Molecular insights into CO2 enhanced oil recovery and CO2 storage in quartz nanopores

B Li and HG Sui and DS Wang and YD Wang and FY Zhang and J Yao, GEOENERGY SCIENCE AND ENGINEERING, 246, 213640 (2025).

DOI: 10.1016/j.geoen.2024.213640

Injecting CO2 into shale oil formations significantly enhances oil recovery, and also provides a practical application scenario for carbon utilization and storage. Gaining a profound understanding of the microscopic mechanism of CO2-enhanced oil recovery in achieving optimal exploitation and ensuring the sustainable development of shale oil resources is crucial. In this paper, the static properties of shale hydrocarbons and the underlying mechanism of CO2-enhanced shale oil recovery within quartz nanopores are investigated by molecular dynamics simulation. Multilayer adsorption is observed within the quartz nanopores, and the density distribution of oil exhibits symmetry about the central plane (x = 0) of the two basal surfaces. For flooding behavior, CO2 preferentially replaces the oil molecules in the adsorbed phase rather than oil in the bulk phase, attributed to the robust interaction between CO2 and the quartz surface. Large pressure difference improves the miscibility of gas and hydrocarbon and promotes the oil recovery efficiency. Conversely, high temperature improves oil recovery efficiency but decreases the miscibility rate. The effect of quartz slit aperture for CO2 storage is researched. The average density and capture rate of CO2 increase with the decline of pore width. The density of CO2 is 0.86 g/cm3 and the capture rate is 45% in 5 nm-width nanopores and increases to 0.92 g/cm3 and 100%, respectively, in 1 nm- width nanopores, indicating that small pore sizes possess superior CO2 stable storage potential. This study unveils the behavior of hydrocarbon and CO2 storage in shale formations, as well as the mechanism of CO2-enhanced crude oil recovery. These findings have significant implications for enhancing crude oil recovery rates and for clarifying the utilization and storage of CO2 within shale formations.

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