Fully Coupled Time Domain Simulation Model Used for Planning and Offshore Decision Support During Riser Replacement Operations

This paper presents a dynamic analysis model where installation vessel in coupled with the riser system using the SIMA software. The model is used to assess risk and weather limitations for riser replacements performed with SIMOPRO (Simultaneous Marine Operation and Production). The SIMA model has been used in several complex riser replacement operations in the North Sea during 2017, and proven to be a vital support tool for decision making offshore. The analysis supported critical operational decisions that resulted in reduced weather downtime and enabled the marine operations to be completed in a safe and efficient manner, while the platforms were kept in production. In the planning phase the analysis model was used to test specific DP settings to minimize vessel footprint, optimize procedure steps and provide accurate limits to an Activity Specific Operating Guideline (ASOG). The model was further used to verify vessel and riser response subjected to various “emergency situations”, such as wire break and partial or full vessel black-out. The results were used to establish detailed contingency procedures. During the offshore operations, analyses were performed at regular intervals at the vessel with measured and forecasted weather data, to monitor vessel response and predict vessel drift-off trajectories in case of a vessel black-out scenario. The information provided by the DP recorder was fed back into the fully coupled analysis model where the Kongsberg Maritime DP settings were updated to reflect actual vessel system behaviour. The analysis model also provided vessel drift-off predictions in good agreement with real drift-off test results. With the optimized fully coupled analysis model it was then possible to perform simulations of the planned installation steps based on forecasted weather data.