Influence of CO2 on asphaltene adsorption dynamics at the Oil-Gas Interface: New insights into precipitation and aggregation processes

Abstract

To investigate the effect of CO2 on the precipitation of asphaltene in oil, and verify the advantages of CO2 flooding, this work designs interfacial tension experiments and PVT system experiments to create the experimental environment under different temperature and pressure conditions that make CO2 contact with oil. The results indicate that CO2 can affect the oil morphology, and the trend of oil volume increase and decrease depends on the dynamic balance between the expansion effect and the component extraction effect of CO2 on oil. Under low pressure, the oil expansion caused by dissolved CO2 dominates the experiments, increasing the oil volume. Under high pressure, sufficient CO2 in the oil activates its component extraction effect, and the asphaltene in the oil precipitates and accumulates at the interface between the oil and CO2 due to the disruption of the component equilibrium of the system, exerting a surface activity effect, leading to a decrease in oil volume. Due to the movement of asphaltene towards the system interface and the formation of an asphaltene film during this stage, which hinders the entry of CO2 into the oil, the interfacial tension shows three linear decreasing trends with increasing pressure. This mechanism also changes the variation trend of the oil volume in CO2 during the pressure increase. Moreover, the components of the oil extracted by CO2 will be transferred to CO2, making its properties similar to oil. With the reduction of interfacial tension, this process promotes the miscibility between the two. These effects verify that CO2 can improve the fluidity and quality of oil during reservoir development, and reduce or even eliminate the adhesion work required for the working fluid to displace the oil. These conditions are conducive to improving reservoir development efficiency, reflecting the great application value of CO2 flooding.