Wellhead platform subjected to accidental loads
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- Institutt for marin teknikk 
Cost reduction in the oil and gas industry forces new and innovative solutions.Unmanned wellhead platforms are alternative solutions for developing small fieldswhich would normally be developed with subsea wellheads. For an installation tobe approved to operate on the Norwegian Continental Shelf, it must be designedagainst accidental actions such as fire.Current rules regarding design against fire loads has been reviewed, showing examplesof heat transfer hand calculations, as well as material's strength degradation asfunction of temperature.A generic wellhead platform has been designed, based on comparable structures, andsimple hand calculations to have a reasonable model to work with. Conservativenesshas been applied to end up with a tough structure and reduce the need for passivefire protection. The structure was tested against normal operational loads and wereproven to have more than sufficient resistance.Operational-, variable maintenance- and accidental loads has been established withhelp from Trond Granli in Kværner. Characteristic fire scenarios were provided andcases set up.A shell script has been adapted for use on the heat transfer and response simulations.Trouble with multi- threading simulations prevented it from functioning perfectly,but it worked for single- threading.A large amount of simulations has been run, resulting in the conclusion that loadsrelating to wireline well intervention operations in combination with moderate jetfires is survived by the structure. Reserve strength ratios in the range above 4.5 wereexhibited. The case of accidental jack- up rig cantilever collapse was shown to betolerated, and the case involving a large jet fire inside the platform also survived theduration of the characteristic fire scenario. But further simulations are recommendedto confirm. Temperature- domain simulations has been run to validate a few of thepushdown simulations, with promising results.A good pool fire model was not established, but was simulated with the standardhydrocarbon temperature curve. The results showed adequately strength after theduration of the fire.