The adsorption and deposition of asphaltene and resin from crude oil on reservoir rocks is a major factor in wettability changes. The microstructure of asphaltene adsorption from 600mg/L asphaltene simulated oil on the silica sand is visualized clearly through scanning electron microscope(SEM). The results show that silica immersed in the asphaltene simulated oil for 70 days adsorb asphaltene by adsorption film with various thickness. The silica sands in an ascending order of asphaltene adsorption film thickness are the silica sands pretreated by 12% NaOH solution, 10% HCl solution, and 10% HCl plus 12% NaOH solution successively. The differences of hydroxy silanol group states and the electric characteristics of the silica sand surface pretreated by three different approaches lead to the distinctions of asphaltene adsorption. Furthermore, there always exist some sand grains and/or specific parts of a sand grain with no asphaltene no matter which method is adopted to pretreat the silica sands, which indicates the adsorption of asphaltene and resin on the silica sand is heterogeneous. In the actual oil reservoir, reservoir rock is presumably mixed wettability.
