Investigation of fracture-matrix interaction: Preliminary experiments in a simple system Page: 4 of 32
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mm and were fired at 6560C for 696 min. The
porosity of both plates was measured by
gravimetric means to be approximately 0.30.
During the experiment, constant pressure boundary
conditions were maintained around the edge of the
slab to allow air to escape. The experiment was
started by supplying a steady flow of potassium
iodide (KI) solution (10% by weight) to the top
of the vertical fracture. The solution was
pumped at a constant rate of 1.7 ml/min through a
25 gauge needle inserted into a 1 mm I.D.
capillary tube which was centered over the top of
the fracture. KI was used to increase the x-ray
absorption of the wetting solution and hence
improve image contrast. A light suction imposed
by aspiration was applied at the bottom of the
fracture to prevent the build-up of fluid along
the lower boundary. Thus the experiment
simulated the top of a much longer fracture-
matrix system.
Moisture content fields were captured
incrementally in time during the transient water
imbibition phase of the experiment using the x-
ray adsorption method developed by Tidwell and
Glass.15 X-ray sensitive film (Kodak Industrial
AA sheet film) was placed on the back of the
fracture-matrix slab and exposed by an industrial
x-ray unit set at 60 kilovolts and 18 miliamps
(100 sec for tuff, 60 sec for analog to achieve
optimum contrast).
Following complete saturation of the fracture-
matrix system, the injection solution was
switched to pure deionized water (DeI). A series
of exposures were taken to explore the flushing
of the KI solution from the fracture-matrix
system. This component of the experiment was
designed to demonstrate the capabilities of the
x-ray absorption technique to image transient
solute concentration fields.
Once the x-ray film was developed, a 512 x 512
array CCD camera and IBM 486 PC-based frame
grabber were used to digitize the radiograph at
256 grey-levels of resolution. Using step-wedge
information appearing in each image, data were
adjusted for minor systematic variations in field
strengths, film, and equipment characteristics.15
X-ray absorption theory was used to convert each
of the 262,144 data points within the
two-dimensional field into saturation values.'5
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Foltz, S. D.; Tidwell, V. C.; Glass, R. J. & Sobolik, S. R. Investigation of fracture-matrix interaction: Preliminary experiments in a simple system, article, December 31, 1992; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc627381/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.