Study of the precipitation trend of asphaltenes and waxes in crude oil using computational chemistry and statistical thermodynamics methods

Abstract

Asphaltenes aggregation and waxes in petroleum were simulated considering five molecular structures containing functional groups: asphaltenes, resins, and non-polar hydrocarbons in a heavy oil crude. The properties of molecules were calculated using the density functional theory. The van der Waals constants associated with the pairwise interactions and the Hamaker constants for the dispersed phase (formed by asphaltenes and waxes) and the dispersion medium (created by non-polar hydrocarbons) were estimated. Sparse pass size as a function of its composition is calculated using Qyle groups and the Young–Laplace equation. We also assessed the potential colloidal pair corresponding to the interactions between the asphaltene and resin aggregates for different dispersion media, the attractive energies between the asphaltene molecules (−60 10–20 J ≈ ) are more than twice as high as the attractive energies concerning the rest of the molecules present ( × -30–10] 10–20 ≈ × J). It is predicted that attraction energy between the aggregates decreases with the increase of the presence of resin in the dispersed phase, This is explained by the fact that the increase in the concentration n of resin can lead to a decrease in the relative size d of the aggregates by up to 90 % (for n = 0.1, d = 0.1 and for n = 0.9, d = 0.1). This decrease in aggregate size is manifested in a theoretically calculated effective viscosity reduction of up to 50 %.