Rheology of Reconstituted Crude Oils: Artifacts and Asphaltenes

The properties of asphaltenes present in crude oils remain subjects of debate in the literature. In this work, the complex and zero shear viscosities of reconstituted samples prepared by mixing chemically separated pentane asphaltenes and maltenes were obtained. The samples were of four different types, namely: Athabasca asphaltene + Athabasca maltene (reconstituted Athabasca bitumen), Maya asphaltene + Maya maltene (reconstituted Maya crude), as well as cross mixtures comprising Athabasca asphaltene + Maya maltene, and Maya asphaltene + Athabasca maltene. The zero shear viscosities of these samples are compared with one another, with the zero shear viscosities of asphaltene + pure diluent binary mixtures, and with zero shear viscosities of nanofiltered Athabasca bitumen and Maya crude oil samples reported previously. The Maya and Athabasca asphaltene properties in reconstituted samples are shown to differ from one another and from those in nanofiltered samples. However, the large temperature and composition variation of the relative viscosity of such mixtures is attributed primarily to redistribution of residual pentane from the maltenes to the asphaltenes on reconstitution and only secondarily to properties of the chemically separated asphaltenes themselves. The physics and chemistry of asphaltene behavior and of the differences arising from separation methods and diluent environments are not resolved in the present work and remain subjects for ongoing investigation.