Publications on correlations among various properties of crude oils reveal that the amount of asphaltene is a significant variable in all cases. In particular, it has been repeatedly stated that there are positive correlations between density and viscosity of crude oils and asphaltene concentration. Moreover, it is widely held that each of these correlations may be represented by a single analytical function (a single curve), which may be employed in various “universal” models of petroleum.

    We have performed a detailed analysis of databases for more than 390 world’s recovered (dead) crude oils. For densities and viscosities of oils the analysis revealed a definite absence of frequently quoted single-function correlations with asphaltene content and the existence of two distinct types of world’s crude oils as classified with respect to their asphaltene-based correlations.
   

       

Bifurcated correlation of viscosity with asphaltene content for world's crude oils.
(Smoothened general trends)