Impact of below-freezing air temperatures on the formation and stability of seawater-crude oil emulsion

The formation of 'seawater-in-oil' emulsions reduces the effectiveness of current oil spill response operations such as the physical recovery of oil with skimmers, or oil dispersion with chemical dispersants, due to increases in volume and viscosity. This becomes even more acute in cold regions because of the potential for below-freezing temperatures and floating ice. Low temperatures increase oil viscosity and can freeze entrained water droplets, potentially inhibiting the formation of new emulsions while stabilizing any that have already formed. Existing works on emulsion behavior at near-freezing temperatures may have underestimated the impact of below-freezing air temperatures, common in polar regions, on the formation and stability of seawater-in-oil emulsion. To address this issue, we investigated the behavior of emulsions exposed to below-freezing air temperatures (-20 °C), studying oils with different asphaltene contents. Higher asphaltene content (18 wt%) was correlated with increased emulsion stability, but emulsions that experienced freezing air temperatures were more prone to break during thawing. After -20 °C treatment, Hibernia emulsions lost >50 % of their entrained water, while Alaska North Slope emulsions lost >25 %. Samples kept at 20 °C lost far less. Emulsions exposed to significantly sub-zero temperatures in Polar regions are thus likely to break when they thaw, which will impact oil spill response.