Rate of weathering of Cold Lake Blend diluted bitumen at different water temperatures taking into consideration uncontrolled environmental factors

Abstract

The rate of weathering of Cold Lake Blend diluted bitumen in floating microcosms in an experimental flume tank was monitored over time (0, 6, 24, 48, 72, 96, and 168 hours) under controlled temperature conditions (4, 10, 15 and 25 °C). At all temperatures, the most rapid change in the physical properties (density and viscosity) and chemical composition (saturates and aromatics) of the oil occurred within the first 48 hours. Correlation analyses showed that seawater temperature and the uncontrolled factors (wind speed and air temperature) were significantly correlated on the rate of change in the physical properties of the oil. Gas chromatography mass/spectrometry analyses of the composite samples of weathered oil showed similar results for changes in its chemical composition. At 168 hours of weathering, the relative decrease of the saturates (C₁₀ to C₁₇ normalized to 17α, 21β-hopane) increased with the temperature. The percent decrease was 16, 24, 42, and 57 at 4, 10, 15 and 25 °C respectively. A similar trend was observed for the aromatics. From these, the percent decrease of naphthalene and its alkylated homologues was largest at 15 °C and above. These changes in the chemical composition and physical properties of the oil most likely resulted from the loss of the diluent. The data from this study on the weathering of diluted bitumen over a range of seawater temperatures, is the first of its kind, and thus may be used in predictive models to improve recommendations for responding and/or to improve contingency planning to oil spills.