Effect of biodegradation and water washing on oil properties

Abstract

Bulk and molecular properties of oils extracted from various oil sands were examined to show the effect of biodegradation and water washing on oil quality. Our results indicate that the total ion current (TIC) fragmentograms of all the studied oils show the presence of significant unresolved complex mixture (UCM) components, which is a common characteristic of oils that have undergone biodegradation. All the studied oils are also enriched in the polar fractions (asphaltene + resin) and depleted in the saturate oil fractions consistent with oils that have undergone biodegradation. The studied oils are also acidic, having total acid numbers (TAN) > ~0.5 mgKOH/goil. Such high TAN values have serious negative impact on the economic value of the oils, as high oil acidity is known to cause production and downstream handling problems such as corrosion and the formation of emulsions. This study also demonstrates that geological and geochemical processes that appear to give rise to a high concentration of sulfur in oils, and to oil acidity (typically measured as TAN), are those that favour biodegradation. Water washing is observed to occur simultaneously with biodegradation in all the studied oils. Vital roles played by water in petroleum biodegradation include acting as a reactant in biodegradation processes and carrying nutrients needed for life.