Kinetic approach for modeling salt precipitation in porous-media

Table of Contents

1 Introduction

1.1 Motivation

1.2 Description of the process

1.3 Structure of study

2 Fundamentals

2.1 Porous medium:

2.1.1 Flow in the porous medium:

2.1.2 Multiphase flow in the porous medium:

2.2 Multiphase fluid velocity:

2.2.1 Hydrodynamic dispersion:

2.3 General mass balance for multiphase flow systems:

2.4 Chemistry

2.4.1 Description of Brine:

2.4.2 Important chemical definitions:

3 Model Concept

3.1 Main aspects:

3.2 Thermodynamic equilibrium

3.3 Mass transfer between the phases:

3.3.1 Fluid - Fluid Phases:

3.3.2 Fluid Phase - Solid Phase:

3.4 Transport Equations

3.4.1 Energy balance equation

3.4.2 Mass balance equations

3.4.3 Mass balance for the precipitated NaCl

3.4.4 Source, Sink terms for the model

3.5 Supplementary equations

3.6 Constitutive relationships

3.7 Primary variables

3.8 Numerical Discretization

3.8.1 Spatial Discretization:

3.8.2 Time Discretization:

3.8.3 Solution of the discretized equations:

4 Results

4.1 Scenario setup:

4.2 Scenario 1: Decoupled model - Isothermal case

4.2.1 Results and Discussions:

4.3 Scenario 2: Decoupled model - Non-isothermal case

4.3.1 Scenario setup

4.3.2 Results and Discussions:

4.4 Scenario 3: Comparison of the kinetic approach with the equilibrium approach

5 Summary

5.1 Summary

5.2 Future work

Objectives and Research Themes

This study aims to develop and implement a kinetic model for simulating salt precipitation within porous media. The core research focus lies on addressing the chemical interactions and transport mechanisms of brine components to better understand how salt accumulation affects physical properties like porosity and permeability, with a specific comparison against existing equilibrium-based models.

• Kinetic modeling of sodium chloride (NaCl) precipitation in porous media.
• Implementation and testing within the DuMux framework using the 2pncmin model.
• Investigation of isothermal and non-isothermal conditions on salt accumulation.
• Evaluation of mass transfer, evaporation effects, and porosity-permeability relationships.
• Comparative analysis of kinetic versus equilibrium-based precipitation approaches.

Excerpt from the Book

Summary of Chapters

1 Introduction: Provides the background and motivation for studying soil salinization, defines the process, and outlines the structure of the independent study.

2 Fundamentals: Introduces the basic theory regarding porous media, multiphase flow, mass balance, and chemical definitions relevant to brine and salt precipitation.

3 Model Concept: Details the conceptual framework, transport equations, numerical discretization methods, and the approach used for the kinetic model.

4 Results: Presents the findings from three specific scenarios, including isothermal and non-isothermal simulations and a comparison with equilibrium-based modeling.

5 Summary: Concludes the analysis by reviewing the implemented model, discussing the observed limitations, and suggesting directions for future research.

Keywords

Salt precipitation, Porous media, Salinization, Kinetic approach, Numerical modeling, DuMux, Multiphase flow, Brine, Evaporation, Porosity reduction, Permeability, Thermodynamic equilibrium, Mass transport, Isothermal case, Non-isothermal case

Frequently Asked Questions

What is the primary motivation for this research?

The research is motivated by the global challenge of soil salinization, which poses a severe threat to agricultural productivity due to salt accumulation in porous media.

What is the core objective of the work?

The goal is to develop and implement a kinetic approach for modeling salt precipitation, which allows for a more detailed analysis than traditional equilibrium-based models.

Which simulator framework is used for the model implementation?

The numerical model is implemented within the DuMux simulator framework, which is built on the DUNE (Distributed and Unified Numerics Environment) architecture.

What primary components are tracked in this system?

The model focuses on four main components: water (w), air (a), and sodium (Na+) and chloride (Cl−) ions.

How is the spatial discretization handled?

Spatial discretization is performed using the BOX method, which combines finite element and finite volume methods to ensure accurate flux calculations on unstructured grids.

What are the key differences between the kinetic and equilibrium approaches?

While equilibrium approaches assume precipitation occurs instantly at the solubility limit, the kinetic approach models the rate of precipitation as a function of the saturation index, providing a more dynamic representation.

How is the permeability of the medium affected by salt precipitation?

Salt precipitation reduces the available pore space, which in turn decreases the porosity. The study uses the Kozeny-Carman relation to calculate the resulting reduction in permeability.

What challenge arises at low water saturation levels?

The study notes that at very low water saturation levels, mass fraction calculations can become unstable, suggesting a need for further refinement in the model's interfacial surface area calculations.