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The Effects of Photo-Oxidation, Wave Energy, and Crude Oil Properties on the Microstructure and Viscosity of Water-in-Oil Emulsions
DescriptionOil slicks in the open ocean are emulsified by the periodic shear of breaking waves. The resulting water-in-oil emulsions contain up to 80% water, increasing pollutant volumes by up to 5 times and viscosity by up to three orders of magnitude compared to the original crude oil. Simultaneously, photo-oxidation significantly affects crude oil composition, influencing the emulsification process. Little information exists on how microscopic structure, viscosity, and viscoelastic properties change over time during emulsification and photo-oxidation. This study experimentally investigates the impact of wave energy and photo-oxidation on the emulsification process of artificial seawater in crude oil. It examines the time evolution of bulk viscosity, viscoelastic properties, and microscopic morphology of emulsions produced by breaking waves impinging on 2 mm thick oil slicks. Crude oil slicks from Hibernia, Alaskan North Slope (ANS), and Cold Lake are emulsified over 12 days by plunging breaking waves with a period of 40 seconds. Fluorescent microscopy is used to assess the droplet size and spatial distributions of emulsion samples that are collected daily, and rheology is used to evaluate the shear viscosity and viscoelastic properties of the emulsions. Results for light oils demonstrate that ANS emulsifies water faster than Hibernia oil, leading to higher water droplet concentration and a more interconnected droplet structure at earlier times. As a result, during the initial days of emulsification, the (non-Newtonian) viscosity of the ANS-based emulsion is at least three times greater than that of Hibernia. During a 12-day period, these light oils emulsify between 40 to 50% water by volume. Cold Lake, a diluted bitumen, emulsifies up to 40% water by volume and primarily consists of sub-micron droplets that do not form a lattice. As a result, for light oils, the storage modulus predominates, i.e., the material is more elastic than viscous, demonstrating the importance of the droplet structure in the emulsion. In contrast, for heavy oils, the loss modulus is higher, i.e., the material is more viscous than elastic. Photo-oxidation, which has only been tested for Hibernia oil, causes faster water emulsification, accelerated formation of droplet clusters, smaller characteristic droplet sizes, and a higher dominance of the storage modulus compared to those of the original oil. These trends are consistent with our previously determined Ohnesorge number-based empirical relationships between the emulsion morphology and its viscosity.
Event Type
Paper
TimeWednesday, May 15th10:20am - 10:40am CDT
Location288-290
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