Mechanical Recovery of Oil in Ice
The goal of mechanical recovery is to remove oil from the surface of water using specially designed recovery (skimming) devices and to store the recovered fluids until they can be safely disposed or recycled. Recovery devices are most effective on thick slicks; hence containment booms are used in open water and very open ice cover to contain and concentrate and oil slick. In higher ice concentrations, the ice itself acts as a barrier to limit the spreading and contain the oil.
Many decades of experience with mechanical recovery under cold-climate conditions around the world have advanced the understanding of the recovery process and led to the development of proven response tactics and specialized equipment. Several configurations of ice-capable response vessels, both with built-in and over-the-side or stern recovery equipment are currently in operation. Azimuthal Stern Drive (ASD) vessels are invaluable for arctic oil spill and emergency response due to their high manoeuvrability in ice and ability to effectively support both mechanical recovery and vessel-based dispersant operations.
High-capacity arctic skimmers have been developed and tested for the recovery of oil in ice while operating at low temperatures. Advances with specialized cold climate skimmers include improved oil and ice processing, the ability to handle larger volumes of cold viscous oils and oil/ice mixtures with low water uptake, and the heating of critical components to prevent freezing. Various viscous oil pumping systems and techniques have also been developed to facilitate efficient transfer of cold and viscous mixtures of oil water and small ice pieces.
Planning for mechanical recovery in arctic waters should consider the logistical and environmental impacts associated with all phases of the response operations. Mechanical recovery is one of several viable response techniques available for arctic spill response when used appropriately.
As with any other tool, any final decision on its use needs to balance potential effectiveness against possible impacts, while recognizing the inherent limitations associated with variable ice conditions, remote area logistics and waste disposal sensitivities.
Mechanical recovery is a well-practiced response technique used under a variety of conditions around the world. Success depends upon the availability and rapid deployment of appropriate equipment and personnel, as well as an ability to gain safe access to the oil to allow recovery. This technique is most suited for small to moderate sized operational spills under relatively calm weather conditions in open water or very open drift ice as well as small localized small spills contained in closer pack ice. Considering that the vast majority of spills are small, and that most areas being considered for petroleum exploration and development have long periods of ice-free conditions, mechanical recovery will continue to serve as an important response tool in the Arctic.