Microscopic mechanism of enhancing shale oil recovery through CO2 flooding- insights from molecular dynamics simulations

•Shale oil reservoirs have micro-nano pores and complex fluid occurrence characteristics. They are also rich in organic matter. When shale oil is adsorbed by organic carbon, it exists in both adsorbed and dissolved states. When the adsorption capacity of organic carbon reaches saturation, shale oil exists in the free state.•Molecular dynamics simulation studies have shown that the micro mechanisms of enhanced shale oil recovery through CO2 flooding mainly include crude oil swelling, crude oil viscosity reduction, CO2 diffusion, CO2 extraction, CO2 crude oil mixing, and adsorption and competitive adsorption, among others.•Molecular dynamics simulation of enhanced shale oil recovery through CO2 flooding will primarily focus on CO2 composite oil recovery, constructing composite mineral models, enhancing adsorption and dissolved shale oil recovery, and integrating with quantum mechanics research methods. Shale oil reserves are abundant worldwide and are a primary focus for future oil and gas development. Shale reservoirs are dense, highly heterogeneous, and have a low oil recovery degree. CO2 flooding can achieve the efficient development of shale oil, but the development of micro- and nano-pores in shale oil reservoirs and the complexity of fluid occurrence make it difficult to analyze the micro-mechanisms governing the enhanced recovery of shale oil through macroscopic CO2 flooding by conventional methods. This seriously limits the widespread application of CO2 flooding in shale oil development. Molecular dynamics offers a microscopic perspective to analyze the interaction between CO2 molecules and crude oil molecules in various states of occurrence, including their interaction with shale pore walls. This approach has become a crucial method for studying reservoir development. In this paper, first, the molecular dynamics simulation methods are summarized, including details on basic principles, force fields, ensemble theory, boundary conditions, simulation process, and molecular simulation software. Second, the characteristics of shale oil reservoirs are elucidated from the perspectives of shale reservoir properties, kerogen type, and occurrence status. The micro-mechanisms (swelling, diffusion, viscosity reduction, extraction, mixing, adsorption, and competitive adsorption) of the displacement of shale oil through CO2 flooding are analyzed in detail, and the main factors (temperature, pressure, crude oil composition, CO2 injection amount, etc.) affecting the