Crude oil and asphaltene characterization for prediction of wetting alteration

Abstract

Measures of a crude oil's polar functionality and asphaltene stability are key to predicting its wetting behavior. No publicly available data sources and few proprietary databases include all of the information necessary to characterize a crude oil with respect to its interactions with solid surfaces in the presence of an aqueous phase. At a minimum, this information includes both acid and base numbers, which are related to polar and ionic interactions between oil components and charged mineral surfaces, and refractive indeces (RI) of both the oil and oil mixtures at the onset of asphaltene flocculation, which is related to asphaltene stability. Data accumulated thus far illustrate a linear relationship between API gravity and refractive index that can be used to estimate refractive index from existing data. Acid and base numbers for many different crude oil samples show little evidence of correlation between the two, thus both numbers are needed for prediction of wetting alteration. Measurements of refractive index at the onset of precipitation with n-heptane are used to characterize asphaltene stability. Extensive data for seven crude oils are presented to illustrate how asphaltene stability can be predicted over a wide range of conditions from the n-heptane onsets.