Wettability and morphology of mica surfaces after exposure to crude oil

Reservoir wettability is determined by interactions between crude oil and mineral surfaces, mediated by an aqueous phase. Contact angles between immiscible fluids have long been used as probes to assess the effective wetting condition of surfaces after exposure to brine and oil, but there is a limit to the amount of information that can be deduced from contact angles in such nonideal conditions. s study, atomic force microscopy (AFM) has been used to observe mica surfaces treated with a series of crude oils that produce a wide range of wetting conditions—water-advancing contact angles on these surfaces vary from water-wet to oil-wet. In the most water-wet case, the only adsorbed features appear to be small, water-wet particles that are probably inorganic. All of the other oils deposited organic coatings, with varying thickness, morphology, and durability. Weakly water-wet systems exhibited many surface features, but the waitings tended to be unstable and to detach from the surface, especially during AFM scanning in water. The most oil-wet systems exhibited thick, stable organic coatings that were not disturbed by AFM scanning.