Molecular dynamics simulation has emerged as a powerful tool to shed light on the fundamental mechanisms that govern fluid behavior across multiple phases, such as gas, liquid and solid, at the molecular-scale. In shale reservoirs, understanding nanoscale phenomena such as microscopic friction, oil-gas interactions during CO2 huff-n-puff processes, and the influence of co-solvents, is crucial for enhanced oil recovery and informing strategies for CO2 geological sequestration in shale. This paper explores the unique role of molecular dynamics simulations in revealing the microscopic mechanisms of fluid transport and enhanced recovery during CO2 injection, with particular attention to the effects of hydration film, CO2 affected areas and co-solvents. The regulatory mechanism of hydration films on the friction behavior of montmorillonite provides new insights into interfacial mechanics, with implications for the mobility of confined fluids. In tight reservoir systems, the microscopic oil recovery mechanisms of CO2 under varying sweep conditions water film thicknesses highlight the complexity of fluid displacement at the nanoscale. Furthermore, the co-injection of CO2 with selected co-solvents is shown to enhance both oil mobilization and carbon storage efficiency within shale nanopores, offering a promising pathway to improve recovery outcomes under diverse reservoir conditions. By providing a molecular-level understanding of these critical processes, this work lays the groundwork for bridging atomistic insights with field-scale applications for unconventional resources development. Document Type: Perspective Cited as: Bao, J., Du, J., Zhan, S., Wang, L., Luo, Y. A molecular perspective on the microscopic mechanisms of CO2 injection and water films in fluid transport and enhanced oil recovery. Advances in Geo-Energy Research, 2025, 16(3): 288-292. https://doi.org/10.46690/ager.2025.06.08

It is difficult to investigate the formation process and occurrence states of water in multi-type reservoirs, due to the strong heterogeneity and complex microstructure of the fracture–cavity carbonate gas reservoirs. To date, there is no systematic study on the occurrence characteristics of multi-type formation water, especially through visual observation experiments. In this paper, a new creation method for visual micromodels based on CT scan images and microelectronic photolithography techniques was described. Subsequently, a gas–drive–water visual experiment was conducted to intuitively study the formation mechanism and the occurrence states of formation water. Then, the ImageJ gray analysis method was utilized to quantitatively investigate the gas-water saturation and the proportion of residual water film. Finally, the occurrence characteristics of formation water and its effects on gas seepage flow were comprehensively analyzed. Visual experimental results showed that: the migration processes of natural gas in different types of reservoirs are different; the water in multiple media consists of native movable water and residual water, and residual water is composed of secondary movable water and irreducible water; the residual water mainly occurs in different locations of different reservoirs with the forms of “water film”, “water mass”, “water column” and “water droplets”; the main influencing factors are capillary force, surface tension, displacement pressure and channel connectivity. Quantitative results reflect that the saturation of movable water and residual water are the parameters related directly to reservoir physical properties, pore structure and displacement pressure—the smaller the size of flow channel, the larger the space occupied by water film; the thickness proportion of water film is increasing exponentially with the channel size; the thickness proportion of water film decreases as the increase of displacement pressure; the thickness proportion of water film is essentially constant when the displacement pressure increases to a certain extent. The conducted visual investigation not only improves our intuitive understanding of the occurrence characteristics of formation water, but also provides a theoretical basis for the efficient development of fracture-cavity gas reservoirs.