Design and Installation of Suction Anchor Piles at a Soft Clay Site in the Gulf of Guinea

Innovative shallow suction anchor piles have been used for permanent mooring of a process and accomodation barge at an oil and gas field developed by ELF Congo in the Gulf of Guinea. The 12 mooring lines, equipped with 5m diameter and 13m high steel suction anchor piles, were successfully installed at the site in July/August 1995. The process barge is scheduled to be connected early 1996 for start of production. With a water depth of about 170m, the Nkossa field is the deepest in offshore Westem Africa to date. The soils at the site consist of soft normally consolidated clays, representative of deep water sites. The anchoring system design is presented, together with the description of the suction pile installation by underpressure. The monitored performance of the suction piles during installation is evaluated, including orientation and tilt at touch-down, and penetration rate during suction penetration. The installation behaviour appeared to be very smooth, and the measured penetration resistances were in perfect agreement with the predictions, thus demonstrating the reliability of the design installation method.