StabFrame deployment for FPSO mooring anchor pile, Waimea, Campos Basin, offshore Brazil
LDD, an Acteon company providing near- and offshore specialist drilling and foundation installation services, successfully completed its first subsea pile installation campaign using its StabFrame subsea pile support frame.
Wellstream International Ltd carried out the recent pile installation operation, using the LDD StabFrame, offshore Brazil on the Waimea development in the Campos Basin on behalf of OGX Petroleo e Gas.
LDD provided pile stabilisation services for ten 84-in. diameter mooring piles that were driven in water depths up to 140m in preparation for installation of the OSX-1 Floating, Production, Storage and Offloading (FPSO) vessel mooring system. The StabFrame ensured that the piles were reliably stabilised while LDD’s sister company MENCK drove them to their respective targets.
Following completion of the offshore pile-driving operation, all equipment was rapidly demobilised. The modular design of the StabFrame makes it possible to transport it via conventional ISO freight containers, immediately freeing up the construction vessel.
CLIENT QUOTATION:
“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.
PROJECT STATISTICS:
SOW: FPSO pile mooring installation
No of piles: 10
Pile diameter: 84-in / 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
EQUIPMENT:
84” StabFrame
Pinned Lift Tools PLT
MHU500 Hydraulic Hammer
CHALLENGES:
Geology - pile stability without initial penetration and free-fall through unsupportive layers
Tidal currents up to 2.5 knots
Tight design, engineer and build programme of market leading StabFrame
PROJECT:
StabFrame’s maiden deployment was far from a straight-forward with challenging piling conditions due to the presence of a hard crust overlaying a very soft, unsupportive layer. This resulted in virtually no initial penetration followed by a free-fall situation as the crust was breached during driving. However, it was LDD’s unique design which proved far more versatile in coping with these conditions when compared with the standard industry approach.
The LDD StabFrame is custom-designed in keeping with DNV-OS-C20 guidelines. The design, fabrication and testing of the StabFrame was completed within a tight 8-week programme schedule ready to transport from the UK to Brazil on the offshore construction vessel Aker Wayfarer. Throughout, the initial design and build phase, LDD provided constant support to Wellstream’s engineering team to ensure that all aspects of the project were covered, particularly in terms of procedural documentation and stability analysis.
Upon arriving at Waimea field, LDD worked closely with the Wellstream team, providing guidance and support around-the-clock. Together, they 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 from the seabed, it was safely secured subsea on a hang-off post attached to the frame.
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. In spite of strong currents estimated at times to be more than 2.5 knots, work was carried out safely, well within the requisite timeframe and without a single lost-time incident.
ABOUT STABFRAME:
The StabFrame stabilises piling in water depths to 2000m, offering offshore construction companies a reliable, efficient and cost-effective way to ensure that every subsea pile-driving operation goes to plan. The StabFrame’s 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,” he added.
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 opening of a standard pile installation support frame relies on a release ring. It is welded to the pile at a point above which it has been pre-determined the pile will have achieved self-stability. This release ring triggers the mechanism to open the frame and allow the hammer to pass freely. However, if ground conditions are different from expected, the mechanism may release the pile support frame before stability has been achieved. This can lead to significant delays to the piling programme.
The StabFrame is operated via a work-class, remotely operated Vehicle (WROV) which therefore negates the requirement for an automated release system. Using WROV, allows the installation to be monitored and the StabFrame operator to react to 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’s. The system can be used for a wide variety of applications, including pre-installation of driven jacket piles, and construction of offshore wind farms and deep water anchoring projects.