Mooring and Anchoring Systems Developed in Marlin Field
Authors: Barusco Pedro 
Published: October 2008

Petrobras, due to the location of its reservoirs in very deepwaters, as the giant Marlin Field, has always been involved in the development of new technologies of mooring systems for floating drilling and production units.

The paper addresses the most important achievements of Petrobras and their equipment and services suppliers related to mooring technology during the development of Marlin Field.

Some of the most significant innovations of the mooring technology are shown, as the development of synthetic ropes, anchors with capacity to withstand vertical loads and the tautleg systems.

Among several mooring system installations Petrobras has been performing in deep waters, some deserve special attention and are addressed in the article. The world's first mooring system installed with synthetic legs in Marlin South Field, the first taut-leg system of the world installed in Marlin Field, the first use of vertically loaded anchors and the taut - leg in FPSO.

The last part of the article addresses the new developments for mooring systems that Petrobras considers most relevant for future application in ultra deep waters.

Introduction

When Petrobras discovered Marlin Field in 1984 it could by no means imagine it was discovering a huge laboratory for the development of very deep water production technologies, mainly when it comes to mooring systems.

The proven technology available in the beginning with the use of high holding power anchors, and steel cables allowed moorings in water depth under 1000 m.

We noticed that the systems available at the time were not optimized because nowadays we use much lighter and much cheaper and easier to install systems.

Several areas of mooring development could be mentioned: An increase in the holding power of the anchors; anchors with capacity of absorbing vertical loads; foundation alternatives such as, suction piles, grouted piles, torpedo piles; improving the process of production and increasing the resistance capacity of the steel for chains; new types of steel cables (spiral-strand); improving the corrosion resistance of cables; development of synthetic ropes; taut-leg anchoring system; Differentiated Compliance Anchoring System - DICAS, are some of the improvements that allowed cost reduction and increased the systems mooring capacity.

It would be impossible to consider all developments in a single article. For this reason we selected the most important aspects to include in this paper especially those that had a big role in the production of the giant Marlin Field.

Among the things to be discussed, the HHP anchor + chain + steel wire + Chain system, anchors for vertical loads, synthetic cables and taut-leg system were selected. Figure 1 shows the production systems already installed in Marlin and Marlin South and those to be implanted.

Figures 2 to 7 show some pioneer systems of Marlin field used in deep water and those worthy of mentioning.

HHP Anchor + Chain + Steel Wire + Chain System

Previously, the mooring system used chains only. The first measure taken to increase water depth was the introduction of steel cables called extension wires.

We thought that this system could be used in water depths around 1000 m, but we encountered difficulties in the installations, making the anchor handling vessels more complex and more expensive.

We observed though that this technology was already at it's limits and that a conceptual change of the anchoring system was required.