Discussion on the Wettability Alteration Behavior Induced by CO2-Brine-Silica Interaction and Its Effect on the Performance of Hybrid Steam-CO2 Flooding

Abstract

Hybrid steam-CO2 flooding, mature technology to enhance oil recovery, promotes the deposition of asphaltene from heavy oil and the CO2-brine-silica interaction to change the wettability of silica surface. The asphaltene deposition can promote lipophilicity of the silica surface while the CO2-brine-silica interaction can enhance its hydrophilicity. Therefore, aiming to study the wettability alteration during hybrid steam-CO2 flooding, we explore the interaction characteristics of CO2 with oil and brine on the silica surface. In this work, a series of experiments are conducted to reveal the wettability alteration of silica by the interaction of CO2 with different fluids under different conditions. The CO2-brine-silica interaction experiments and the CO2-oil-silica experiments are carried out in the temperature and pressure-resistant vessel to comprehensively acquire the silica under the influence of various fluids in the static process. In addition, based on the core flooding experiments, computerized tomography (CT) technology is applied to realistically and automatically extract the dynamic contact angle in the dynamic process. The result of contact angle from CO2-brine-silica interaction experiments shows the interaction between CO2 and brine evidently enhances the hydrophilicity of the silica surface under high temperature, and the ability of CO2 and brine to promote the increase of hydrophilicity is much greater than that in the absence of CO2. Moreover, the result of contact angle from CO2-oil-silica experiments indicates the increase of temperature and CO2 pressure makes the silica surface covered by heavy oil present the tendency of hydrophobia. The micro-CT images from core displacement experiments are automatically processed by an intelligent algorithm to extract the remaining oil distribution and display the data of dynamic contact angle. Under the influence of steam, the remaining oil mainly performs the form of membrane oil attached to the silica surface. Furthermore, the edges of the remaining oil take on an irregular shape and the contact angle reflecting hydrophobicity reach 45.2% after steam flooding. After the stage of CO2 flooding, the obvious reduction in membrane oil thickness occurs and the number of contact angles reflecting hydrophobicity decreases to 35.3%. Moreover, the oil film gradually transforms into many oil droplets on the surface under the steam and CO2, which may be conducive to the migration of heavy oil in a porous medium. Taking static and dynamic characteristics of contact angle into account under different environments, the conditions and mechanism of wettability alteration can serve as a perspective for CO2 application in pore-scale displacement.