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).
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 indistinguishable.
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). .