Abstract
Abstract Correlations between acid and base numbers, crude oil composition and wettability for crude oil/water/quartz systems have been investigated. Twelve North Sea crude oils were characterised with respect to asphaltene content and composition of saturates, resins and aromatics by the use of thin liquid chromatography. Acid and base numbers were measured for each crude oil. The acid numbers varied from 0.02 to 2.8, while the base numbers were in the range of 0.3 to 1.6. One of the crude oils was separated into asphaltenes and deasphaltened oil, measuring acid and base number for both fractions. Based on different acid and base contents three of the oils were chosen for adhesion tests and contact angle experiments on quartz surfaces as a function of pH. These crude oils were also investigated with respect to interfacial activity. The amount of acids and bases was found to be proportional to the amount of polars (NSO and asphaltenes). The acid and base numbers were correlated, meaning that a high acid number usually corresponded to a high base number. For the fractionated oil the deasphaltened oil was found to contain approximately equal amounts of acids and bases as the original crude oil. The results from contact angle measurements show more water wet surface at higher acid number, and more oil wet behaviour at higher base number. The interfacial tension of the crude oil/brine interface increased with increasing base/acid ratio.
Published Version
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