LDD offered dedicated support and a custom-built solution for our client with the successful design, fabrication and delivery of our deepsea piling support frame; the StabFrame.
The LDD team custom designed, built and delivered the StabFrame to Wellstream International Ltd as part of a service for anchor pile installation on a Floating Production, Storage and Offloading (FPSO) vessel, offshore Brazil on the Waimea development.
As part of the project requirements, we implemented pile stabilisation services for ten 84” diameter mooring piles that were driven in water depths up to 140m in preparation for installation of the OSX-1 FPSO vessel mooring system. The StabFrame ensured that the anchor piles were reliably stabilised whilst our Acteon sister company, MENCK, drove the piles to the respective target depths.
Following completion of the offshore pile-driving operation, all equipment was rapidly demobilised. The modular design of the StabFrame made it possible to transport via conventional ISO freight containers, helping to immediately free-up the construction vessel.
“One thing that came out of the Waimea operation is the way that the StabFrame is able to adjust to unpredictable soil conditions.” said Frank Buck, Project Director – EPIC Projects for Wellstream International Limited. “Every pile went into free fall to varying degrees at varying drive depths, but the StabFrame allowed us to drive deeper prior to opening the frame, thereby guaranteeing stability. The StabFrame was deployed once and recovered once, remaining subsea for the duration of the 10 pile campaign.” he added.
No of piles: 10
Pile diameter: 84” / 2134mm
Water depths: up to 140m
Tidal currents: up to 2.5 knots
Geology: hard crust overlaying a very soft unsupportive layer
Average pile installation duration: <24hrs per pile
The deployment of the StabFrame offered the perfect solution to overcome the predicted challenging conditions due to the presence of a hard crust overlaying a very soft and loose sediment layers. The geology resulted in very little initial penetration of the piles followed by a free-fall situation as the crust was breached during driving. The unique design of the frame proved far more versatile in coping with the difficult geology compared with the standard industry approach, offering a great solution to overall stability and tolerance during driving operations.
The StabFrame was custom-designed in keeping with DNV-OS-C20 guidelines. The design, fabrication and testing was completed within a tight 8 week programme; ready to transport from the UK to Brazil on the offshore construction vessel Aker Wayfarer.
Throughout, the initial design and build phase, our ‘in-house’ engineering and design teams provided constant support to Wellstream’s project team to ensure that all aspects of the design and build were covered, particularly in terms of procedural documentation and stability analysis.
Upon arriving at the Waimea field, LDD personnel fully integrated with the Wellstream team, working closely to provide guidance and support around the clock. Working alongside the client, our team successfully situated the StabFrame at the first of 10 subsea pile-driving sites on the seabed.
Following completion of each pile-driving operation, the StabFrame was moved to the next site without returning to surface to reduce weather and sea state risk exposure. To eliminate the challenging prospect of recovering the StabFrame, it was safely secured to the subsea on a hang-off post attached to the frame during operations.
For 31 days, the StabFrame was continuously deployed subsea, performing as intended. All LDD-supplied equipment – including the WROV interface/docking station, hydraulic systems, pile-lifting and handling tools – performed well and ensured the project kept to the critical path. Despite strong currents estimated at times to be more than 2.5 knots, work was carried out safely, well within the requisite time-frame and without a single lost-time incident.
The StabFrame stabilises piling in water depths up to 2000m, offering offshore construction companies a reliable, efficient and cost-effective way to ensure that every subsea pile-driving operation goes to plan. Its ability to adjust to varying and shifting soil conditions on the seabed means that it effectively stabilises piles throughout the driving process.
“With the StabFrame, even if an unforeseen layer of soft sand is encountered, we can adapt to it.” said Steve Cuddihy, Project Design Engineer for LDD. “The StabFrame can remain closed and continue to stabilise the pile while it’s being driven further, saving time and money.”
Its modular design means that it is easy to transport, assemble and operate. Transport costs can be greatly reduced, in view of the fact that the system can be demobilised within 24 hours and shipped in conventional ISO containers, freeing up the construction vessel for use elsewhere.
The StabFrame is operated via a Work-class Remotely Operated Vehicle (WROV). This negates the requirement for an automated release system, as seen in standard pile support frames. Using WROV allows the installation to be monitored and the StabFrame operator can swiftly react to any variations in piling conditions.
Add-on modular features such as mud mat extensions and self-levelling systems further increases the adaptability and scope of the StabFrame. The system can be used for a wide variety of applications, including pre-installation of driven jacket piles, and construction of offshore wind farms or deep water anchoring projects.