Effect of Average Molecular Parameters of Asphaltenes on the Rheological Properties of Crude Oils from Colorado Oil Field

In our previous articles (Energy & Fuels 2017, 31, 133–139 and Energy & Fuels 2017, 31, 8997–9005), it was presented that the asphaltenes of the Colorado field have different chemical structures, and these change the properties of crystallization of the paraffins. In this paper, we present a new way to understand the effects of the chemical structure of the asphaltenes on crude oil rheology, which includes correlating the average molecular parameters (AMPs) and the concentration of the asphaltenes with rheological properties using chemometric methods such as the partial least squares method. The asphaltenes were separated from six crude oil samples (average °API of 38) and were characterized using nuclear magnetic resonance to determine their main molecular parameters. Rheological properties including viscosity, yield stress, and gel temperature were experimentally determined for each of the crude oil samples and their respective maltenes. The results of a multivariate analysis show that the AMPs of the asphaltenes that cause the greatest effects are the ratio of peripheral aromatic carbons to aromatic carbons (Cp/Car) and pericondensed aromatic carbons (Caaa), which increase the gel temperature among maltenes and crude oils. The concentration of the asphaltenes (Coasf) contributes to decreasing this property. An increase in the yield stress is mainly caused by the aliphatic chains of the asphaltenes (n) and the molecular weight (M w), whereas Coasf causes decrease on the yield stress. Finally, the change in viscosity at 20 °C is increased by Cp/Car and is decreased by Coasf and paraffinic carbons (Cs).