As the tanker Prestige languished on the sea bottom yesterday, international experts brainstormed over the possibility of salvaging 17.5 million gallons of fuel oil before it escapes from the stricken vessel and possibly spreads environmental havoc along the Spanish coast for years.
The technology needed to remove oil from a sunken ship is known and proven: a robot submarine, a six-inch suction hose, a hydraulic pump and a circular saw that can cut through a tanker's steel hull and reach the oil within.
The new wrinkle, however, is that no one has ever tried to empty a ship as far down as the Prestige -- 14,000 feet below the surface of the Atlantic Ocean off the northwest coast of Spain. At that depth, in water a few degrees above freezing, the oil will flow like molasses, if it flows at all. Removing it will not be easy.
"You have to suck it out like toothpaste from a tube," said Roger Elliott, general manager for the Americas for the Rotterdam-based salvage company SMIT. "It's a question of temperature and viscosity."
On the other hand, low viscosity means the oil may be less likely to escape in a single, catastrophic hydrocarbon bubble. Instead, it may trickle out over a period of years or decades, posing little or no threat to the environment.
"My guess is that if you did the economic analysis, you'd find out the strategy would likely be to leave the oil where it is but monitor it," said Malcolm L. Spaulding, professor of ocean engineering at the University of Rhode Island and chairman of a 1999 National Research Council study on "Spills of Non-Floating Oils."
Regardless of the decision, however, Bendt Nilsen, general manager for the Houston subsidiary Frank Mohn AS, a leading manufacturer of heavy-duty submerged pumps, said the home office in Norway had begun to discuss how to do the job.
"Including the time to think about the problem and make what we need, I believe we could be ready in three to six weeks," Nilsen said. "We have a very quick turnaround on being able to produce and develop equipment."
SMIT, as salvor, and Frank Mohn, as pump-maker, have been partners for several years on a specialized technology for deep-water oil and chemical salvage that combines cutting-edge innovation and bootstrap improvisation. "Every job is the same," Nilsen said. "But every job is different."
The SMIT-Frank Mohn method, used successfully several times but never on a wreck sunk as deeply as the Prestige, employs a robot submarine to carry a small but extremely powerful hydraulic pump and drill to the hull of a stricken vessel and fix it there like a limpet.
Elliott said salvors rig the pump with lights and cameras and tether it to the mothership by cable, with enough slack so that 15-foot seas on the surface leave the submersible motionless alongside the wreck.
The cable includes electric and hydraulic lines as well as a six-inch plastic pipe used to draw off the trapped oil at a rate of 300 metric tons (76,800 gallons) per hour. "Of course as viscosity increases, capacity goes down," Nilsen said.
And that's the rub. If the salvors are lucky and the oil flows, Nilsen continued, the drill first pokes a hole in the ship's hull at its lowest point and leaves a base plate in place there, so that water can get in but not out.
Then the drill bores a second hole high up on the side of the oil bunker and inserts the pipe. Ideally, the pump starts and the oil shoots to the surface. Water enters through the bottom hole to fill the emptying tank and keep it from buckling.
But suppose, as is most likely in this case, the oil does not flow. "There are several things we can do," Nilsen said. One solution would be to install a steam heater in the lower plate, and simply suck the oil from the top hole and funnel it back through the bottom hole across the heater until the recirculated oil becomes hot enough to transit the pipe to the surface.
Elliott also suggested running an electric coil into the top of the tank to heat the surface oil at the mouth of the suction hose. Both experts noted that the inside of the pipe could be lubricated with water, making the treacly "toothpaste" flow faster, or the oil could be spiked with mineral or vegetable oil to loosen it up.
"There are a lot of considerations, and a lot of different ways to solve the problem," Nilsen said. "But nobody has been hired to do the job yet. First you have to come up with a fund to pay for it."