The physicochemical mechanism of formation of microstructural wettability in oil and gas reservoirs is experimentally justified. It is shown that the mechanism of microstructural wettability formation is associated with the formation of mosaic hydrophobic areas on the interstitial surface of the reservoir rocks. It was found that hydrophobic areas are formed as a result of competition of adsorption processes between aromatic and aliphatic structures. For example, the relationship between the hydrophobization index (ratio of the hydrophobic pore surface to total pore surface) and adsorbed oil composition were identified with core samples of carbonate rocks of the Karachaganak oil and gas condensate field (Karachaganak, Kazakhstan) and Astrakhan gas condensate field (South-Western part of Precaspian basin, Russia). The spectral coefficients characterizing the relative contribution of certain hydrocarbons to the composition adsorbed oil composition were determined using infrared spectroscopy. The dependences of microstructural wettability on the spectral coefficients are experimentally established. It is shown that the composition of adsorbed oil has a multidirectional impact on the microstructural wettability. The presence of aromatic, oxidized and blackened structures increases the hydrophobization index, while presence of aliphatic and branched structures reduces it. The closest relationship was found of microstructural wettability with the spectral coefficient that characterizes the presence of aromatic structures in the adsorbed oil.
