PRESTIGE OIL RECOVERY FROM THE SUNKEN PART OF THE WRECK
Massimo Fontolan, Sonsub Ltd., Robin Galletti, SATE srl.
Introduction
This lecture deals with the equipment developed and the experience gained during the performance ofoperations carried out over a number of months during both the summer of 2003 and 2004 in water depths ofnearly 4,000 meters, for the recovery of the fuel contained in the tanks of the Prestige tanker. Repsol YPF
was appointed by the Spanish government to recover the fuel remaining in the wreck and subsequently
selected Sonsub as the main contractor.
The sinkingIn November 2002 the single-hull tanker Prestige sank at a distance of about 240 km (130 nautical miles)
from the North West coast of Spain off Galicia, splitting in two halves 1.9 nautical miles apart. The bow cameto rest in 3,830 metres water depth, while the stern came to rest in 3,565 metres water depth.
stThe 1 distress signal was sent on the 13
November 2002

ththNovember 2002, while the ship sank in two parts on 19

Initial activities
Prior to the actual project for the recovery operations, a number of activities were performed. Theseincluded:• During the month of December 2002 the Nautile mini submersible was engaged to perform preliminary
survey and leak plugging of the wreck• The Spanish Government appointed a Scientific Advisory Committee to advise as to the most suitable
solutions to be adopted• A large number of proposals, including one by Sonsub, were analysed by the Scientific Advisory
Committeeth• In 14 February 2003 the Spanish Government entrusted Repsol YPF with the study of the technicalviability, and following this with the management of the development of the necessary technology andthe recovery operations.
• 3 ‘Doability studies’ were assigned, two to Sonsub and one to Seal Engineering to develop the concepts
considered the most interesting. These were to be completed in three months.
Technical challenges
The main technical challenges that were faced were:• The 3,830 metres water depth. This was well beyond the state of the art for workclass ROVs, as well as
all the required equipment. Previous wrecks that had required similar recovery (e.g. Erika) were in diverdepths• Viscosity of 5 million cSt. This created a major challenge for the transfer of the oil both from the wreck tothe surface, and for the transfer to shore• The very tight schedule. During the 2003 operations, it was a requirement to design, construct and test
the innovative solutions and equipment developed within September 2003. The contract for this wasplaced in May 2003
Selection of Sonsub
Repsol YPF was appointed by the Spanish government and selected Sonsub as the main contractor, firstlyfor the doability studies, then for the innovative equipment development, then for the 2003 survey andverification operations, and finally for the 2004 full recovery. These contracts had the following schedule,
which again illustrates the rapidity with which the activities had to be performed:• March 2003, Sonsub selected to perform the doability studies on:o Shuttle recovery systemo Coffin to confine the wreck• April 2003, Sonsub selected to develop and construct:o Tapping tools
o Extraction valveso Water injection system

••May 2003, Sonsub selected to perform:o Survey of the wrecko Plugging of leakso Verification testing of shuttle concept
February 2004, Sonsub selected for complete recovery of a target 11,100 tonnes of oil

Equipment developed
The following main new items of equipment had to be developed, tested and employed for the recovery
operations:• Heavy work class ROVs for 4000 m water depth• Measurement systems to define residual oil• Beam sensors for positioning• Tapping tools for 700 mm openings in tanks• Anchored valve systems over openings
3• Shuttles of 350 m volume• Transferral of oil from shuttles with ‘core flow’ technology
The ROV for up to 4000 metres
Prior to this project, the INNOVATOR™ had a proven track record of performance and reliability operating on
Deep-water Projects up to 3,000 m. The Prestige Project presented a ground breaking challenge whichinvolved a modification program to upgrade all aspects of the Innovator ROV system to operate continuously
in 4,000m of water.
This was achieved using the existing 3000 m umbilical to the Tether Management System, and the 1200 m
tether already developed for touch down monitoring of pipelines. The configuration was changed in that thetether was deployed vertically rather than horizontally.
Due to the inherent capabilities that the INNOVATOR™ already had as well as its track record, the actual
items of equipment that had to be modified to achieve the 4000 m water depth target were limited to thefollowing principal systems:• Buoyancy• Manipulators• Cameras and lights
The testing of the ROVs was carried out as the first activity of the 2003 campaign, and was essetial to thefeasibility of performing any of the operations on the wreck.
Plugging of leaks
Following the successful tests on the INNOVATOR ROVs, operations commenced on the survey of thewreck, following which the plugging of the leaks still present from the various tanks was carried out, using a
number of different methods and tools.
Remaining fuel on the wreck
The oil measurement analyses performed during the 2003 campaign indicated that the remaining fuel oil
could be estimated at:• 13 000 Tm in the bow, located in port and starbord tanks, while the central tanks were effectively empty,
and• 700 Tm in the stern
Polar Prince and FPSO ODIN on site
The Polar Prince, a multi purpose DP2 class vessel operated by Sonsub, was adopted for both the 2003 andthe 2004 operations. This vessel was able to deploy up to 3 INNOVATOR ROVs to full depth simultaneously,
as well as all the necessary tapping tools, extraction valves and water injection systems.
The MST/FSO Odin was the designated oil recovery vessel. She is a Multi-purpose Shuttle Tanker vessel
with DP 3 dynamic positioning capabilities used as a Floating Storage and Offloading unit. She stocked thePrestige oil cargo once recovered to the surface and discharged from the shuttle tanks.

ROV performs beam sensor operations
A deck structural ultra sonic beam detection and plate thickness system was used to map the location where
the extraction valves were to be installed.
Marking of hot tapping locations
The locations for the installation of the tapping tool were then marked.
Positioning of tapping tool
Hop-tapping and extraction valves installations were performed on each of the four cargo tanks within thewreck bow section.
Tapping tool
The tool, which carries the extraction valve, is provided with an anchor bolt unit (6-off per system) to lock thevalve to the deck before starting the trepanning operations. The centre of the tool carries the trepan tool for
cutting 700mm holes. The system is operated by ROV through a dedicated IHPUExtraction valve
The design of the extraction valves were particularly focused on safe recovery operations and each valve
included failsafe shut -down systems as necessary to ensure that oil spills were avoided during the extraction
process. Each valve includes a double gate system on top and bottom. The bottom gate is operated by ROV
torque tool while the top one is either operated by ROV or can close automatically through a “fuse-bolt”
system broken by the force exerted when the shuttle tank is completely filled with oil.
Water injection system
During the flow of oil from the cargo tanks to the shuttle tanks, it was necessary to ensure the free entry ofwater into the lower part of the tanks to replace the escaping oil. For this purpose, a dedicated water
injection system was developed composing of water injection casings being installed via the Prestige deckhatches.
Shuttle during construction
Each shuttle tank is composed as follows:• A main aluminium body with a diameter of approx 5.3m and an overall length of approx 23m, suitable totake up to a maximum of 350 m3 of oil;
• A bottom interface provided with an ROV operable door to allow flowing of the oil from the oil extraction
valve into the shuttle tank;• A top interface with two ROV operated gate valves system and a mechanical interface to the riser
termination unit;• A pull down winch located on the top section of the shuttle tank to allow connection and controlled final
approach/release from the oil extraction valve;• Suitable buoyancy installed externally to the shuttle tank to have it buoyant and allow controlled
transportation through the water column by using the dedicated shuttle handling equipment.
Shuttle towing
Following completion of extraction valves’ installation, the shuttle tanks were towed offshore and prepared
for installation.
Shuttle deployment
The shuttle tanks were designed to be continuously buoyant with the descent and recovery operation
regulated and controlled by means of ballast chains. They are deployed to the Prestige wreck inapproximately 4 hours time, connected to the extraction valve assembly with a secondary connection to asafety anchor dead weight.

Shuttle winch system
Once deployed and connected to the pre-installed extraction valves, final positioning of the shuttle to enablesafe oil extraction is achieved via the operation of an ROV operated mechanical winch which is an integral
part of the shuttle.
Oil filling
The shuttle lower door assembly can then be opened again via ROV int ervention in preparation for thegravity entry of oil from the extraction valve.
Oil flow through valve and Shuttle being filled
During the extraction process the flow oil is controlled by ROV operation of the double gate extraction valve,with again failsafe systems to ensure overfilling is avoided.
Shuttle recovery
When the shuttle was approximately 60m WD, a riser assembly is lowered from the Odin and connected tothe shuttle.
Shuttle top interface to riser
The top interface connects to the riser termination unit and has two ROV operated gate valves to permit theoil to be pumped into the riser
Riser termination unit
The riser/pump assembly system is made up of a number of different components. These are:
• An handling winch;• A 6” flexible hose (riser);• A riser termination unit provided with a pump and a mechanical interface allowing to dock and lock onto
the shuttle tank top interface:• A service hydraulic bundle to allow operation of the riser termination unit from the surface.
Oil transfer to FPSO via Core Flow
One problem faced during the engineering phase was the fuel discharging operation. This was a point ofgreat concern because, given the very high oil viscosity, it initially seemed very difficult to pump the fuel outof the shuttle for a route of about 60m length from the shuttle riser connection to the Odin tank. The adopted
innovative “Core Flow” solution proved highly successfully and a significant contribution to the overall
success of the project. In effect water is pumped into the riser during the discharging in such a fashion as toform an outer sheath around the oil, giving birth to a so called core flow where the oil flows inside the waterfilm. This latter functions as a “lubricant”, i.e. it reduces the friction losses between the highly viscous oil andthe riser walls. With this method, by using a “standard” pump mounted at the bottom end of the riser it ispossible to pump the oil up to the Odin tank.
Bacteria injection
The final phase of the project consisted of bioremediation nutrients injection. The rate at which microorganisms naturally present in the water and in the oil actively consume fuel-derived toxic compounds canbe greatly increased by the addition of nutrients. This solution has been adopted for all tanks on the Prestige
where some oil still remains after the operations.
Prestige key dates
The following dates summarise the project development:• March to May 2003 Concept developed• May to July 2003 equipment for operations in 3830 m designed, constructed and tested• October 2003, first cargo of 100 tonnes recovered with shuttle concept• December 2003 to April 2004, procedures and equipment for industrial recovery completed• June to October 2004 complete remaining cargo of 13,400 tonnes of oil recovered

Sonsub Capabilities
Sonsub has established itself as having:• Unique deepwater intervention capability up to 4000 m water depth• Marine spread resources, operating 8 vessels• State of the art ROVs, with a total of 58 vehicles operated• Underwater operations experience• Innovative, project specific, equipment development• Experience from the Prestige project• Access to a worldwide group with such as Saipem that can support all its activities
Conclusion
The recovery of the fuel from the Prestige wreck, although considered by salvage experts as impossible atsuch a depth, was completed:•within schedule•
within budget•
without any environmental pollution•
within any incidents or accidents