THE TECHNOLOGY WINDOWS-OF-OPPORTUNITY FOR MARINE OIL-SPILL RESPONSE AS RELATED TO OIL WEATHERING AND OPERATIONS

This paper identifies and estimates time periods as 'windows-of-opport unity' where specific response methods, technologies, equipment, or pr oducts are more effective in clean-up operations for several oils. The se windows have been estimated utilizing oil weathering and technology performance data as tools to optimize effectiveness in marine oil spi ll response decision-making. The windows will also provide data for ac tion or no-action alternatives. Crude oils and oil products differ gre atly in physical and chemical properties, and these properties tend to change significantly during and after a spill with oil aging (weather ing). Such properties have a direct bearing on oil recovery operations , influencing the selection of response methods and technologies appli cable for clean up, including their effectiveness and capacity, which can influence the time and cost of operations and the effects on natur al resources. The changes and variations in physical and chemical prop erties over time can be modeled using data from weathering studies of specific oils. When combined with performance data for various equipme nt and materials, tested over a range of weathering stages of oils, wi ndows-of-opportunity can be estimated for spill response decision-maki ng. Under experimental conditions discussed in this paper, windows-of- opportunity have been identified and estimated for four oils (for whic h data are available) under a given set of representative environmenta l conditions. These 'generic' windows have been delineated for the gen eral categories of spill response namely: (1) dispersants, (2) in situ burning, (3) booms, (4) skimmers, (5) sorbents, and (6) oil-water sep arators. To estimate windows-of-opportunity for the above technologies (except booms), the IKU Oil Weathering Model was utilized to predict relationships-with 5 m s(-1) wind speed and seawater temperatures of 1 5 degrees C. The window-of-opportunity for the dispersant (Corexit 952 7(R)) with Alaska North Slope (ANS) oil was estimated from laboratory data to be the first 26 h. A period of 'reduced' dispersibility, was e stimated to last from 26-120 h. The oil was considered to be no longer dispersible if treated for the first time after 120 h. The most effec tive time window for dispersing Bonnie Light was 0-2 h, the time perio d of reduced dispersibility was 2-4 h, and after 4 h the oil was estim ated to be no longer dispersible. These windows-of-opportunity are bas ed on the most effective use of a dispersant estimated from laboratory dispersant effectiveness studies using fresh and weathered oils. Labo ratory dispersant effectiveness data cannot be directly utilized to pr edict dispersant performance during spill response, however, laborator y results are of value for estimating viscosity and pour point limitat ions and for guiding the selection of an appropriate product during co ntingency planning and response. In addition, the window of opportunit y for a dispersant may be lengthened if the dispersant contains an emu lsion breaking agent or multiple applications of dispersant are utiliz ed. Therefore, a long-term emulsion breaking effect may increase the e ffectiveness of a dispersant and lengthen the window-of-opportunity. T he window-of-opportunity of in situ burning (based upon time required for an oil to form an emulsion with 50% water content) was estimated t o be approximately 0-36 h for ANS oil and 0-1 h for Bonnie Light oil a fter being spilled. The estimation of windows-of-opportunity for offsh ore booms is constrained by the fact that many booms available on the market undergo submergence at speeds of less than 2 knots. The data su ggest that booms with buoyancy to weight ratios less than 8:1 may subm erge at speeds within the envelope in which they could be expected to operate. This submergence is an indication of poor wave conformance, c aused by reduction of freeboard and reserve net buoyancy within the ra nge of operation. The windows-of-opportunity for two selected skimming principles (disk and brush), were estimated using modeled oil viscosi ty data for BCF 17 and BCF 24 in combination with experimental perform ance data developed as a function of viscosity. These windows were est imated to be within 3-10 h (disk skimmer) and after 10 h (brush skimme r) for BCF 17. Whereas for BCF 24, it is within 2-3 d (disk skimmer) a nd after 3 d (brush skimmer). For sorbents, an upper viscosity limit f or an effective and practical use has in studies been found to be appr oximately 15,000 cP, which is the viscosity range of some Bunker C oil s. Using viscosity data for the relative heavy oils, BCF 17 and BCF 24 (API gravity 17 and 24), the time windows for a sorbent (polyamine fl akes) was estimated to be 0-4 and 0-10 d, respectively. With BCF 24, t he effectiveness of polyamine flakes, was reduced to 50% after 36 h, a lthough it continued to adsorb for up to 10 d. For BCF 17, the effecti veness of polyamine flakes was reduced to 50% after 12 h, although it continued to adsorb for up to 4 d. The windows-of-opportunity for seve ral centrifuged separators based upon the time period to close the den sity gap between weathered oils and seawater to less than 0.025 g ml(- 1) (which is expected to be an end-point for effective use of centrifu gal separation technology), were estimated to be 0-18 (ANS) and 0-24 h (Bonnie Light) after the spill. Utilizing the windows-of-opportunity concept, the combined information from a dynamic oil weathering model and a performance technology data base can become a decision-making to ol; identifying and defining the windows of effectiveness of different response methods and equipment under given environmental conditions. Specific research and development needs are identified as related to f urther delineation of windows-of-opportunity.