Operations in 4000 m Water Depth: Prestige Wreck Fuel-Recovery Project
Authors: Denney Dennis 
Published: February 2015

This article, written by Technology Editor Dennis Denney, contains highlights of paper OTC 17557, "Operations in 4000-m Water Depth for the Prestige Wreck Fuel-Recovery Project," by G. Corbetta, Sonsub A/S; A. del Corral, Repsol YPF; J. Ewen, Sonsub Ltd.; and R. Paez and I. Rodriguez, Repsol YPF, prepared for the 2005 Offshore Technology Conference, Houston, 2-5 May.
The tanker Prestige, carrying 77 000 tonnes of heavy fuel oil, sank in 3850 m of water 240 km off the northwestern coast of Spain in November 2002. The ship broke apart, and, for several months afterward, large quantities of spilled fuel oil washed ashore in the Gallaecia region of Spain and elsewhere. Repsol YPF, although in no way connected to the vessel or its cargo, was appointed by the Spanish government to recover the fuel oil remaining in the wreck. This paper describes operations performed during the fuel-oil-recovery project, focusing mainly on deepwater and offshore operations. Innovative deepwater equipment and procedures were used in tapping into the wreck's tanks, transferring extremely viscous fuel oil into specially designed shuttles, recovering these shuttles to surface, and offloading them into a dynamically positioned floating storage and offloading (FSO) vessel.

Introduction
Initial studies indicated that the innovative content of any solution adopted to solve the Prestige incident would require a substantial verification phase to ensure feasibility. At the same time, fuel oil was still leaking from the wreck, and it was apparent that a survey would be required at the site to verify the actual conditions. Also, for reasonable availability of offshore operations, activities would have to be concentrated between May and September, when the meteo-oceanographic conditions were most suitable.
Therefore, a two-phase operational plan was implemented, with the most urgent activities being targeted for the summer of 2003 and the complete remedial operations being targeted for the summer of 2004.
2003 Campaign. The first offshore operations started in the spring of 2003. The scope of this first campaign included the following.Verify that the equipment for the operations on the wreck, as well as for the extraction and recovery of the fuel oil, was suitable to the task.Prepare a suitable working spread to operate in diverless construction mode in 4000 m water depth.Repair any remaining sources of leakage.Assess the remaining fuel-oil quantity in the cargo tanks.Implement a comprehensive survey and data-acquisition program.Execute a prototype fuel-oil extraction (target 100 m3) to qualify the selected method for fuel-oil extraction.
The second phase of the project began in December 2003 to design, fabricate, and test all tools and equipment by no later than the end of April 2004. This tight schedule, to allow the start of the offshore operations by the beginning of May 2004, was one of the key challenges of the project. It was mandatory to complete the mobilization of the whole spread during the first half of May 2004. The extracting of more fuel oil than the planned 11 100 m3 was described in the article "The Prestige Wreck Fuel-Recovery Project" JPT (June 2005) page 58.