Quantitative Analysis of Wettability and Its Transition Mechanism in Carbonate Rocks Based on Surface Energy Characterization

Wettability significantly influences crude oil occurrence within reservoirs and hydrocarbon recovery efficiency. Carbonate rock wettability undergoes substantial alteration under elevated temperatures or asphalt adsorption. To quantitatively assess the impacts of temperature and asphalt on carbonate wettability and analyze its transformation mechanisms, inverse gas chromatography was employed to measure surface energy of Ordovician carbonate samples from Tahe Oilfield across 30-130 °C. With increasing temperature, the nonpolar surface energy of carbonate rocks first decreases and then increases, accompanied by enhanced basic component. Utilizing Young's equation and Van Oss theory, theoretical values of interfacial tensions and water contact angles in rock-oil-water systems were calculated based on surface energy components of rock, petroleum, and water, enabling quantitative wettability evaluation. Results demonstrate strengthened water-wetting characteristics with temperature elevation, primarily governed by increased acidic and basic components of carbonate surface energy. More polar carbonate samples exhibit superior hydrophilicity compared to less polar counterparts at equivalent temperatures. The oil-wetting enhancement mechanism through asphalt adsorption arises from ultralow asphalt-carbonate interfacial tension at ambient conditions, facilitating spontaneous asphalt adsorption. Asphalt-coated surfaces dramatically increase water contact angles in light oil-water systems, intensifying oil-wetting behavior. Optimal recovery temperatures range in 60-100 °C for fractured carbonate reservoirs containing light oil and in 100-110 °C for asphalt-rich reservoirs.