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Spill response in ice laden waters
Some new technologies are addressing the challenges of recovering oil spilled in sea ice conditions in Arctic offshore areas
Alan Bailey Petroleum News
Responding to an oil spill in ice-laden waters in the Arctic offshore is different from an offshore spill response in warmer climes. And on March 29 during the Alaska Oil Spill Response Symposium Vince Mitchell, Lamor Corp. executive vice president, talked about some new technologies that have been developed for recovering oil from the sea, in situations where sea ice is present. Mitchell and some other speakers at the symposium commented on heightened oil spill risks in the Arctic offshore, as vessel traffic in the region increases.
Mitchell said that although there can be challenges in dealing with ice when responding to an Arctic spill, some features of ice laden waters can work to the responders’ advantage: There may be less oil evaporation, less spreading of the oil, and less wave action.
Response strategies There are three general approaches to dealing with an offshore oil spill: mechanical containment and recovery of the oil; in situ burning of the oil; and the use of oil dispersants. Some combination of these approaches may be required, depending on the circumstances. However, in Arctic conditions a recovery technique must be robust, simple, proven and adaptable to the situation. In-situ burning and dispersant use have associated permitting requirements - mechanical oil recovery appears set to remain a viable option, Mitchell suggested.
Mechanical recovery involves the use of boom for containing an oil slick, and the operation of skimmers, devices that can remove oil from the water for transfer to a holding tank.
Arctic adaptations to mechanical recovery equipment include various arrangements for applying heat, including the use of hot water or steam for heating hoses, double hulled skimmer designs that incorporate heating arrangements; and heated storage tanks, Mitchell said.
For the non-mechanical recovery of oil, there has been some very promising research into the use of chemical oil herders. A herder, added to an oil slick, causes the oil to aggregate thickly, thus making in-situ burning, for example, more efficient.
Tactics in ice Whereas a spill response in open water typically involves the deployment of long lengths of containment boom, to deflect, concentrate and enable recovery of the oil, the presence of sea ice undermines the practicalities of this approach. As ice concentrations increase, the recovery technique tends more towards the collection of pockets of oil between ice floes. And in heavy ice conditions different techniques and specialized skimmers are required, Mitchell said.
A rope mop skimmer, an oil skimmer with oil attracting material on a chord that cycles through the water, has been the technology of choice for many years for pulling oil from water between ice, Mitchell said. Lamor has developed a vibrating grid arrangement that can separate oil from ice as part of the skimming system. These specialized skimmers are installed on modified oil spill response vessels, Mitchell said.
Lamor also has what is calls an oil recovery bucket, a device that is lowered into the water from a crane and contains a rotating skimmer brush for mopping up the oil. This device, which comes in a variety of sizes, can prove effective in dealing with pockets of oil in broken ice conditions, Mitchell said.
Stern mounted systems The Finnish Environment Institute has developed what it calls a stern brush, a brush skimmer deployed from the stern of a vessel. The vessel moves slowly astern, using its prop wash to draw oil into the skimmer, Mitchell said.
Lamor has also developed a stern-mounted skimming system called the Sternmax. This has a heating system, a grate that blocks the ice and a hydraulic system for dumping ice off the grate. The device, which can be operated remotely, can break through 1.5 meters of ice, Mitchell said. Highly efficient, oil attracting skimming material minimizes the amount of water recovered along with the oil, thus reducing the amount of water that ends up stored with the recovered oil.
Oil under ice Recovering oil from under ice presents a particular challenge. A recent project, the Ice Management and Oil Recovery project, used dyes in water to test the efficiencies of different techniques for using skimmers for the recovery of oil trapped under sea ice. Contrary to what might be expected, the research determined that the use of an icebreaker to crush the ice before skimming the oil is not the most effective technique. Instead, it is better to run the vessel onto the ice, down current, to then use a skimmer to draw oil from under the ice. If necessary, it is possible to use the vessel thrusters at low power settings to draw the oil under the ice towards the skimming device. In one test it proved possible to draw dye from a distance of 80 meters from the skimming device in about 20 minutes, Mitchell said.
Other possibilities for future technologies for a cleanup under ice include the use of remotely operated vessels, and the design of skimmers that can function under ice, Mitchell said.
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