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  2.3  Bifurcated Correlations as a concequence of an apparent BI-FRACTIONAL Composition of Asphaltenes 

Publications on correlations among various properties of crude oils reveal that the amount of asphaltene is a significant variable in all cases. Currently, "asphaltenes" are defined merely as a solubility class. In spite of a diversity of physico-chemical parameters of various "asphaltene" molecules, it is commonly assumed that "asphaltenes" may be characterised by some general properties (more precisely, by unimodal distributions of these properties).

   We have performed a detailed analysis of databases for more than 390 world’s recovered (dead) crude oils. For various oil's properties the analysis revealed a presence of BIFURCATED correlations with asphaltene content.  The nature of these bifurcations was discussed on the basis of our earlier experiments on molecular and colloidal asphaltenes in fluid media.
    The main conclusion - natural "asphaltenes" are of two distinctly different types (there are bimodal distributions of "asphaltene" properties).  The first type has a higher propensity to self-association, higher heteroatom content, higher polarity and a significantly lower solubility. E.g., in toluene, its solubility is below 100 mg/l, while for the other type of "asphaltenes" a solubility limit is larger by almost three orders of magnitude (60 g/l). It should be noted, however, that with respect to some properties (e.g. metal contents) two types of asphaltenes apparently are

   Finally, BIFURCATED asphaltene-related  correlations in recovered crude oils may be attributed to a total selective loss (in course of evolution/migration of oils) of the low-soluble (polar) type of natural asphaltenes ("geochromatography" effects).     .


ABOVE - Bifurcated correlations with respect to current asphaltene content in recovered crude oils.
BELOW - A single universial correlation obtained in case of a total selective loss (in course of evolution and migration of oils) of one of the two fractions of natural asphaltenes.


Asphaltenes, selectively lost in course of migration, possess a higher content of sulphur.

Asphaltenes, selectively lost in course of migration, possess a higher polarity.


Two fractions of asphaltenes are indistinguishable with respect to the content of metals.

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      Last Update : 12.04.2005