Study of the module handling system on Seven Viking

Abstract

Subsea installations is a vital part of the oil and gas industry, but as have also been a major cost factor. When the oil price decline, subsea installations are one of the first fields to be affected. The priority to cost optimize have never beenmore important. Using module-based subsea installations allows for simplified maintenance and fast replacement, thus minimizing downtime. Subsea modules allows for easier installations compared to fully integrated subsea equipment as the modules are smaller and lighter. This allows for a wider range of construction vessels to be considered for installation. Light construction, intervention and Inspection,Maintenance and Repair (IMR) vessel may all be considered for installations of subsea modules. A normal feature of these vessels is the use of a Module Handling System(MHS). The MHS is a system that allows for a safe and predictable deployment and recovery of modules. Subsea modules can be of such a size that the capacity of the vessel is challenged. In this thesis a study of the MHS has been completed. Themain part of the study has been to use Simulation ofMarine Operations (SIMO) to simulate and analyse the critical phase where a module is suspended in air from the MHS tower. A literature study presenting the previous work done by Subsea 7 where the critical aspects of deployment and recovery through moonpool is presented and discussed. The analysis show that resonance between vessel motion andmodule motion is a major issue when the module is suspended in air. This cause limitation in operability. Analysis show that the operative sea state can increase if the design of guidance systemon the MHS is modified. The sea state can be further increased by adding means to equalize the resonance. Previous work done by Subsea 7 show that clearance between the modules and the moonpool walls are critical formodules that is in the vicinity of the capacity limit of theMHS. Based on the results from the analysis presented in this thesis and from previous work by Subsea 7, the technical requirements stated by Statoil in TR1231 for MHS seem unrealistic and are unlikely to be met.