Dillon-Gibbons, C., Kilner, A.A., Thurumella, H., Carra, C., and Ryan, V., Paper Number OTC-31922-MS, Proceedings of Offshore Technology Conference, May 2nd - 5th, Houston, Texas, USA, 2022.


Disconnectable FPSOs are important systems employed by operators in regions that are subject to hurricanes and cyclones. A key to the successful disconnect of the mooring and riser systems is a robust evacuation procedure. To this end, this paper presents an evacuation procedure developed for an FPSO with a disconnectable internal turret mooring system. The advantage of the developed evacuation procedure is that by combining the forecast site wind and wave data, the analysis showed an increase in the number of times the facility could evacuate safely and, at the same time, provided increased uptime.
To test the evacuation procedure, an evacuation procedure modeling tool was developed that evaluated the procedure using historical hurricane/cyclone information such as the track position, forward speed, wind speed and wind radius, as well as 60 hour site wind and wave forecast data. Evaluated storms ranged from major cyclones to tropical storms that developed close to the offshore location of interest. The program performed evaluations from initial formation of the weather system through to the disconnect and sail away of the FPSO. An evacuation disconnect was deemed successful if all required evacuation procedures took place within the designated time constraints, as well as the disconnect operation occurring within wind and wave height limitations. Furthermore, the overall evacuation was considered successful if the FSPO was subsequently able to sail out of the hurricane path and not experience wind conditions of greater than 34 knots.

The tool was used to assess an example evacuation procedure for a disconnectable FPSO facility at 3 locations in the GOM and develop an understanding of the critical operations in the procedure and where optimizations could be made. Sensitivity analyses were conducted to understand the impact of changes in disconnect duration, vessel sailing speed, the disconnect and reconnect limits. Additionally, an assessment was conducted to understand the typical duration that the field would be shut-in when a disconnect was completed, and thereby understand how long it took for the FPSO to return to site and recommence normal operations.

Copyright 2022, Offshore Technology Conference

DOI: https://doi.org/10.4043/31922-MS