Evaluation of Asphaltene Hildebrand and Hansen Solubility Parameters Using Digital Oil Models with Molecular Dynamics Simulation

Abstract

The solubility parameter characterizes solubility in terms of simple numbers representing cohesive energy contribution within the molecular system and thus is considered a powerful approach for understanding highly complex systems such as asphaltenes. To obtain solubility parameters, compared with the traditional experimental method, molecular dynamics (MD) simulation provides an efficient approach and gives an explanation at the molecular level. In this study, we calculated the solubility parameters of asphaltenes using MD simulations with the digital oil model that we developed for a domestic oilfield. We have also computed the solubility parameters for more than 20 different solvents, including mixtures, to gain confidence. A new method to calculate asphaltene Hansen solubility parameters (HSPs) in solvents was proposed and implemented. This method uses a small solvent molecule as a probe. It considers different aggregation states and the potential to form hydrogen bonds in solvents, which successfully separate polar and hydrogen bonding contributions from the total cohesive energy. Six types of solvents, including heptane, toluene, isopropyl alcohol (IPA), pyridine, o-xylene, and toluene–IPA mixtures, were employed. For the toluene–IPA mixtures, different concentrations were considered. Utilizing the obtained asphaltene solubility parameters, we drew Hansen solubility sphere diagrams and estimated the solubility of asphaltenes in a solvent using the Flory–Huggins thermodynamic model, which gives results in line with expectations. Furthermore, an optimal toluene–IPA mixing solvent concentration ratio was found for asphaltenes of our target oilfield. This was achieved by tuning the polar and hydrogen bonding interaction contributions in the mixtures. Further onward, using the same method to calculate the solubility parameters for predicting asphaltene deposition risk during production, such as CO2-EOR, will be possible.