The crude oil adsorption on model mineral surfaces such as mica and calcite has been investigated
using the atomic force microscopy technique to determine the nanoscale characteristics of crude
oil particles such as asphaltenes. In order to proceed with studying more complex surfaces, such
as reservoir rocks, one needs to be able to distinguish the features of the rocks from those of crude
oil particles. Crude oil is composed of four different fractions known as SARA fractions of crude
oil. The images obtained from AFM showed that the asphaltenes of crude oil in fact do adsorb
onto the mica discs, and the asphaltene aggregates tend to form agglomerates. Additionally, it
was found that different crude oils form agglomerates with different features, and the adhesivity
and stiffness differ from crude to crude. On a calcite surface, which is positively charged, crude
oil formed a film when the surface was submerged into crude oil and aged at a temperature of
70°C and pressures above 10 bar. This proved that the surface charge of the surface, which
crude oil’s aromatic compounds come into contact with, plays a key role in the manner in which
crude oil will wet that surface in the absence of any other compounds, such as water. Once
these patterns were established, in order to further enhance knowledge in this field, Ketton
rocks were flushed with brine and imaged in order to establish whether water films could be
imaged with AFM or not, and indeed, this was a success, and water films were successfully
detected. Then came the ultimate goal of this project, which is to determine whether crude oil’s
aromatic fractions, such as asphaltenes and resins, will wet the originally water-wet rock surface
and alter the wettability of the rock’s surface in favour of oil.