Following the sinking of the "Prestige" oil tanker, several alternatives entered the fray, in order to recover the remaining fuel oil in the tanks.
This paper introduces an innovative alternative to achieve that goal, which was the contingency method planned by Repsol YPF in order to neutralize the fuel oil, in case the shuttle bag extraction technique were to prove itself invalid, or the quantity of fuel oil remaining inside the wreck was greater than expected.
The basics of the method comprise the design, fabrication and deployment of a steel canopy over the wreck bow of the sunken tanker, which lies on the seafloor at some 4000m water depths. This canopy should contain all the remaining fuel oil, providing enough margins to develop a subsequent recovery intervention with the aid of a Multi-purpose Subsea Construction Vessel (MSCV).
Repsol YPF, though in no way connected to the vessel or its cargo, was appointed by the Spanish government to recover the fuel remaining in the wreck.
The Repsol YPF Prestige Recovery Project has won the prestigious Energy Engineering Project of the Year at the Platts Global Energy Awards for 2004.
The "Prestige" oil tanker broke up and sank near the coast of Galicia in November 2002, giving rise to one of the worst environmental disasters in Spain's recent history.
Thousands of metric tonnes of heavy fuel oil were spilt into waters of the Atlantic Ocean, and soon afterwards washed up mainly over a large area of Spain's Northern coastline, causing the major environmental disaster.
As a significant amount of the original fuel oil (77,000 Tm) still remained in the wreck, at some 4,000 m water depth, the Spanish Government commissioned Repsol YPF to investigate an effective solution to neutralize the cargo.
One of the proposed solutions to limit further environmental damage resulting from further leakage of the trapped heavy fuel oil cargo; consisted of a two-phased fuel oil (a) containment and (b) recovery strategy. The first phase would involve the construction and deployment of a steel canopy known as the "Marquesina" over the "Prestige" wreck bow section. The purpose of this canopy was in the short term, to immediately contain any further fuel oil leakage from the hull. In the longer term the safe capture and containment of the fuel oil residing in the wreck, would allow sufficient time to develop a rapid fuel oil recovery operation, which minimised expensive MSCV, DP tanker and support vessels time, Figure 1.
With the canopy successfully installed on location, the fuel oil would be deliberately released by opening the hatches and by hot tapping additional holes in both the deck and hull plating. Thereafter, the fuel oil would exit and rise, under natural buoyancy until finally collecting in the underside of the canopy structure.
Only when all remaining fuel oil would be successfully liberated and safely contained in the canopy, would the second phase fuel oil recovery operation begin, e.g. next spring period.
