Impact of Synthetic Porous Medium Geometric Properties on Solute Transport Using Direct 3D Pore-Scale Simulations

Paolo Roberto Di Palma,Andrea Parmigiani,Christian Huber,Emanuele Romano,Nicolas Guyennon,Falk Heβe

doi:10.1155/2019/6810467

Abstract

Transport processes in porous media have been traditionally studied through the parameterization of macroscale properties, by means of volume-averaging or upscaling methods over a representative elementary volume. The possibility of upscaling results from pore-scale simulations, to obtain volume-averaging properties useful for practical purpose, can enhance the understanding of transport effects that manifest at larger scales. Several studies have been carried out to investigate the impact of the geometric properties of porous media on transport processes for solute species. However, the range of pore-scale geometric properties, which can be investigated, is usually limited to the number of samples acquired from microcomputed tomography images of real porous media. The present study takes advantage of synthetic porous medium generation to propose a systematic analysis of the relationships between geometric features of the porous media and transport processes through direct simulations of fluid flow and advection-diffusion of a non-reactive solute. Numerical simulations are performed with the lattice Boltzmann method on synthetic media generated with a geostatistically based approach. Our findings suggest that the advective transport is primarily affected by the specific surface area and the mean curvature of the porous medium, while the effective diffusion coefficient scales as the inverse of the tortuosity squared. Finally, the possibility of estimating the hydrodynamic dispersion coefficient knowing only the geometric properties of porous media and the applied pressure gradient has been tested, within the range of tested porous media, against advection-diffusion simulations at low Reynolds (<10-1) and Peclet numbers ranging from 101 to 10-2.

Highlights

A quantitative relation between the structure of porous media and its effect on solute transport is fundamental to our understanding of groundwater contamination dynamics and the development of pollutant remediation strategies [1]
For a detailed discussion about semivariogram functions adopted in the geostatistical model, we address the interested readers to Di Palma et al [23]
This study investigates the impact of various porous medium geometric descriptors on the transport of non-reactive solutes

Summary

Introduction

A quantitative relation between the structure of porous media and its effect on solute transport is fundamental to our understanding of groundwater contamination dynamics and the development of pollutant remediation strategies [1]. Transport processes in porous media have been traditionally studied through the parametrization of macroscale properties (e.g., hydraulic conductivity or hydrodynamic dispersion coefficients) by means of volume-averaging or upscaling methods over a representative elementary volume. These upscaling approaches are not valid when considering length scales on the order of a single pore or the complexity of processes (i.e., physical, chemical, and biological) that take place at the pore scale [2]. A statistical approach to generate media with given imposed structural features can be a cost-effective means for producing large numbers of realizations that represent those features of natural samples deemed relevant. The two approaches that are commonly used to generate synthetic porous media can be divided into statistical models (e.g., multipoint statistics and autocorrelation functions) and object-based methods, where geometrical objects are randomly placed in a domain to simulate diagenesis processes [8]

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