Multicomponent inhomogeneous fluid transport in nanoporous media

The modified equation of state (EOS) based on critical parameter shift is widely used in continuum-scale transport modeling in nanoporous media to incorporate the confinement effects. However, it fails to account for fluid-wall interactions. In this work, the multicomponent fluid transport in nanoporous media is simulated by considering inhomogeneous fluid thermodynamics and transport properties based on pore-scale density distribution. The multicomponent simplified local density (MSLD) method incorporating fluid–fluid and fluid-wall interaction is adopted to calculate density profiles in slit nanopores. Subsequently, pore-scale insights are coupled by employing the area-averaged transmissibility in a multicomponent transport model based on the Maxwell-Stefan theory to simulate co– and counter-diffusion processes. The results from the proposed model are compared with results from the homogenous fluid model to analyze deviations caused by neglecting fluid-wall interaction. Results for a ternary hydrocarbon mixture (methane, propane, n-octane) within organic slit nanopores reveal the fluid in nanopores can be categorized into three fluid systems: inhomogeneity dominant (d_a < 3 nm), transition (3 nm < d_a < 30 nm), and homogeneity dominant (d_a > 30 nm) system. The fluid-wall interaction can be neglected in pores larger than 30 nm, while it becomes increasingly significant as pores become smaller. Continuum-scale co– and counter-diffusion simulations further underscore that neglecting fluid inhomogeneity in the inhomogeneity dominant fluid system results in a more than 30 % overestimation of cumulative production/injection. Furthermore, the commonly used modified Peng-Robinson equation of state (PR-EOS) incorporating critical parameter shift leads to even larger discrepancies between predicted and actual production/injection values.