Effect of interaction between CO2 and crude oil on the evolution of interface characteristics

Abstract

CO2 flooding is now widely used as an enhanced oil recovery (EOR) technology and is also one of the most valuable CCUS processes. The interface characteristics of CO2 with crude oil and the rock matrix dynamically change during CO2 flooding. In this paper, a high temperature and high pressure visual reactor was used to observe the process of CO2 dissolution and crude oil expansion, which was followed by extracting light components with increasing pressure. A TRACKER interfacial tension meter was used to measure the dynamic changes in the CO2-crude oil interfacial tension (IFT) and the contact angle (CA) of CO2-crude oil-quartz with the pressure and temperature variations. The experimental results show that as the pressure increases, more CO2 is dissolved into the crude oil, and the volume of oil expands gradually. The saturated oil volume reaches the maximum under a certain pressure. When the pressure is further increased past this point, the extraction of the light components by CO2 becomes obvious, the volume of oil shrinks, and the heavy components are deposited. The interface characteristics are closely related to the phase interaction between CO2 and crude oil. Both the IFT of CO2-crude oil and the CA of CO2-crude oil-quartz decrease with the dissolution of CO2 as the pressure increases. As the pressure approaches the minimum miscibility pressure (MMP), the light components extraction is enhanced, and the interface of crude oil becomes extremely unstable. The IFT and the MMP increase with increasing temperature. The effect of temperature on the MMP becomes more significant when CO2 transforms to the supercritical state. This work is helpful for understanding the evolution of interface characteristics during CO2 flooding.