Effects of Chemical Dispersants on Oil Physical Properties and Dispersion

New laboratory experiments were performed to measure the effects of chemical dispersants on oil physical properties and dispersion. Specifically, the aims of this study were to measure the effects of dispersant-to-oil ratio (DOR) on the viscosity of crude oils, the brine-oil interfacial tension (IFT) and the related size distributions of oil droplets formed under various mixing conditions. Arabian Medium, Alaska North Slope and South Louisiana crude oils and Corexit 9500 and Corexit 9527 chemical dispersants were used to perform the study. Results showed a monotonous linear increase of oil viscosity with DOR. The increase is higher with the less viscous oils than with the more viscous oils. With increases in DOR from 0 to 1:5, oil-dispersant mixture viscosity is approximately 20, 30 and 40 % greater than the pure crude oilsfor Arabian Medium, Alaska North Slope, and South Louisiana crude oils, respectively. Similar results were obtained with both chemical dispersants. As reported in previous studies, application of chemical dispersants reduces the interfacial tension significantly for all values of DOR examined in the current study including a very low value of 1:200. For instance, the interfacial tension of Arabian Medium crude decreases from 20 mN/m to less than 3.6 mN/m (the detection limit of the instrument) at DOR=1:200. The results also show that an optimum DOR exists at which the IFT reduction reaches a maximum value. At this optimum DOR, the effectiveness of the chemical dispersant is at a maximum. The consequent effects of the observed IFT reductions on the resulting size distribution of oil droplets was studied using existing theories and size measurements using UV Epi-fluorescence microscopy.