Task 1. Using Herders to Enhance Mechanical Recovery of Oil in Pack Ice

Field deployment tests of booms and skimmers in broken ice conditions in the Alaskan Beaufort Sea highlighted the severe limitations of conventional containment and recovery equipment in even trace ice (Bronson et al. 2002). The main problem is that booms, deployed to collect and concentrate oil for effective skimming, also collect and concentrate ice pieces that quickly render the skimmers ineffective. The research on using herding agents to thicken slicks for in situ burning has shown that they can significantly contract and thicken oil among ice, without concentrating the surrounding ice. This could be beneficial to mechanical recovery. In fact, as a skimmer removes oil from the center of a herded slick, the action of the herding agent may cause the slick to continuously contract towards the skimmer, eliminating the need to move the skimmer around to contact all the oil. However, it has been observed that the active ingredient in herding agents (the surfactant) renders sorbent pads less hydrophobic and their water retention increases considerably. This could be a significant detriment to oleophilic skimmers such as drums, discs and rope mops whose recovery surfaces contact herding agent. This should not be an issue with other skimmers types such as weirs and vacuums.

Experiments were successfully conducted February 9-20, 2009 at the Ohmsett - The National Oil Spill Response Research and Renewable Energy Test facility to explore the capabilities and limitations of using herding agents to thicken oil in loose pack ice for recovery by skimmers.

In late May 2008, the Principal Investigator participated in an intentional oil spill offshore Svalbard, Norway. Approximately 1,500 liters of crude oil were released onto the waters surface and allowed to spread for one half hour. A small amount of chemical herder was applied on the outside of the slick and allowed to contract the slick. The slick was intentionally ignited and allowed to burn. It is estimated that the burn efficiency was approximately 90 percent.

Task 2. Using Herders to Clear Oil Slicks in Salt Marshes

A parallel to the situation in pack ice exists in salt marsh environments: access for mechanical recovery equipment is almost non-existent due to concerns over damaging the marsh substrate. This task will involve preliminary laboratory experiments in small-scale simulated marshes to determine if chemical herders might play a role in clearing spilled oil from the marsh.

Experiments using small scale simulated marsh environments were successfully conducted in September 2008 to determine if chemical herders might play a role in clearing spilled oil from the marsh.

Task 3. Herders to Improve Operational Efficiency of Dispersant Operations.

The application of a herding agent around the periphery of a slick just prior to it being treated with dispersant would cause the slick to contract into much thicker oil, covering a much smaller area with a more uniform, and predictable, thickness. This would allow more precise application of dispersant to a smaller area of oil at a more predictable dosage. Herders will contract free-spreading oils with thicknesses ranging from <1 µm to 1+ mm into slicks of ~1 to 4 mm thickness, eliminating the sheen overdosing problem and greatly aiding the thick slick under-dosing problem. This offers the possibility of significantly improving dispersant targeting. Slicks that have spread to «1 mm thickness could be shrunk and thickened with a chemical herder applied with a helicopter-slung bucket delivery systems, or vessel-based delivery systems, then treated with dispersant from ships or aircraft. Another possibility is the application of herding agents around slicks in calm seas to prevent them from spreading until the wind picks up and breaking waves (necessary for effective chemical dispersion) appear.

Task 1. Laboratory and Ohmsett experiments on the use of herders to enhance mechanical recovery in drift ice showed:

1. The use of herders in drift ice conditions could potentially improve the Oil Recovery Rate and Oil Recovery Efficiency performance of weir skimmers by factors of 2 to 10; however, the oil thicknesses produced by the herder were too low to permit optimal performance of the weir skimmer.
    
2. No significant improvement was measured in the performance of a disc skimmer in herded slicks compared to unherded slicks.

Task 2. Results from salt mash experiments showed:

1. In none of the static tests did the herder clear the oil completely from the marsh plants.
    
2. In some tests the herder caused the oil slicks to contract in size sufficiently to significantly reduce the oiled area of the marsh; however, even in these cases, there remained a ring of oil at the waterline around the originally oiled stalks of the marsh plants.
    
3. In all cases, after herder had been added, the slicks were thick enough to support ignition. This is a significant finding, since even though the herder did not clear the oil out of the marsh plants; it could contract the oil sufficiently to allow in situ burning.

Task 3. Results on using chemical herders to improve operational efficiency of dispersants:

1. The use of herders on an oil slick did not detract from the effectiveness of chemical dispersant application.
    

2. Using herders to contract slicks on open water can improve the operational efficiency of dispersants applied by vessels.
    

3. Herding a slick to be sprayed with dispersants from aircraft could reduce operational efficiency (by wasting large amounts of the dispersant). MMS has accepted the final report for this project.