『Abstract
Within the framework of the HPF project (Hyperalkaline Plume
in Fractured Rock) at the Grimsel Test Site (Switzerland), a small
scale core infiltration experiment was performed at the University
of Bern. A high-pH solution was continuously injected, under a
constant pressure gradient, into a cylindrical core of granite
containing a fracture. This high-pH solution was a synthetic version
of solutions characteristic of early stages in the degradation
of cement. The interaction between the rock and the solutions
was reflected by significant changes in the composition of the
injected solution and a decrease in the permeability of the rock.
Changes in the mineralogy and porosity of the fault gouge filling
the fracture were only minor. One-dimensional reactive transport
modeling, using a modified version of the GIMRT code, was used
to interpret the results of the experiment. Dispersive and advective
solute transport, mineral reaction kinetics and a coupling between
porosity and permeability changes were taken into account. In
order to obtain a reasonable agreement between models and experimental
results, reactive surface areas of the order of 105
m2/m3 rock had to be used. These values
are much smaller than the values measured for the fault gouge
filling the fracture, which are in the order of 106-107
m2/m3 rock. However, the results could be
improved by adding a small fraction of fine grained mineral, which
could explain the high initial peaks in Al and Si concentration.
With the inclusion of this fine grained fraction, the initial
surface areas in the model were within the range of the measured
specific surface areas of the fault gouge. The fact that the decrease
in permeability was significant despite the minor changes in mineralogy,
suggests that permeability may be controlled by changes in the
structure of the rock (pore geometries) rather than by only the
bulk volumetric (porosity) changes.』
1. Introduction
2. Overview of the experimental methods
3. The model
4. Parameters of the model
4.1. Dimensions
4.2. Rock composition
4.3. Solution composition
4.4. Equilibrium constants
4.5. Reaction rates
4.6. Flow and transport parameters
5. Results and discussion
6. Conclusions
Acknowledgements
References