Asphaltenes in heavy crude oil: Designation, precipitation, solutions, and effects on viscosity

The results of the evaluation of asphaltene content in heavy crude oil depend on the solvent chosen; and the products obtained at this evaluation have varying effects on oil viscosity. In the experiments performed to separate compounds that might be assigned conditionally to the group of asphaltenes, not only standard solvents such as pentane and hexane but also diethyl and diisopropyl ethers as well as hexamethyldisiloxane were employed. The chemical composition of asphaltenes (as estimated using the IR method) depends on the precipitant used. The quantity of precipitated asphaltenes is directly correlated with the energy of the intermolecular interaction of the solvent. In this study, the effects of different “asphaltenes” on oil properties were evaluated by measuring the rheology of the solutions in tetralin at a wide range of temperatures. These solutions demonstrate very different properties (from Newtonian fluid to gel) depending on the concentration. Viscosity depends on the nature of the solvent used to precipitate asphaltenes. Using diethyl ether yields the smallest quantity of asphaltenes but they creates the most viscous solutions. The removal of asphaltenes leads to a significant decrease in heavy oil viscosity. Heavy oil viscosity can be decreased by 2–3 orders. The intensity of the effect is determined by the solvent's solubility parameter.