Influence of the Component Composition of Adsorbed Oil on the Microstructural Wettability of Hydrocarbon Reservoirs

Abstract

The physicochemical mechanism of the development of microstructural wettability in oil and gas reservoirs is experimentally justified. It is shown that this mechanism is associated with the formation of mosaic hydrophobic areas on the interstitial surface of the reservoir rocks. It was revealed that hydrophobic areas are formed due to the competition of adsorption processes between aromatic and aliphatic structures. For example, the relationships between the hydrophobization index (the ratio of the hydrophobic interstitial surface to the total pore surface) and adsorbed oil composition were identified by studying core samples of carbonate rocks from the Karachaganak oil and gas condensate field (Kazakhstan) and the Astrakhan gas condensate field (southwestern part of the pre-Caspian Basin, Russia). The spectral coefficients characterizing the relative contribution of certain hydrocarbons to the 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 effect on microstructural wettability. The presence of aromatic, oxidized, and sulfurized structures increases the hydrophobization index, whereas the presence of aliphatic and branched structures leads to its reduction. The closest relationship was noted between the microstructural wettability and the spectral coefficient that characterizes the presence of aromatic structures in the adsorbed oil.