Page 132 - Fundamentals of Computational Geoscience Numerical Methods and Algorithms

Chapter 6
A Decoupling Procedure for Simulating Fluid

Mixing, Heat Transfer and Non-Equilibrium
Redox Chemical Reactions in Fluid-Saturated
Porous Rocks

Non-equilibrium redox chemical reactions of high orders are ubiquitous in
fluid-saturated porous rocks within the crust of the Earth. They play a very impor-
tant role in ore body formation and alteration closely associated with a miner-
alizing system. Since pore-fluid is a major carrier transporting chemical species
from one part of the crust into another, the chemical process is coupled with
the pore-fluid flow process in fluid-saturated porous rocks. In addition, if the
rate of a chemical reaction is dependent on temperature, the chemical process is
also coupled with the heat transfer process. When a pore-fluid carrying one type
of chemical species meets with that carrying another type of chemical species,
these two types of pore-fluids can mix together to allow the related chemical
reaction to take place due to solute molecular diffusion/dispersion and advec-
tion. For these reasons, the resulting patterns of mineral dissolution, transporta-
tion, precipitation and rock alteration are a direct consequence of coupled processes
between fluids mixing, heat transfer and chemical reactions in fluid-saturated porous
rocks.
Due to ever-increasing demands for minerals and possible exhaustion of the
existing mineral deposits in the foreseeable future, understanding the controlling
mechanisms behind ore body formation and mineralization within the upper crust
of the Earth becomes a very important research field. There is no doubt that an
improved understanding of ore forming processes can significantly promote mineral
exploration for new ore deposits within the upper crust of the Earth. Although exten-
sive studies have been carried out to understand the possible physical and chemical
processes associated with ore body formation and mineralization (Phillips 1991, Yeh
and Tripathi 1991, Nield and Bejan 1992, Steefel and Lasaga 1994, Raffensperger
and Garven 1995, Schafer et al. 1998a, b, Zhao et al. 1997a, 1998a, 1999b, Xu
et al. 1999, Zhao et al. 2000b, 2001b, 2001d, 2002c, Schaubs and Zhao 2002, Ord
et al. 2002, Gow et al. 2002, Zhao et al. 2003a), the kinetics of a redox chemi-
cal reaction and its interaction with physical processes are often overlooked in the
numerical modelling of ore forming systems. In most chemical reactions associated
with an ore forming system, the chemical reaction rate is finite so that an interaction
between the solute molecular diffusion/dispersion, advection and chemical kinetics
must be considered.

C. Zhao et al., Fundamentals of Computational Geoscience, 121
Lecture Notes in Earth Sciences 122, DOI 10.1007/978-3-540-89743-9 6,
C Springer-Verlag Berlin Heidelberg 2009