An AFM study of the morphological features that affect wetting at crude oil–water–mica interfaces

Crude oil is typically produced from subsurface rock formations that consist of extensive pore networks filled with oil, water, and gas phases. Such systems exhibit significant heterogeneities in wetting properties due in part to mineralogy, but oil composition, connate water chemistry, and saturation history of the pores can be even more influential. Crude oils contain many polar compounds that can adsorb on mineral surfaces, changing their effective wetting. Most of what is known about crude oil/brine/rock interactions, however, has been inferred from contact angle measurements. There is little direct information about the complex morphology of adsorbed and deposited materials that alter wettability. Atomic force microscopy—optimized for the study of soft material in a variety of fluid environments—is used in this study to observe micron- and nanometer-scale changes in topography on mica surfaces before and after exposure to crude oil. Density of coverage and film structure are related to exposure time and crude oil chemistry. Asphaltene aggregates and other features that form a continuous surface film are resolved with this technique that, coupled with contact angle measurements, provides a powerful method for examining the mechanisms that control wettability in crude oil/brine/rock systems.