Geohazard Study of Mudslide Event at a Subsea Escarpment and Structural Response of Crossing Flowlines: Part I – FEA Analysis

Subsea earthquakes have the potential to cause mudslides on the seafloor. These extreme events can have a significant impact on the structural integrity of subsea flowlines and umbilicals. A numerical geohazard study is performed on a subsea mudslide event occurring at an escarpment. The study objective is to determine the structural response of flexible lines crossing the escarpment area when subjected to an extreme mudslide event and to determine both the survivability of the lines and the need for proposed anchoring devices. The study utilizes several numerical methodologies of increased complexity, precision, and cost, such as Finite-Element-Analysis (FEA), Computational-Fluid-Dynamics (CFD), and Fluid-Structure-Interaction (FSI). This paper focuses on the FEA analysis, with the CFD and FSI analyses presented in a separate paper [1]. The FEA methodology reduces conservatism over conventional approaches by applying the mud debris flow effects on the flexible lines with a one-way CFD to FEA coupling and a morphing escarpment bathymetry. A CFD simulation is performed on a rigid seabed bathymetry to extract the mudslide velocity field at every second. This velocity field is applied to the Abaqus FEA simulation using Abaqus/Aqua with a one-way coupling approach, thereby allowing the FEA model loading on the flexible flowlines to be updated from the load created by the mudslide motion. A key finding from the FEA study is that although the mudslide event creates large displacements in the flexible lines, it does not significantly pull the flexible flowlines over the escarpment, thereby eliminating the need for planned anchors and saving significant capital expenditure and installation costs.