A review on shale oil and gas characteristics and molecular dynamics simulation for the fluid behavior in shale pore

Shale oil and gas primarily exist in nanoscale pore-fracture networks. Thus, it is essential to clarify the flow behavior of hydrocarbon in confined nanopores. This paper summarizes shale oil and gas distribution and exploration status, reviews the microscopic pore structure characterizing methods and methods of investigating fluid behavior in micro-nanopores. Because the multiphase fluid experiment in nanopores requires sufficiently high precision instruments, and the temperature and pressure of the experiment are difficult to indicate the actual formation conditions, molecular dynamics simulation is the inevitable research technique for investigating fluid behavior in shale nanopores. Therefore, the most recent developments and conclusions of molecular dynamics simulation for adsorption, diffusion and flow (displacement) in shale reservoirs are introduced. The simulated substrates include organic matter (graphene, CNT and kerogen), inorganic matter (quartz, calcite, clay, etc.), and mixed matter. The simulated oil and gas component include pure composition and multi-composition. In addition, water, carbon dioxide, supercritical carbon dioxide, and nitrogen are also utilized in the simulation as the displacement or coexistence phases. The temperature, pressure, slit width, water content, oil content and surface characteristics determine the distribution and transportation of fluid in the pore, and consequently impact the production rate. In addition, this paper also discusses the mechanisms of enhanced oil and gas recovery in shale reservoirs, and summarizes the future development of the molecular dynamics simulation of shale oil and gas.