Research progress of CO2 flooding in tight sandstone reservoirs based on molecular dynamics method

With the increasing number of tight sandstone reservoir CO2-EOR projects, it is in urgent need to study the interactive mechanisms of CO2 and tight sandstone reservoir fluids in porous media. In laboratory experiments, however, it is difficult to observe the dynamic processes of CO2 and fluids in pore channels, while molecular dynamics simulation can make up for the shortcomings of traditional experiments and numerical methods. Focusing on the two major points of molecular dynamics simulation in the research of CO2-EOR, i.e., interface behaviors and flow behaviors in confined spaces, this paper systematically reviews the research results related to interface behaviors from six aspects including extraction, swelling, viscosity reduction, interfacial tension reduction, minimum miscible pressure and wettability. And then combined with the previous research results of the flow behaviors of CO2 and tight sandstone reservoir fluids in confined spaces, the key scientific issues of molecular dynamics in the research of tight sandstone reservoir CO2-EOR are pointed out. First, molecular dynamics can visualize the extraction process of medium-light hydrocarbon compositions from crude oil by CO2. It is suggested to analyze CO2's extraction capacity considering the actual crude oil compositions, so as to determine the extraction order and efficiency of each composition by CO2. Second, the research results related to the swelling and viscosity reduction effect of CO2 molecule on crude oil are mostly involved in the simple crude oil composition system. It is suggested to systematically discuss the swelling and viscosity reduction effect of CO2 under high temperature and high pressure based on the crude oil compositions of actual reservoirs. Third, the interfacial tension between CO2 and oil-water two phases is studied mostly in gas phase, and it is necessary to further study the interface behaviors in nano-scale confined spaces. Fourth, as for the wettability of formation water on the surface of pore wall, the influential mechanisms of synergistic effects between different factors on wettability have not been figured out. In conclusion, as quantum mechanics is studied further and the calculation capacity gets stronger, this method can be used for the calculation of complex systems in a larger scale, and the researches on CO2-EOR mechanisms in oil reservoirs and shale oil and gas reservoirs based on it will achieve great breakthroughs. © 2024 Natural Gas Industry Journal Agency. All rights reserved.