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An investigation into the formation, shape and stiffness of seabed trenches around pipelines, risers and chains
This research project investigates the formation of trenches around objects on the seabed, such as pipeline, risers and mooring line chains, and the consequences of these trenches on the object-soil interaction forces at the seabed.
The preliminary portion of the project investigates the theoretical drained resistance provided by the seabed against object penetration or breakout. The second portion investigates the formation and development of seabed trenches due to oscillation of objects near or in the seabed. Finally, the results of the first two parts of this project will be used to develop a new object-seabed interaction model explicitly incorporating seabed trench formation and development into the overall response.
This research will focus on answering three key questions:
i) When and how will trenching occur beneath oscillating objects at or in the seabed?
ii) What limiting trench depths and geometry will be reached?
iii) What will be the seabed reaction to the object during trench formation and at the trench limiting condition?
Risers, pipelines and mooring chains are essential elements of the infrastructure used to develop offshore oil and gas resources. Interaction of these infrastructure with the seabed can lead to significant trenches around the infrastructure, the formation of which is poorly understood at present. There are significant opportunities for improved engineering design and reduced risk if this trenching behaviour can be successfully modeled.
Current consequences of seabed trenching uncertainty include:
i) Limitations on the applicability of steel catenary risers due to uncertainty in seabed condition.
ii) Massive risk associated with semi-taut mooring systems worldwide due to mooring line trenching.
iii) Underestimation of the benefits of seabed mobility and trench evolution near pipeline free spans, which may limit unnecessary and costly remediation.