The Prestige Wreck Fuel-Recovery Project

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper OTC 17534, "The Prestige Wreck Fuel-Recovery Project," by R. Hernan, A. del Corral, C. Berenguer, SPE, R. Paez, J. Sparrowe, and J. Moro, Repsol YPF, originally prepared for the 2005 Offshore Technology Conference, Houston, 2-5 May. This article is an overview of the recovery project to extract the hydrocarbons remaining in the wreck of the Prestige tanker. The ship, carrying approximately 77 000 tonnes of heavy fuel oil, broke up and sank in 3850-m-deep water in November 2002, 240 km off the northwestern coast of Spain. During the sinking, and for a period of several months afterward, a large amount of fuel was spilled, 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. Extraction of the remaining fuel was carried out in 2004 by use of large-volume aluminum shuttles. An innovative core-flow technique was used to extract this extremely viscous fuel (500 kPa·s at the shuttle offloading conditions) from the shuttles and offload it into a floating storage and offloading (FSO) vessel. Finally, bioremediation was used to accelerate the biodegradation of the remaining immobile fuel. Project Summary On 19 November 2002, the oil tanker Prestige broke up and sank in two parts. Approximately 37 000 tonnes of heavy fuel was believed to remain in the wreck, which continued leaking. The Spanish government commissioned a permanent solution for stabilizing the wreck and neutralizing its cargo. Potential solutions included the use of shuttle tanks to transport oil from the wreck to a surface container, pumping the oil to the surface by use of a riser system, and enclosing the whole wreck in a sarcophagus. Fuel viscosity at the wreck conditions was extreme (3 to 4×106 kPa·s), which, at this 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 in 2003. The plan approved by the Spanish government consisted of the following. - Develop work-class remotely operated vehicles (ROVs) to operate at 4000 m water depth. - Seal all remaining leaks. - Carry out data acquisition on the wreck and its fuel composition and mobility, as well as on the environment and the marine soil, to assist future interventions. - Test a batch-extraction scheme that used shuttle bags. - Perform basic engineering studies of confinement solutions as an alternative if the above scheme did not work. Sonsub was hired as the main contractor, and, in the spring and summer of 2003, it carried out an offshore campaign for the above program to establish the basis for the actual fuel recovery planned for 2004.