Nanometer-scale imaging and pore-scale fluid flow modeling inchalk Page: 2 of 16
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modeling approach enjoyed a significant interest from the researchers and resulted in theoretically and
practically sound conclusions ( Oren et al., 1998; Patzek, 2001; Blunt, 2001), we feel that direct pore space
analysis deserves more attention. In addition, direct analysis of the pore space provides an opportunity to study
alteration of the rock flow properties, e.g., due to mechanical transformations or mineralization (Jin et al.,
c 10Opm D 10pUm
Figure 1. FIB images of diatomite(A) and chalk (C) and 3D reconstructions (B,D)
The FIB apparatus used in this study is model FEI Strata DB235, dual electron and ion beam. It is a scanning
electron microscope (SEM) that has also the capability to focus gallium ions (Ga+) accelerated by potentials up
to 30kV. Both, secondary electrons and secondary ions can be used for imaging and the digitized images are
stored in 1024x954, 8 bit, TIF format. The image contrast is determined both by the topography of the sample
and by the difference in the atomic numbers of the materials present at the sample surface. Thus, a good
pore/grain contrast can be achieved for both epoxy-impregnated and nonimpregnated samples. To avoid
damaging the sample by the ion beam during imaging, a low beam current (10-100 pA) and/or a short imaging
time (seconds) are recommended. During milling, the ion beam current can be increased by orders of
magnitude (up to 20,000 pA) and the exposure time can be increased up to hours. An important feature of the
instrument is a 5-axis computer-controlled stage, which allows for repeatable access to the same location on the
sample surface. The stage allows for the sample orientation either normal to the ion beam for drilling submicron
scale patterns, or quasi parallel for milling successive layers. The large sample chamber and the number of
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Tomutsa, Liviu; Silin, Dmitriy & Radmilovich, Velimir. Nanometer-scale imaging and pore-scale fluid flow modeling inchalk, article, August 23, 2005; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc893671/m1/2/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.