Using Herders for Rapid In Situ Burning Of Oil Spills on Open Water. February 14, 2011

Transcription

1 Using Herders for Rapid In Situ Burning Of Oil Spills on Open Water February 14, 2011 Ian Buist SL Ross Environmental Research Ltd Belfast Rd. Ottawa, ON, Canada K1G 0Z4 Dr. Tim Nedwed, ExxonMobil Upstream Research Company P.O. Box 2189 Houston, TX ABSTRACT Since 2004, the main goal of R&D on herding agents (also called oil collecting agents) has been to determine their ability to enhance in situ burning of oil in ice concentrations too low for natural containment of the oil slick by the ice itself (i.e., ice concentrations between <10 and 60%). Unexpectedly, the results also indicate that the concept of in situ burning enhanced by herders has the potential of being extended to open water conditions. Herders were studied in the 1970s as an open water oil spill response technique but the goal was to provide containment for mechanical recovery. In this application herders were limited to relatively calm conditions because the herder itself dissipated quickly in higher seas allowing the slick to respread. This dissipation occurred over periods of tens of minutes: not enough time to allow skimming of the herded slick. In situ burning is a process that requires only minutes to implement using minimum logistics and equipment. Thus, the potential exists that in situ burning using herding agents could be an effective, rapid response technique in open waters both in polar and remote temperate regions. In the research, including fieldwork, on using herders for burning in drift ice, a considerable number of experiments were performed in open water conditions as an integral part of each test matrix. The data indicate that herders will work quite well to thicken fluid oil slicks for efficient in situ burning in quiescent open water conditions. However, there remain two issues requiring study: 1. Surfactant film persistence in a variety of open water sea conditions; and, 2. Suitability of the best cold-water herders for warmer water conditions. This paper documents the findings of the past laboratory, test tank and field burning experiments in open and near-open water conditions, and the historical field tests of herder use offshore in the 1970s to present the case for their use with in situ burning as a method of quickly responding to open water spills in remote areas. INTRODUCTION Since 2004, the main goal of the research on herders has been to determine their efficacy at enhancing in situ burning in ice concentrations too low for natural containment of the oil slick

2 by the ice itself (ice concentrations between <10% and 60%). In the research on herders in drift ice a considerable number of the experiments were performed in open water or trace ice conditions as an integral part of each test matrix, certainly enough to know that they will work quite well to thicken slicks for efficient in situ burning on quiescent cold seawater. The use of specific chemical surface-active agents, sometimes called oil herders or oil collecting agents, to clear and contain oil slicks on an open water surface is well known (Garrett and Barger, 1972; Rijkwaterstaat, 1974; Pope et al., 1985; MSRC, 1995). These agents have the ability to spread rapidly over a water surface into a monomolecular layer, as a result of their high spreading coefficients, or spreading pressures. The best hydrocarbon-based herding agents have spreading pressures in the mid-40 mn/m (milli-newtons per meter = dynes/cm) range, whereas most crude oils have spreading pressures in the 10 to 20-mN/m range. Consequently, small quantities of these surfactants (about 5 L per kilometre or 50 mg/m 2 ) will quickly clear thin films of oil from large areas of water surface, contracting the oil into thicker slicks. Herders sprayed onto the water surrounding an oil slick result in formation of a monolayer of surfactants on the water surface. These surfactants reduce the surface tension of the surrounding water significantly (from 73 mn/m to mn/m, or less). When the surfactant monolayer reaches the edge of a thin, fluid oil slick it changes the balance of interfacial forces acting on the slick edge and changes the balance of interfacial tensions causing the oil to contract into thicker layers. Herders do not require a boundary to push against and will work on open water. A conceptual drawing of the herding process in pack ice is shown in Figure 1. In their original application in the 1970s (to thicken slicks for subsequent mechanical recovery) herders were limited to relatively calm conditions because the herder itself dissipated quickly in higher energy sea conditions allowing the slick to re-spread. This dissipation occurred over periods of tens of minutes, which wasn t enough time to allow skimming of the herded slick. In situ burning is a process that only requires minutes to initiate and complete. Once ignited, the air being drawn into a large in situ oil fire by the combustion process will also contain the burning slick and thicken it further. Thus, there is great potential that in situ burning enhanced by chemical herders can be a very effective rapid response technique in ice-free waters both in the Arctic and in temperate regions. PAST RESEARCH ON HERDERS TO THICKEN OIL FOR BURNING The key to effective in situ burning is thick oil slicks. For application in loose pack or drift ice, the intent of recent research on herders has been to herd freely drifting oil slicks to a burnable thickness, then ignite them with a Helitorch. The herders work in conjunction with the wave dampening and the limited containment provided by the ice floes to allow a longer window of opportunity for burning. A comprehensive, multi-year, multi-partner research program to study the use of chemical herding agents to thicken oil slicks in order to ignite and burn the oil in situ in loose pack ice has been underway since As an integral part of the test matrix for each study, test of herders have been conducted on open water, including: 1. A very small scale (1 m 2 ) preliminary assessment of a shoreline-cleaning agent with oil herding properties was carried out to assess its ability to herd oil different oils on cold water and among ice (SL Ross 2004). One third of these tests involved cold water with no ice present and the positive initial results with shoreline cleaning agent led to further studies with more effective herders. 2. Small-scale (1 m 2 ) experiments were carried out next to explore the relative

3 effectiveness of three oil hydrocarbon-based herding agents in simulated ice conditions; followed by larger scale (10 m 2 ) quiescent pan experiments to explore scaling effects; small-scale (2 to 6 m 2 ) wind/wave tank tests to investigate wind and wave effects on herding efficiency; and finally, small ignition and burn tests (SL Ross 2005). Approximately half of the 1 m 2 tests, 30% of the 10 m 2 tests, two of five wind/wave tank tests and three of four small burn tests did not involve ice. The results showed that the U.S. Navy cold-water herder formulation (65% Span-20 and 35% 2- ethyl 1-butanol) performed as well or better on cold open water as it did in ice conditions, but that breaking waves caused the USN herder to become ineffective. 3. Experiments were done with the USN herder at the scale of 100 m 2 in the indoor Ice Engineering Research Facility Test Basin at the US Army Cold Regions Research and Engineering Laboratory (CRREL) in November 2005 (SL Ross 2007). None of the tests at CRREL were on open water; however, about 35% of the tests were conducted with only 10% ice cover. Tests with short, choppy waves in light ice conditions showed that these types of waves detracted from herder performance. 4. Experiments were undertaken with the USN herder at the scale of 1000 m 2 at Ohmsett in artificial pack ice in February 2006 (SL Ross 2007). None of these tests at Ohmsett involved open water. One test with long swells in light ice showed that herders can operate effectively in these types of waves. 5. A series of 20 burn experiments were carried out with the USN herder at the scale of 30 m 2 in a specially prepared test basin containing broken sea ice in November 2006 at the Fire Training Grounds in Prudhoe Bay, AK (SL Ross 2007) with fresh crude oil. Two of the burn tests were carried out on cold open water and the results were not noticeably different from those in broken ice. Again, tests with short, steep waves in light ice concentrations showed that the herder performance degraded in these conditions. 6. Field tests in pack ice in the Barents Sea were done in 2008 (Buist et al. 2010a). The second field experiment involving the release of 630 L of fresh Heidrun crude onto essentially open water in a large lead (Figure 2). The free-drifting oil was allowed to spread for 15 minutes until it was far too thin to ignite (0.4 mm), and then USN herder was applied around the slick periphery. The slick contracted and thickened for approximately 10 minutes at which time the upwind end was ignited using a gelled gasoline igniter. A 9-minute long burn ensued that consumed an estimated 90% of the oil. 7. Studies on better herding surfactants were completed between 2008 and 2010 (Buist et al. 2010b). In the laboratory testing, all of the Dynamic Film Performance and 1-m 2 pan tests were conducted with no ice, as were half of the 10-m 2 tests. The results on open water showed that different herders performed better at different temperatures and water salinities and that all lost their effectiveness over time in dynamic conditions. Three of 15 larger-scale experiments with silicone-based surfactants at CRREL in 2009 were on open water and confirmed that the A108 silicone herder outperformed the USN and the A004-D silicone herder in these conditions. The A108 silicone herder also performed as well on cold open water as in ice. HISTORICAL OPEN WATER FIELD EXPERIMENT DATA Herders were studied in the 1970s as an open water oil spill response technique but the

4 goal was to provide containment for mechanical recovery. In this application herders were limited to relatively calm conditions because the herder itself dissipated quickly in higher seas, allowing the slick to respread. Field tests of herders on open water with a 25-gallon fuel oil slick in Chesapeake Bay (Garrett and Barger, 1972) and a 5-ton crude oil slick in the North Sea (Rijkwaterstaat 1974) have shown them to retain their efficacy for several hours in winds of up to 6 m/s (12 knots) and up to 2-m (6-foot) seas, providing the herder monolayer was periodically replenished. FUTURE WORK Warm Water Herding Agents The recent research on herders to promote in situ burning in ice has focused on identifying herding agents that perform with relatively fresh, fluid crude oils and distillate fuels on cold water. The original US Navy study (Garrett and Barger, 1972) identified better surfactant/solvent combinations at room temperature. Other commercial herder recipes e.g., OC-5, Shell Herder, etc. - may very well outperform the cold-water USN herder in more temperate waters. Also, the silicone surfactants identified as the best for cold-water use may not be the best for warmer waters. Additional research is needed to identify herding agents that perform well in warm water conditions. Ohmsett Testing of Herder Persistence in Waves Surfactant film persistence (i.e., how long herding agents will maintain burnable oil slicks as a function of sea state) and to what degree periodically replenishing the film can counteract this needs to be studied. This could be investigated at Ohmsett, taking advantage of the facility s newly upgraded wave making capabilities. Although waves generated in the Ohmsett tank do not exactly mimic ocean waves, recent studies of Ohmsett waves show that they can be related to young seas (Veron et al. 2009). The results of experiments on herder monolayer persistence in different wave environments at Ohmsett, combined with historical offshore field data, will be useful in predicting herder monolayer persistence at sea. SUMMARY Herding agents were studied in the 1970 s as a method of thickening oil slicks prior to mechanical recovery. Unfortunately, it was discovered during field tests that herded slicks began to respread in tens of minutes in all but relatively calm seas. They were never applied during an actual offshore spill because mechanical recovery requires longer periods to implement. A research program initiated in 2004 to advance oil spill response in ice has found that herding agents persist long enough to enable in situ burning of relatively fresh, fluid oils in broken or drift ice. Many open water tests were completed during this work. These tests provide evidence that herding agents can enable in situ burning in open water because the process can be implemented quickly and requires only minutes to complete. Although additional research is needed to identify optimal herder formulations for warm water environments and to define the sea conditions when herders can be used, the recent work demonstrates that chemical herders used in quiescent open water can enable in situ burning without the need for fire-resistant booms

5 ACKNOWLEDGEMENTS The research studies described in this paper were variously funded by the Bureau of Ocean Energy Management Regulation and Enforcement (BOEMRE), U.S. Department of the Interior; ExxonMobil Upstream Research Company, and the SINTEF JIP Oil in Ice funding consortium (Shell, Statoil, ConocoPhillips, Chevron, Total, Agip KCO and the Norwegian Research Council). The opinions, findings, conclusions, and recommendations expressed are those of the authors and do not necessarily reflect the views of BOEMRE, ExxonMobil, SINTEF or their funding partners, nor does mention of trade names or commercial products constitute endorsement or recommended use. REFERENCES Buist, I. and E. Twardus, Burning uncontained oil slicks: large scale tests and modelling. Proceedings of the 8th Annual Arctic Marine Oilspill Program Technical Seminar. Environment Canada, Ottawa, pp Buist, I., S. Potter and S.E. Sørstrøm. 2010a. Barents Sea Field Test of Herder to Thicken Oil for In situ Burning in Drift Ice. Proceedings of the Thirty-third AMOP Technical Seminar on Environmental Contamination and Response, Environment Canada, Ottawa, pp Buist, I., G. Canaveri and T. Nedwed. 2010b. New Herding Agents for Thickening Oil Slicks in Drift Ice for In situ Burning. Proceedings of the Thirty-third AMOP Technical Seminar on Environmental Contamination and Response, Environment Canada, Ottawa, pp Garrett, W.D. and W.R. Barger, 1972, Control and Confinement of Oil Pollution on Water with Monomolecular Surface Films. Final Report to U.S. Coast Guard, Nov 1971, Project No /4.1 (also reprinted as U.S. Navy Naval Research Laboratory Memorandum Report 2451, June 1972, AD ). Marine Spill Response Corporation (MSRC), 1995, Chemical Oil Spill Treating Agents, MSRC Technical Report Series , Herndon, VA. Pope, P., A. Allen and W. G. Nelson, 1985, Assessment of Three Surface Collecting Agents during Temperate and Arctic Conditions. Proceedings of the 1985 Oil Spill Conference, API/EPA/USCG, Washington, DC, pp Rijkwaterstaat, 1974, Shell Herder Trials, Report to the Dutch Ministry of Transport, Gravenhage, Holland. SL Ross Environmental Research, 2004, Preliminary Research On Using Oil Herding Surfactant To Thicken Oil Slicks In Broken Ice Conditions, Report to ExxonMobil Upstream Research, Houston. SL Ross Environmental Research, 2005, Small-Scale Test Tank Research on Using Oil Herding Surfactants to Thicken Oil Slicks in Broken Ice for In situ Burning, Report to ExxonMobil

6 Upstream Research, Houston, TX SL Ross Environmental Research, 2007, Mid-scale Test Tank Research on Using Oil Herding Surfactants to Thicken Oil Slicks in Broken Ice, Report to MMS, ExxonMobil Upstream Research Company, Agip Kashagan North Caspian Operating Company, Sakhalin Energy Investment Company and Statoil ASA, Herndon VA. Veron, F., SL Ross Environmental Research and MAR, Inc., Surface Turbulence Measurements at Ohmsett. Report to U.S. MMS, Herndon, VA

7 Figure 1. Conceptual drawing depicting the herding process in drift ice. Herders sprayed on water around perimeter of slick Herders rapidly spread to form monolayer Herders change surface chemistry of water forcing slick into smaller area Figure 2: Free-drifting slick herded by USN burning in lead