For pipe lay operations parameters like heading and position of the lay vessel, lay-back and information about feeding of joints are usually collected and stored by the contractor. Many lay vessels are also equipped with a MRU unit for measurements of dynamic vessel motions, and in some cases the current profile is also monitored. This is especially the case for pipes with low bending stiffness and low ratio between weight and drag diameter (i.e. small pipe diameter) where current is important for the configuration of the pipe catenary. Together with the seabed these parameters constitutes the boundary conditions for a nonlinear time domain analysis of the lay operation. Such an analysis approach will have a wide range of application areas, from online monitoring to realistic back-calculation of a lay operation. During recent year’s work with the Ormen Lange field (see Figure 1) Marintek has developed a new generation of 3D pipeline analysis tools. Ormen Lange is the largest natural gas field on the Norwegian continental shelf. The field is situated 120 km northwest of Kristiansund. The seabed depths in the reservoir area vary between 800–1100m, and the terrain is very rough due to remnants from the Storegga slide. In the period 2006–2007 two 30" import lines, two MEG lines, and two umbilicals were installed at the Ormen Lange field. In the present paper monitored data collected during the installation of the 30" pipelines are used to back-calculate the lay operation. The agreement between observed and calculated lay parameters are reported and discussed.

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