Understanding client requirements and applying its in-house engineering and project capabilities, LDD deployed a custom-made solution for a jacket installation project in the Ebouri Field, offshore Gabon.
Due to previous successes, the LDD team were brought in by VAALCO Energy to execute the pile installation work for an oil and gas jacket, 40km off the West coast of Africa.
Our scope of work included drilling and grouting of 4 No. through-leg 42″ tubular piles in 81m of water. Working directly on the project’s critical path, with a client vessel that had a significant day-rate, our team’s performance and contingency measures had to be first class.
With competant mudstone and sandstone bedrock expected at a very remote site location, the LDD project team had to be prepared for drilling in all conditions. With this in mind, the team prepared drill bits for all geological conditions likely to be encountered and an extensive inventory of spares in the unlikely event of a breakdown.
Specialist down-hole equipment was provided as contingency to cover any equipment failure. Additionally, a spot grouting and under-reaming programme was developed to stabilise the ground if the mudstone was found to be too weak.
The project demonstrated LDD’s ability to provide an efficient service, critical to the path of the project, whilst mobilising highly technical and bespoke equipment to a remote offshore location, ready for use in all eventualities. The project was successfully performed on time and without incident. The equipment coped perfectly with a variety of soils and rock, and the lift compensator exceeded all expectations offering tremendous control and time savings.
“LDD’s service added values, and if I ever have to drill and grout piles again, I would not hesitate to call them. They know their business; they bring certified qualified people; they have the equipment; and they are easy to get along with and are knowledgeable. To me, it is refreshing to pay someone to do a job and have them just go out and do it” Joe Delahoussaye, Construction Project Manager, VAALCO.
No of piles: 4
Pile diameter: 42″/1066mm
Pile length: 123m (transported in 3 sections)
Water depth: 81m
Socket depth: 34m
Geology: Unconsolidated clay, mudstone, sandstone and siltstone layers
The first challenge was working from a floating construction vessel (Global Industries’ heavy lift barge, the DP Hercules) onto a fixed platform on the seabed and dealing with the vessel heave motions and forces. The solution – a passive heave compensator with a 3m stroke for safe working loads up to 60t to negate the potential point loading and snagging impact. Using this innovative device, the point loading was reduced to just under a tonne.
This was the first known drilling and piling operation that had used a lift compensator at the time. As a summary of the success of this technology, LDD successfully mitigated against several instances where the project would have normally suffered weather-related downtime without the heave compensator.
A special in-drill-string hydraulic power pack and actuating equipment were developed for working down-hole, as well as a 42″ gripper can featuring a remote, pneumatic, gripping connection capable of withstanding the dynamic and passive forces that the drill generates. Heave was likely to be an issue and therefore the gripper can was specifically designed for drill rig lifting in marine environments.
The LD612 drilling rig was specially reconfigured for offshore use to enable drill-string running. This had a maximum drill diameter of 2.0m and featured 88,000 ft/lb (119kNm) of torque, a maximum thrust of 55t and a pullback of 65t. The inherent design of the drill bit was such that it would avoid the cutters getting stuck out of the casing when extended by the under-reamer. This is an uncommon but serious problem during drilling operations, which is mitigated by correct under-reamer design and operation experience.
LDD also designed and manufactured the drill bits needed for the varying ground conditions, including two 36″ drill bits with a 48″ under-reaming capability that enabled the drill bit to expand beneath the toe of the pile.
The soil conditions encountered were more problematic than expected, with a high degree of clay in places some of which was unconsolidated, inter-banded with mudstone, siltstone and sandstone layers.
Upon completion of the 34m socket, prior to the removal of the drill bit and bottom-hole assembly, the unconsolidated clays were supported with a proprietary shaft stabilizing mud product which increased the socket stand-up time for safe pile insertion and grouting.
LDD provided specialist pressure grouting equipment and supplied 282 t of grout procured and mobilised from Europe to ensure quality of supply. This was used to grout the piles into the rock socket.