Sunken tanker may help cleanup in future accidents

A model of the leak dynamics of the oil tanker, Prestige, that sunk off the coast of Spain in 2002, may help assess recovery and cleanup methods for future tanker accidents, according to an international team of researchers.

“We believe that 14,000 metric tons (15,400 British tons) of oil were recovered from the tanker using the shuttle-bag system, and that between 16,000 (17,600) and 23,000 (25,300) tons of oil are still in the ship,” says Dr. Bernd J. Haupt, senior research associate, Earth and Environmental Systems Institute at Penn State.

From June to September 2004, a bagging method – the shuttle-bag system – that placed containers over the oil stream seeping out of the tanker, collected the leaking fuel. The impact of the sinking of the oil tanker is the focus of a study lead by an international team of researchers.

The Prestige is of interest because it sank in about 12,000 feet of water, deeper than most tanker wrecks, making full recovery of the oil impossible. Even though the tanker has, for the most part, stopped leaking oil, eventually, it will leak again.

“The remaining 30 percent of the oil is comprised of asphaltenes and resins which are not easily degradable,””says Haupt. “Normally, salt water would rust through the hull in about 23 years, but in this case, a bacteria that devours iron is present and it will take only 4 years before the wreck stats to leak again.”

With the variety of problems surrounding the Prestige, the researchers, who included Maria J. Marcos, Almudena Aguero, and Jose L. De Pablos, CIEMAT, Madrid and Antonio Garcia-Olivares, ICM-CSIC, Barcelona, developed a model that considered the depth of the wreck, how much oil was in the ship, the water and oil temperature at the ocean floor, the type of oil, ocean currents and the location and size of the cracks in the hull.

The Prestige is a single hull tanker and the force of the pressure at that depth partially crushed many of the compartments. By now, the oil has cooled to the temperature of the surrounding water, which is not cold enough to solidify the oil.

The model study accurately recreated the series of events that occurred in the release of the oil from the tanker, the team reported in a recent issue of Scientia Marina.

“This method can help us to deal with future wrecks,” says Haupt. “If another tanker sinks and we analyze it, we can determine how long it will take for most of the oil to leak out. If the time it takes to mount a confinement or pumping effort is longer than the time it takes to leak out, then there is no point in beginning the effort.”

One problem with the Prestige and other tankers is that it is common practice to underreport the amount of oil in a tanker to save on insurance costs. According to Haupt, the model, which is based on the reported amount of oil, could underrepresent the impact of the oil spill.

“We do not know what is going to happen with the wreck of the Prestige,” says the Penn State researcher. “We do not know what the new government of Spain is going to do or what will happen. However, this research has highlighted the fact that at this time, the economic and environmental costs are greater than those of the Exxon Valdez oil spill.”

Since the oil inside the tanks is expected to have been decanted, its solid part cannot flow to the bags. However, in the future, large fractures in the tanks, which will be produced by corrosion, will expose the remaining oil. These asphaltenes and resins may be transported by ocean currents when the hull is corroded and may become a future environmental problem, the researchers report.