Enhanced Condensation of Water Vapor in Nanoporous Media: Numerical Studies Using the Square-Gradient Density Functional Theory

Abstract:

The ability to predict multiphase fluid transport in nanoporous rocks is critical for many geoscience applications, such as unconventional oil and gas production, geologic carbon sequestration or nuclear waste disposal. When the pore sizes approach nanoscales, physicochemical interactions among fluid and solid phases can alter equilibrium phase compositions in nanoscale pores. Likewise, the fluid–solid interactions, in addition to the effect of pore connectivity, can control basic macroscopic transport properties of porous media such as permeability and diffusivity. Recent experimental research has shown the importance of fluid-solid interfacial interactions on nanoconfined multiphase fluid behavior in nanoporous media including shale. For example, when nanoporous samples are exposed to water vapor at their inlet boundaries under relative humidity conditions below the vapor saturation values, a liquid-like water forms near the inlet, and subsequently the water condensed migrates inside the samples. This apparent enhanced condensation and condensation–induced imbibition are believed to result from the molecular interactions between water and solid that become more pronounced under nanoconfinement. We recently developed a new numerical model based on the square-gradient density functional theory to investigate the enhanced condensation of water at pore and macroscopic scales of nanoporous media. The model takes into account the surface tension forces between different fluid phases and the attractive and repulsive interaction forces between fluids and solids. This presentation will include preliminary results of the pore-scale numerical model to study the effects of the fluid-solid interaction forces and pore space geometry on enhanced condensation and water transport in a rigid uncharged nanoporous medium.