Dual Porosity & Dual Permeability Modeling

The concept of dual porosity and dual permeability is a valuable framework used to describe the flow of fluids within porous media, taking into account the existence of two distinct types of pores. Typically, one type of pore is significantly smaller and is referred to as “micropores”, while the other type is notably larger and is known as “macropores”. This concept finds widespread application in various fields, including subsurface hydrology, petroleum engineering, environmental science, and geology, aiding in the comprehension of fluid movement within porous materials. For instance, it is particularly relevant in scenarios involving fissured rocks or the upper soil layer, where macropores may resemble wormholes.

While the terms “dual porosity” and “dual permeability” are occasionally employed interchangeably and inconsistently in the literature, within COMSOL Multiphysics, three distinct features are provided under the following names:

Here, the flow through macropores is typically governed by Darcy's law where the micropores do not significantly contribute to the overall flow in the porous medium. This assumption can be made because the macropores, due to their larger size and higher permeability, dominate the flow behavior. While micropores may not actively participate in the flow, they are considered in terms of fluid exchange with the macropores.

In practical terms, the is employed when you have a porous medium where most of the flow occurs through a well-connected network of macropores, and the contribution of the smaller micropores can be safely neglected. This simplifies the modeling process while still allowing you to capture the essential features of the system's behavior. It's a valuable tool in various fields, including hydrogeology, where it can be used to simulate the movement of groundwater in complex geological formations.

This feature can be applied in scenarios where the porous medium is saturated with a fluid. One key difference between dual permeability and dual porosity is that, in a dual permeability medium, both macro- and micropores contribute significantly to the flow field. This means that Darcy's law, which governs fluid flow through porous media, is applied to both pore types. In other words, the flow rates through both macropores and micropores are considered. It can be applied to situations where both pore types have varying permeabilities. This is in contrast to the dual porosity approach where it is assumed that one material is highly permeable and the other is not.

In practical terms, the is used when modeling saturated fluid flow in a porous medium with a complex internal structure that includes both micropores and macropores, and where both pore types significantly influence the overall flow behavior. This modeling approach is particularly valuable in fields such as subsurface hydrology, petroleum reservoir engineering, and geology, where reservoirs or aquifers exhibit dual permeability characteristics.

This feature extends the concept of having two types of pores within the porous medium. Fluid flow through macro- and micropores is described by the Richards' Equation and is solved separately for both the macropores and micropores, accounting for the differing flow dynamics in each. This accounts for the heterogeneous nature of unsaturated porous media which is particularly valuable for simulating real-world subsurface environments where the presence of both matrix and fractures/channels significantly affects fluid flow, such as in soil profiles or fractured rock formations. It provides a more realistic representation of fluid movement in these environments compared to models that assume homogeneous behavior.

In summary, the is designed to address the complexities of fluid flow in unsaturated porous media by considering the presence of both macro- and micropores, each governed by Richards' Equation. This approach enhances the accuracy and realism of subsurface simulations in situations where unsaturated conditions are prevalent, leading to more informed decisions in various scientific and engineering applications.