Efficient Anchoring System for FPSO in Arbitrary Waters

Oil offshore Brazil, as well as in other continents, has demanded floating units for oil production. Typical anchored production units are the semi-submersible platforms, FPSO, Spar Buoys and TLPs. All of them use several anchoring lines for station keeping. In the offshore Brazil scenario, the last twelve years the FPSOs adopts the torpedo piles and polyester ropes in the anchoring lines in deep and ultra-deep waters. The FPSO “Cidade de Angra dos Reis” was the first to operate in pre-salt area in October 2010. From then on, it became common the production units with VLCC size, oil production of 150,000 barrels per day and 24 anchoring lines. The reason for such large number of anchors is the 1,200 tonnes torpedo piles holding power restriction. The proposition developed in this paper reduces the number of anchor lines using well know offshore equipment such as: driven piles, mooring chains, polyester ropes and conventional anchoring deck equipment. The main difference is the use of driven piles with holding power above 1,800 tonnes and anchor lines with a breaking strength of more than 2,000 tonnes. It is shown that a decrease of number of anchoring lines from 24 to 12 can be achieved. Consequently, it will decrease also the space occupied by the anchoring lines in the seabed by reducing the subsea layout of risers, flow lines and well head. This allows a technical and economical scenario more feasible when compared with the currently used on the Brazilian oil & gas market.