Role of Evaporation in Degrading the "Oil Lakes"

Problem statement: Oil Spills are degraded by aerobic bacteria, water washing, evaporation and oxidation. In the absence of water the first two of these processes cannot operate. This is the situation in the low rainfall environment of the Kuwaiti desert where oil lakes still persist 20 years after the initial spills. The oils contain longer chain n-alkanes but have lost light ends and evaporation appears to be the dominant degradation mechanism. Approach: We have simulated evaporation of Kuwaiti oil (from Burgan field) at temperatures from 20-50°C and at various air flow rates. Results: Compositional changes monitored by gas chromatography show losses of volatile components (<C8), including alkanes, aromatics and naphthenes. Normal alkanes are lost more rapidly than other hydrocarbon types with the same carbon numbers. Conclusion: Evaporation increases viscosity and density leading to compositional stratification. It seems likely that a devolatilized "skin" forms, protecting the underlying oil and decreasing the rate of evaporation. Oils degraded by evaporation show final compositions similar to those observed in the residual oil lakes.