download pdf version of PhD book - Universiteit Utrecht

1. Introduction
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
solute transport processes are simulated directly at the microscopic scale without
assuming a priori the traditional macroscopic equations (such as the famous
Darcy law). This is done by creating a simulated porous medium made
by pore bodies and pore throats of different sizes (the “geometry” of the
porous medium) variably connected to each other (the “topology” of the porous
medium) and then simulating through this network the fluid flow and (reactive)
solute transport process of interest at the microscale, with the relevant
physics implemented on a pore to pore basis. Compared to other pore scale
modeling methods, such as the lattice-Boltzmann method, pore-network models
are computationally effective. Recent advances have allowed modeling a
degree of irregularity in pore cross-sectional shape that was not available in
earlier PNMs. In addition, pore-network models are capable of incorporating
some important statistical characteristics of porous media such as pore sizes
[Øren et al., 1998b, Lindquist et al., 2000], coordination number distributions
[Raoof and Hassanizadeh, 2009] and topological parameters such as Euler number
[Vogel and Roth, 2001].
Pore network modeling can provide flow, relative permeabilities, capillary pressures
and solute concentration data in an efficient way, which could be difficult
to measure through experimental methods. In addition, using PNM, one can
explore the sensitivity of these data to a variety of different conditions. Indeed
the scope for utilization of PNM is in fact much wider and extends to the
study and optimization of a variety of transport processes and to most of those
cases where laboratory investigation would be long, costly or technically very
difficult. As examples, pore-network models have been widely used to study:
multiphase flow in porous media [Celia et al., 1995, Blunt, 2001, Joekar-Niasar
et al., 2008b, 2010]; chemical and biological processes, such as the dissolution of
organic liquids [Zhou et al., 2000b, Held and Celia, 2001, Knutson et al., 2001b];
biomass growth [Suchomel et al., 1998c, Kim and Fogler, 2000, Dupin et al.,
2001]; and adsorption [Sugita et al., 1995b, Acharya et al., 2005b, Li et al.,
2006b]. In recent pore-scale modeling, various types of adsorption reactions
have been used: linear equilibrium (e.g., Raoof and Hassanizadeh [2009]) and
nonlinear equilibrium [Acharya et al., 2005b]; kinetic adsorption (e.g., Zhang
et al. [2008]); and heterogeneous adsorption in which adsorption parameters
were spatially varying (e.g., Zhang et al. [2008]).
Pore geometry and topology have a major influence on solute transport and/or
multiphase flow in porous systems. Sok et al. [2002] concluded that it is extremely
important to ensure that a pore-network model captures the main
6