Fugro Seacore Ltd (FSCL) was contracted by to install piles for a new jacket platform installation in the Avouma Field, located offshore Port Gentil in Gabon. The 4 legged structure had 90m long legs set on batters of 1 in 10 and 1 in 8. In a conventional jacket installation, piles would have been driven through the legs into the seabed, but at Avouma the holes for the piles had to be created first due to the bands of claystone and mudstone, with hardnesses ranging from 12 -70 mpa, extending downwards for tens of metres.
The pin piles were 42" OD, enabling them to pass through the 44" I.D. jacket legs. The 120m long piles were made up of 4 sections with a wall thickness 1" to 1.5i" and a total weight of 110t per complete pile. The first 3 sections were lowered into a jacket leg and welded together as they went in. This single length of about 100m protruded above the leg and was then dogged-off at the top of the leg to hold it steady. With the 4 piles dogged-off, FSCL’s specially modified 15t Wirth B5 pile top drill was lifted onto one pile and clamped into position. The unit’s hydraulic power swivel, capable of producing 5t-m of torque was driven by FSCL’s Volvo Hushpack hydraulic power units, via a 30m-long umbilical supply from Tidemar 240 support barge.