Multiscale filtration framework with nanoconfined phase behavior: Pore Network Modeling with Density Functional Theory calculations

TL;DR

The paper addresses the challenge of upscaling fluid transport in multiscale porous media by capturing nanoscale confinement effects, specifically capillary condensation and hysteresis, within a PNM framework. It introduces a coupled PNM–DFT workflow where DFT yields nanoconfined PVT and condensation conditions that block pores in the network, enabling permeability predictions along pressure isotherms and across thermodynamic paths. The study demonstrates that permeability reductions depend strongly on pore-space geometry, PSD, sample size, and structural interconnectivity, with capillary hysteresis shifting the onset of blockage and altering the permeability-pressure response. This framework offers a path toward more accurate upscaling of multiscale filtration phenomena and informs the design and interpretation of representative nanoscale data for upscaled porous media models.

Abstract

The simulation of fluid flow in real, multiscale porous media remains challenging due to the complexity of nanoscale phenomena and the difficulty of developing upscaling methodologies. In this study, we introduce a multiscale filtration framework based on Pore Network Modeling, incorporating the effects of pore blockage resulting from capillary condensation of fluid in the nanoporous space. To accurately predict capillary condensation in nanoconfinement, we apply classical Density Functional Theory calculations along with the consideration of capillary hysteresis. The pores blocked by condensate are excluded from the fluid flow, leading to a drop in permeability of the porous space. Our findings demonstrate that the resulting permeability is strongly dependent on the geometry of porous space, including pore size distribution, sample size, and the particular structure of the sample, along with thermodynamic conditions and processes, specifically, pressure growth or reduction. Overall, the presented research contributes valuable insights into multiscale transport phenomena and facilitates the advancement of upscaling techniques.

Figures (11)

• Figure 1: Schematic illustration of fluid properties in nanoporous media.
• Figure 2: Mock-up of the image, where the channels with capillary condensation are blocked.
• Figure 3: Density profiles of carbon dioxide at T = 298 K and P = 1 and 5 MPa in the pore H = 3 nm, where the dashed lines correspond to the bulk density, are shown.
• Figure 4: PVT for $CO_2$ at T = 298 K during pressure increase up to 10 MPa in the bulk and in the pores H = 3, 5, and 8 nm.
• Figure 5: Pressures of capillary condensation for $CO_2$ in the pores H = 3-20 nm at T = 298 K during pressure increase and decrease. Inset: PVT hysteresis at H = 8 nm.