Design for Deepwater Pipelines on Steep Slopes Impacted by Mass Gravity and Turbidity Current Flows

摘要

Deepwater pipelines and flowlines that are routed across areas of steep slopes have the potential for seabed instability. They are at risk of being impacted by geohazards in the form of mass gravity flows (e.g. mud flows, debris flows etc.) and turbidity current flows. This paper discusses the impact of accidental environmental/geohazard loads on oil and gas pipelines routed across an area of seabed with a steep slope. The vertical gradient along the route ranges between 5° and 15° with a maximum local gradient in excess of 36°. The main design issues that needed to be resolved were the pipelines' global stability while resting on the steep seabed slope and their capacity to resist environmental loads (geohazards). Due to the nature of the problem that encompasses several unknown factors, conventional pipeline/flowline engineering was not sufficient to adequately define the response of the overall system. To address this issue, a series of fit-for-purpose full 3-Dimensional finite element models were completed to assess the global stability of the system and subsequently assess the impact of geohazard loads. With the help of extensive 3D finite element modeling, the impact of geohazard loads on the pipelines was assessed and the feasibility of the system was qualified through application of Accidental Limit State (ALS) design.