methodologies.