Intro to Modeling Porous Media Flow with COMSOL Multiphysics^®

COMSOL Multiphysics is a finite element-based simulation package that enables the modeling of porous media flow. It provides a comprehensive interface for simulating a wide range of physical phenomena, including fluid, structural, and acoustic applications relevant to porous media. The software allows users to couple different physics types together using add-on modules, such as CFD, subsurface flow, microfluidics, chemical reaction engineering, and batteries and fuel cells, all of which support dedicated porous media flow applications. Additionally, COMSOL Multiphysics includes an application builder for designing custom user interfaces, facilitating streamlined simulation processes. Porous media are multi-phase systems with at least one solid immobile phase and one fluid phase, though multiple fluid and solid phases can be incorporated. Simulating porous media involves complex geometries at the pore scale, which can be computationally expensive. COMSOL Multiphysics offers a more economical approach by homogenizing these geometries, allowing for macro-scale simulations while accounting for local pore-scale effects using average quantities like porosity and permeability. This approach avoids the need for meshing complex geometries and enables efficient modeling of large-scale systems such as well reservoirs. COMSOL Multiphysics provides various physics interfaces for solving flow through porous media. These include fully resolved single-phase flow using laminar or creeping flow, homogenized approaches with Brinkman equations for fast flow, Darcy's law for slow flow, and fracture flow for thin porous regions. The software also supports two-phase porous flow using the Richards equation for variably saturated flow and the two-phase Darcy's law. A key strength of COMSOL is its ability to couple different physics interfaces, allowing for continuous pressure and velocity fields in simulations that combine free flow and porous media flow. The software's capabilities are demonstrated through a live example of modeling pore-scale flow to determine porosity and permeability, which can then be applied to a homogenized macro-scale model. Users can define their own equations in COMSOL Multiphysics, offering flexibility for custom retention and storage models. The software supports both fully resolved and homogenized approaches to multi-phase flow, with options for detailed tracking of fluid interfaces using modules like CFD and microfluidics. For further resources, COMSOL offers an introduction booklet, tutorials, and blogs on its website, including guidance on selecting the appropriate porous media and subsurface flow interfaces. Users are encouraged to participate in COMSOL conferences and can request live demos to explore the software's capabilities. Contact information is available for those seeking additional support or information.