In the last decade, mooring systems have been selected for the production units and mobile drilling rigs required to operate between about 300 and 3000m of water. The paper emphasizes on the empirical evaluation and installation behavior of suction piles and plate anchors, which currently appear as the two main anchor solutions in soft deepwater clays. Regarding the vertically loaded plate anchor (VLA) solution, several VLA concepts are in competition, including the ‘Stevmanta’ and ‘Dennla’ drag-in plate anchors, and the direct embedment ‘SEPLA’ anchor installed by means of a suction follower. From the current experience with deepwater moorings, general trends are suggested with respect to the design of plate anchors in soft clays.
In about a decade, reliable and cost effective mooring systems have been selected for the floating production units (FPUs and FPSOs or FSOs) and mobile drilling rigs (MODUs) required to operate between about 300 and 3000 metres of water. Improvement in the stationkeeping area of oil production floaters in deep waters included both the mooring lines and anchors, in particular with the use of anchors with a vertical loading capacity and fibre ropes in taut leg mooring (TLM) configurations (Colliat, 2002; Ehlers-Young and Chen, 2004).
In front of the conventional driven pile solution, now applicable in up to about 2000 metres of water (present limitation of underwater hammers), the paper emphasizes on the empirical evaluation of suction piles and plate anchors, which currently appear as the two main anchor solutions in soft deepwater clays. In the Gulf of Mexico and in West Africa, the suction pile is the preferred option for permanent mooring of production units, including semi-submersible FPUs and deep draught SPARs in the Gulf of Mexico, or FPSOs in the Gulf of Guinea.
