Viscosity-Temperature Properties of Model Oil Systems Rich in Asphaltenes and Paraffins

The paper describes a comparative assessment of viscosity-temperature curves for a number of model mixtures prepared from crude oil maltenes isolated from unstable oils (with island-type asphaltenes) and stable oils (with archipelago-type asphaltenes) with the addition of 5 wt % of individual n-alkanes (C10 or C23) and/or asphaltenes (native or foreign). All the viscosity-temperature curves consist of two distinct regions, namely a lowtemperature region (10-30 degrees C) and a high-temperature region (30-50 degrees C), within which the behavior of oil systems is governed by the presence of solid paraffin crystals and the aggregation state of asphaltenes, respectively. It is assumed that, at high temperatures, the most critical factors responsible for the viscosity-temperature properties of oil systems are the asphaltene structural type (island or archipelago) and the propensity of the asphaltenes to flocculation or paraffin-asphaltene aggregation. It is further demonstrated that the flocculation of asphaltenes is accompanied by the entrapment of n-alkanes contained in the dispersion medium, and that the amounts trapped by island-type asphaltenes are higher.