The tanker Prestige, carrying 77,000 Tm of heavy fuel, sank in 3,850 m of water 153 nautical miles off the north coast of Spain in November 2002. The ship broke apart and, for several months afterward, large quantities of spilt fuel washed ashore in Galicia 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 remaining in the wreck. Repsol YPF subsequently selected Sonsub as its main contractor.
This paper describes the required operations performed during the final wreck fuel recovery project, mainly focusing on deepwater (up to 4,000 meters) and offshore operations. A project overview and details of other aspects of the project are described in separate papers, see References.
Innovative deepwater equipment and procedures were involved during these operations, both due to water depth and the atypical activities to be performed: several vessels required on the surface, simultaneous ROV operations in nearly 4,000 meters of water depth, the tapping onto the wreck's tanks, the transfer of extremely viscous fuel into specially designed shuttles, the recovery of these shuttles to surface and offloading them into a dynamically positioned FSO.
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 fact of performing such a vast amount of heavy-duty work at 4,000 m of water depth represented one of the main challenges of the project. This issue, connected with the new technology, risk management and the demanding need of protecting the environment, made this entire operation an amazing challenge for any working team. The paper illustrates how the operations were designed, which technical problems were faced and solved, and finally how the operations to recover 13,700 tons of fuel from 4,000m water depth were successfully completed.
The initial studies indicated that the innovative content of any solution adopted to solve the Prestige incident would require a substantial verification phase to ensure the feasibility. At the same time fuel was still leaking from the wreck and it was apparent that a survey would be required at the site to verify the actual conditions. It was also established that in order to have a reasonable availability for offshore operations, the activities would have to be concentrated between May and September when the meteo-oceanographic conditions were most suitable.
A two phase operational plan was therefore 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.
The first offshore operations started in the spring of 2003. The scope of this first campaign, carried out just two months after Sonsub had been selected to develop the innovative underwater equipment necessary, was to:
Verify that the equipment for the operations on the wreck, as well as for the extraction and recovery of the fuel were suitable to the task.