Project Overview
Offshore facilities to gather and partially process gas and associated condensate and deliver it onshore for further processing. Key offshore components include:
- Well infrastructure and subsea installations
- Gas processing platform in 73m of water
- 225km trunkline to transport gas from the platform to the onshore facilities at Ashburton North.
The platform J-Tubes were at risk of sagging fatigue due to the high water velocities at the base of the structure. Technip approached MMA to design a formwork that not only supported the J-Tube but also shielded it from the lateral flow.
MMA's Solution
Subcon’s scope was to design and supply a support solution that would protect the J-Tubes from sagging fatigue, complete with a high shoulder to shield J-Tube from high flow velocities. We designed it with heavy density grout to ensure it will remain stable in cyclonic conditions. The deliverables included:
- 12 bespoke fabric formworks
- 3rd party validated grout design
- Full-scale onshore System Integration Testing (SIT)
- Additional custom grout supports with scour skirts for flowline free spans
Outcome
We developed a full-scale SIT for proof of concept before mobilising the solution. We then customdesigned installation housing suitable for a oneyear design life to allow for the deployment of J-Tube supports on a separate campaign, and off the critical path.
The design of high-density grouted support was significantly cheaper than competing solutions (steel support), helping our client keep within budget while providing a hard-wearing solution. The solution also had a custom scour protection design for the flowline supports to ensure longevity.
Technical Details
- Density – 3.6 Te/m3
- Formwork volume – 25m3
- Grout designed for workability – 200m horizontal pumping distance
Key Equipment
- Custom-designed fabric formworks
- Neutrally buoyant deployment frame suitable for ROV handling
- MMA’s Twin Pan Mixer for heavy density grout mixing and pumping
MMA Innovation / Value Added
Post-installation monitoring after cyclonic conditions showed no movement of grouted supports with constant connection with J-Tubes and no scour has been observed around flowline supports to date.