Organic fluid migration in low permeability reservoirs restricted by pore structure parameters

The flow of fluids in porous media is a complex but essential study; due to the limitation of experimental methods, the research on ultra-low velocity flow of fluids has been developing slowly. This paper investigated the flow of oil in shale through laboratory tests to explore the flow characteristics of organic fluids at ultra-low velocities in ultra-low permeability porous media; the experimental results show that the flow of organic fluids in a specific porous medium at ultra-low velocity still follow Darcy's law, which is different from the previous research that believed that the ultra-low velocity flow of fluids must be non-Darcy flow. However, the flow characteristics of fluids are not static and will change with external conditions (Ambient temperature or Confining pressure). Moreover, an improved mathematical model of fluid flow based on Poiseuille's law is deduced, which can be verified well by the calculation and experimental data. The model comprehensively considers the shale stress sensitivity and the effects of the boundary layer on the fluid flow. The boundary layer is cleverly calculated through the concept of shale oil occurrence and confirmed with molecular dynamics simulation results. The correlation analysis between the critical parameters in the model and the geological parameters shows that any material composition of porous media has a specific influence on the fluid flow characteristics, especially the effect of clay minerals, that cannot be ignored. The analysis results show that when the relative content of clay minerals is about 50%, the porous medium has a better flow capacity; When the relative content of brittle minerals is between 70% and 80%, it has a better compressive ability. Simultaneously, the organic matter content index TOC has a specific inhibitory effect on fluid flow. Therefore, determining the properties of porous media and the changes in the external conditions of porous media is of great significance for engineering practice (e.g., the development of shale oil).