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The paper discusses alternatives to represent the MLD (Mooring Line Damping) in models tests with truncated mooring lines. The work has performed both numerical experiments and reduced model tests. The results for stiffness and damping have been compared. This allows further considerations for future designs.

Offshore constructions costs can be very high when the operation requires the use of additional vessels and support tugs. This was the case in 2016, when some of the riser bellmouths needed to be replaced on one FPSO located offshore Brazil. The initial bellmouth change-out plan included an installation vessel plus support tugs to hold the turret moored FPSO in position. As a result of the current cost constraints in the offshore industry, it was necessary to challenge the conventional way of working and to re-evaluate the construction methodology. This paper presents the methodology used on the FPSO bellmouth change-out, where all operations were conducted from the FPSO, without the need for the installation vessel or support tugs. The FPSO for this case study is located in the Campos Basin deepwater, in 1485m water depth, and approximately 70 kilometers east of Victoria, Brazil. The FPSO started production at its current location in May 2010. The unit has a maximum oil production capacity of 100,000 bopd, and a gas processing capacity of 70 mmscfd. Oil is stored onboard and offloaded through a tandem moored shuttle tanker. The gas is compressed and exported from the FPSO via a flexible riser, which connects into the Petrobras gas export system. The bellmouth change-out operations consisted of replacing the bellmouths of each of the 8 production risers. The paper will focus on engineering design and offshore operation phases to implement the bellmouth change-out in a safe, cost effective manner.

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