An instrument (and corresponding method) performs AFM techniques to characterize properties of a sample of reservoir rock. The AFM instrument is configured to have a probe with a tip realized from reservoir rock that corresponds to the reservoir rock of the sample. The AFM instrument is operated to derive and store data representing adhesion forces between the tip and the sample at one or more scan locations in the presence of a number of different fluids disposed between the tip and the sample. The AFM instrument is further configured to perform computational operations that process the data representing the adhesion forces for a given scan location in order to characterize at least one property of the rock sample at the given scan location. The properties can include total surface energy of the rock sample as well as wettability of the rock sample.