Surface forces and wettability

A fundamental understanding of the wettability of rock surfaces by crude oil and brine requires a good description of the interactions between the different materials in contact. The objective of this study was to measure those interactions and to establish their implications on the observed wetting behavior. A surface forces apparatus (SFA) was used to measure the force of interaction between two molecularly smooth mica surfaces confining thin films of crude oil or brine at different conditions of pH and salinity. Modifying one or both surfaces by adsorption of polar species from the crude oil, the interaction between mica and oil in a brine environment was also measured. The measured surface forces were correlated with the results of adsorption and wettability (dynamic contact angle) experiments under the same conditions of salinity and pH, and the relative importance of the different forces observed was established. It was further established that different species in the crude oil determine the wetting behavior, and a tentative generic “wettability map” is proposed.