Microscopic mechanism of enhancing shale oil recovery through CO2 2 flooding- insights from molecular dynamics simulations

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 2 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 2 flooding by conventional methods. This seriously limits the widespread application of CO2 2 flooding in shale oil development. Molecular dynamics offers a microscopic perspective to analyze the interaction between CO2 2 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 2 flooding are analyzed in detail, and the main factors (temperature, pressure, crude oil composition, CO2 2 injection amount, etc.) affecting the mechanism of shale oil displacement through CO2 2 flooding are summarized. Finally, this paper elucidates the current challenges in molecular simulation technology regarding the micro-mechanisms of CO2-enhanced 2-enhanced oil recovery. It also discusses the potential applications and future development directions for CO2-enhanced 2-enhanced shale oil recovery. Regarding CO2 2 shale oil recovery, important future directions for molecular simulation include CO2 2 composite oil recovery research, constructing composite mineral models, enhancing adsorption and dissolved shale oil recovery, and integrating quantum mechanics research methods. Molecular dynamics can accurately simulate the micro-displacement process of CO2 2 in shale pores, build a bridge between macro- and micro-displacement dynamics, and provide guidance for the widespread application of CO2-enhanced 2-enhanced shale oil recovery. This study provides a reference for the development and application of molecular simulation technology in unconventional oil and gas development.