Online riser monitoring system for Skarv FPSO

Abstract

Customized production and storage vessels, known as FPSO (Floating Production, Storage & Offloading vessel), are increasingly used in offshore oil and gas production due to their flexibility and ability to produce in deep water while exposed to severe weather conditions. With help from a dynamic positioning system and mooring system, the vessels can more or less keep their position through harsh storms. However, the vessels will have considerably larger movement than a rigidly fixed oil platform. One of many challenges is to avoid environmental loads being transferred to vulnerable equipment. Even smaller positioning offsets can cause serious consequences to the risers. On most FPSOs, bend stiffeners are used to reduce bending forces at the interference point where the risers protrude from the turret on the way down to the seabed. The bend stiffener has a potential to fail and cause serious damage to the riser as they experience large bending forces in unfavorable weather conditions. This study has its background from industry incidents where the bend stiffener has loosened without any real time knowledge of the failure. Thus, the purpose of this thesis has been to evaluate the possibility of an online monitoring device to provide a real time image of the riser positions. By doing so, the riser movement pattern can be recorded. Consequently, if an abnormal movement is recorded, the bend stiffener has most likely failed. The main focus for this master thesis was to come up with the design of a deployment system to meet the given requirements of providing an online riser monitoring solution for BP’s Skarv FPSO. The thesis will evaluate different design alternatives and investigate the environmental loads the system will experience. Structural response and capacity analysis will be carried out for the important components to make sure the deployment system is suitable for further development.