Planning of a marine operation with focus on discussing limiting wave conditions

Abstract

The planning of a specific marine operation done by Ocean Installer is carried out in this thesis with regards to weather conditions on the Norwegian Continental Shelf. This is done by looking into the wave statistics from hindcast data at four different locations close to Ekofisk, Statfjord, Heidrun and Snøhvit. Metocean data is established for all fields for the purpose of understanding the impact from wind waves and swells, summer and winter, at the different locations. The author has developed a script in the mathematical software MATLAB for simulating the operation with various criteria. The output from the script gives the mean, P-10, P-50 and P-90 durations, with the assumption that the operation starts waiting for weather the 1st each month. The simulations are based on weather criteria provided by Ocean Installer and vessel motions calculated from probability models. The weather criteria provided by Ocean Installer is used to simulate the basis operation durations, and assuming vessel motion limitations. The basis simulated operation duration is further referred to as the weather criteria simulation. The weather criteria simulation is done by using total sea from one direction. These simulated operation durations are compared to simulations using vessel motion limitation. The vessel motions are calculated with impact from both wind waves and swells from different directions using RAOs for the vessel Normand Vision provided by Ocean Installer. The simulated operation durations show how the impact from waves with two different directions (wind waves and swells) vary from the same vessel motion criteria with waves from one direction (weather criteria simulation). The results from the simulated operation durations shows that limiting the whole operation to heave motion gives far longer duration than seen from the weather criteria simulation. Limiting the vessel roll motion gives more comparable durations to the weather criteria simulation, which is also the basis for Ocean Installers weather criteria. The Ekofisk field is operable almost all year long. Statfjord and Heidrun are very similar and are operable in the summer months of May to August. Snøhvit has the same operable months as Statfjord and Heidrun but less risk of waiting for weather during the rest of the year.