Abstract

This article is intended to provide a detailed overview of the recovery project devised to extract the hydrocarbons remaining in the wreck of the "Prestige" tanker. The ship, carrying some 77,000 Tm of heavy fuel oil broke up and sunk in 3850 meters water depth in November 2002, 150 miles off the north western coast of Spain. During the sinking, and for a period of several months afterward, a large amount of fuel was spilt ending up mainly on the shores of Galicia.

Repsol YPF, though in no way connected to the vessel or its cargo, was appointed by the Spanish government to recover the fuel remaining inside the wreck. Later Repsol YPF selected Sonsub as the main contractor.

The initial campaign, carried out in 2003, involved the design and construction of the tools required to operate a those depths, sealing off all remaining leaks in the wreck, conducting a comprehensive data acquisition and research campaign that included measuring the fuel remaining inside the wreck's tanks and carrying out a pilot test of a novel batch extraction method which involved the development of a safe system to perforate the wreck's deck and control the extraction of fuel.

The extraction of the remaining fuel was carried out in 2004 using large volume aluminium shuttles. An innovative core-flow technique was used to extract this extremely viscous fuel (some 500,000 centipoises at the shuttle offloading conditions) from the shuttles and offload it into a Floating Storage and Offload (FSO) vessel. Finally, a bio-remediation procedure to accelerate the biodegradation of the immobile fuel was implemented.

Details of the different aspects of the project are described in separate papers, see References.

The Repsol YPF Prestige Recovery Project has won the prestigious Energy Engineering Project of the Year award at the Platts Global Energy Awards for 2004.

Project Summary

On November 19th, 2002, the oil tanker "Prestige" broke up and sank in two parts some 240 km off the Spanish coast in approximately 3,850 m of water, spilling large amounts of fuel that polluted mainly the Galician shores. Around 37,000 Tm of heavy fuel were believed to remain in the wreck, which continued leaking fuel.

Repsol YPF was commissioned by the Spanish Government to find a permanent solution for stabilizing the wreck and neutralizing its cargo. Potential solutions studied included the use of "shuttle tanks" to transport oil from the wreck to a surface container, pumping the oil to the surface using a riser system and enclosing the whole wreck in a sarcophagus.

Fuel viscosity at the wreck conditions was extreme (3 to 4 million centipoise). This, together with the depth, precluded the use of conventional techniques.

Repsol YPF, with technical assistance from BP, Eni, Petrobras, Statoil and Total, outlined an action plan to be completed within 2003. The plan approved by the Spanish government consisted of:

  • Developing Work-Class ROVs to operate at 4,000 m depth.

  • Sealing of all remaining leaks.

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