Review on Changes in Shale Oil Property During CO2 Injection

The influence of supercritical CO2 on the properties of petroleum has become the focus of academic and industrial attention internationally. CO2 has been shown in laboratory studies and in field applications of shale oil to be an effective oil displacement agent. In this paper, the research progress of the interaction between CO2 and crude oil is investigated from three perspectives: (i) the research methods of the interaction experiment between CO2 and crude oil; (ii) the influence of CO2 on oil property and the primary controlling factors; and (iii) the cause, influence, and harm of CO2-induced asphaltene precipitation. Our current knowledge on this topic is as follows: (1) Physical simulation can investigate the effects of various variables on CO2 displacement, which is in situ and intuitive. Numerical simulation can investigate the displacement principle at the microscopic molecular level and also scale up the results of physical simulation to the macroscopic scale of oilfield production to explore the long-term large-scale injection rules; (2) after entering the formation, CO2 dissolves in crude oil, expands the volume of crude oil, reduces the viscosity, improves the oil-water mobility ratio, reduces the oil-water interfacial tension, and extracts light hydrocarbons to form a miscible displacement zone; (3) after CO2 is injected into the formation and dissolves in crude oil, it occupies the surface space of asphaltenes and causes asphaltenes to precipitate. Under the combined influence of internal and external factors, the precipitation of asphaltenes has a significant impact on the physical properties of the reservoir. Clarifying the influencing factors of CO2 on the property of crude oil has reference significance for understanding the reaction characteristics between supercritical CO2 and formation fluids, providing a theoretical basis for CO2 injection enhanced oil recovery technology, and has reference value for carbon storage research.