Compositional two-phase flow and phase behavior in nanoporous media: pore-level physics, pore-network modeling, and upscaling

Multiphase fluid flow and multicomponent transport in porous media are often controlled by thermodynamic phase change dynamics. In a nanometer-scale pore space, the phase behavior of a multicomponent fluid deviates from that in a larger pore space (i.e., micrometer or greater)—the pressure and temperature at which the fluid begins to evaporate or condensate in nanopores can significantly differ from those in large pores. This pore size-dependent phase change behavior is further complicated in natural nanoporous media (e.g., clay soil or shale rock) that often contain a significant fraction of interconnected pores spanning from nanometers to micrometers. While the nanoconfined phase behavior in a single nanopore has been extensively studied by molecular-level theories, the new molecular-level understanding has not yet been incorporated in Darcy-scale continuum models.

We address this challenge of scale translation by developing a new pore-network-scale modeling framework for flow, transport, and thermodynamics in nanoporous media. The new modeling framework is comprised of 1) a phase-equilibrium model that accounts for the pore-size and -geometry dependent nanoconfinement effects and 2) a fully implicit dynamic pore-network model framework coupling the individual-pore nanoconfined phase-equilibrium model with the two-phase compositional flow. This framework for the first time allows us to investigate the interactions between compositional flow dynamics and nanoconfined phase behaviors at an REV-scale, which we will illustrate by a series of numerical experiments on complex networks with pores varying in size, geometry, and wettability.