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1. Introduction
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result of pore-scale simulations with and appropriate model representing the
macro-scale behavior, one can study the relation between these two scales.
1.4 Research objectives
This research aims to identify and describe the physical/chemical processes that
govern the transport of both passive and reactive/adsorptive solutes in porous
media by using PNM. We consider mass transfer of reactive/adsorptive solutes
though interfaces, under both saturated and partiality saturated conditions.
While under saturated conditions the interfaces are only those of solid-water
interfaces, under partially saturated conditions, there will be also mass transfer
though air-water interfaces.
This study is aimed at describing steady state Newtonian fluid flow in a rigid
porous medium. During miscible displacement, reactive solutes in a (partially-
) saturated medium are transported in a single fluid phase (water being the
carrier). The most common transport case that one encounters is adsorption,
which, in large, is controlled by the reactivity of the solutes in the fluid phase
and the chemical affinity and physical heterogeneity of the solid phase. In
this study, we have utilized a Multi-Directional Pore-Network (MDPN) model
[Raoof and Hassanizadeh, 2009]. Fundamental laws of physics are applied at
the pore scale, whereas the macroscopic quantities (such as permeability, dispersivity
and average concentrations) are obtained through averaging over the
pore network domain. To meet our objectives we focus on both physical and
topological heterogeneities (different sized pores, variable coordination numbers)
and chemical processes. Hence, we focus on a more realistic microscopic
structure, applying equations of microscopic physics and chemistry and perform
rigorous upscaling. There are many other novel and unique aspects to
this thesis, though which we develop more accurate and realistic schemes to
study flow and transport under partially saturated conditions. For this purpose
we have developed an extensive FORTRAN 90 modular package which covers:
generation of random structure networks; simulation of drainage process; discretization
of pore spaces on the basis of saturation state of each pore; and
solution of flow and reactive transport under both saturated and unsaturated
conditions using several algorithms. The governing equations are solved applying
a fully implicit numerical scheme; however, efficient substitution methods
have been applied which make the algorithm more computationally effective
and appropriate for parallel computations.
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