Adsorption of Crude Oil, Asphaltenes, and Resins on Calcite Surfaces: Molecular Simulation Study

Heavy oil, an important energy resource, has low extraction efficiency from reservoirs due to the presence of heavy components. Understanding their interactions with rock surfaces is essential for enhanced oil recovery (EOR). Here, we used molecular dynamics and enhanced sampling simulations to investigate the adsorption behavior of crude oil (Heptol), asphaltene, and resin molecules on calcite surfaces. The Heptol exhibits multilayer adsorption near the surface (having a contact layer, interfacial layers, and a bulk phase), with toluene dominating the contact layer. Toluene adsorbs parallel to the surface, surrounding calcium ions, while heptane occupies the leftover regions. The free-energy profiles indicate a higher adsorption preference of asphaltene than resin, favored by stronger interactions with the surface than Heptol. The key difference arises from heteroatom–surface interactions, which are attractive for asphaltene and repulsive for resin, whereas core-surface and chain-surface interactions are similar. Based on detailed analysis, we discuss the implications of our results for EOR.