Riser Cutting and FPSO Disconnection
Project
Riser Cutting and FPSO Disconnection
Location
North Sea
Water Depth
90m
Project Type
Decommissioning
Project at a glance
Subsea 7 delivered an ROV deployable cutting solution to disconnect 5 risers and moorings from an FPSO.
Barracuda connectors fitted to the risers meant each transition piece was different geometry. All locations were to be cut as close to the hull underside as possible and the diamond wire saw (DWS) would need to be flown by ROV to all 5 locations.
Highlights
The project yielded a number of successes including:
- Designed and fabricated a bespoke engineered riser cutting solution
- Utilising our existing DWS fleet
- Overcame a challenging decommissioning problem for our Client
- Mitigated diver risk
- Solution available for other projects
Solution
Subsea 7 developed a bespoke engineered solution utilising our existing DWS fleet to fulfil the following requirements:
- 48” ROV DWS to cut transition sections containing risers and umbilicals as they enter the FPSO hull
- Modify deployment basket to allow 48” ROV DWS to be inverted and clamping arms to hold on above cut line of saw
- Develop subsea docking system to allow backpack orientation of DWS using hydraulic docking probes to connect subsea
- Full ROV solution to limit risk to divers and allow risers to fall to seabed once cut
- Concept trials and factory acceptance testing (FAT)
Scope of Work
FPSO riser and mooring disconnections were required as follows:
- 24” Gas Export disconnection cut
- 28” Production disconnection cut
- 24” Gas lift disconnection cut
- 28” Umbilical disconnection cut
- 24” Water injection disconnection cut
- Mooring lines disconnection cut
