LDD was called upon by McDermott to provide custom-made under-reaming technology for large diameter drill bits to enable formation of 'ribbed' rock socket foundations for the Pluto Jacket installation, offshore Australia.
McDermott required our in-house engineering team to come up with a specialist rock socket solution. To meet client requirements, the design had to ensure the piled foundations of the Pluto Jacket attained enough tensile capacity to resist against all expected environmental loading on the structure.
Utilising all of our understanding and expertise in drilled foundations, LDD combined resources to evaluate client requirements and develop the most effective solution for the project. It was decided that to achieve these pile capacities, approximately twelve girth grooves/teeth would be created in each of the twelve drilled foundation pile sockets. Following design, fabrication and supply of the custom-made drill bits, the grooves were successfully drilled at 1.5m vertical intervals over a distance of 18.5m in a water depth of 115m. LDD operations were considered a real success; highlighting our reliability for engineering, procurement and supply services for large scale drilling operations.
“We are very pleased with the experience applied to the design of the Borehole Roughening Tools and congratulate your (LDD) design team for a first class design which has proved 100% reliable for the whole drilling campaign” – Pluto LNG Development (Woodside Burrup Pty Ltd) Woodside Energy Ltd, Australia
Jacket foundation design requiring a custom-made LDD EPC solution
The Pluto gas field was discovered in April 2005 in the Carnarvon Basin of West Australia and is located approximately 190 km North West of Karratha on the Burrup peninsula. It is situated in water depths ranging from 300m to 1000m and will initially be developed through five subsea wells in approximately 850m of water. The Pluto riser platform that LDD helped to install is located in approximately 83.5m water depth.
The Pluto Jacket is configured as a launched four-leg extended base tower with twelve piles (3 per corner) installed vertically in corner pile sleeves. The piles have a target penetration of 30m below mudline. Pile installation was facilitated by two installation work decks installed on the top of the jacket for the duration of piling operations.
The Pluto Substructure is founded on twelve 3m diameter drilled and grouted piles, each relying on a “roughened” borehole for load transfer to the surrounding formation.
LDD designed and built the under-reamer to act as a ‘Borehole Roughening Tool’ and be utilised in conjunction with the PBA913 reverse circulation drilling spread to provide the girth grooves in each of the drilled foundation pile sockets.
With years of engineering experience in foundation engineering, The LDD Engineering team swiftly designed and delivered the 3220mm under-reamers which were shipped to the mobilisation site in Batam Island off Singapore.
To minimise operational costs of the expensive semi-submersible jacket installation vessel during the drilling operations, the complete drill string was installed within the conductor pile at the Batam Island mob site. An LDD senior driller attended the drill string assembly and mobilised the under-reaming units.
Following installation of the jacket and the conductor pile at its first location, the client drilled to the depth where the first girth was required and the LDD team started the under-reaming operations. Wherever the team was not under-reaming, LDD provided the client with support on drilling and other installation operations.
The client achieved great value for money, not just for LDD’s under-reaming solution, but also for its assistance during other operations, making the most of our team’s wealth of experience in offshore foundation contracting.