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| Titel |
2D porosity mapping and distribution in an organic rich shale from the Middle East: preliminary results using a broad ion beam - scanning electron microscopy (BIB-SEM) approach |
| VerfasserIn |
Jop Klaver, Guillaume Desbois, Janos Urai |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046859
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| Zusammenfassung |
| Conventional methods of determining porosity and permeability in shales have their
difficulties to accurately measure these when it comes to very tight rocks. In comparison, the
complementary approach of porosity imaging and mapping in shales was enabled and has
seen major advances recently in providing smooth, damage free surfaces in reasonable
timeframes using ion beam cutting techniques. As mapped areas are very small compared
to macrostructural heterogeneities in the investigated rocks, the broad ion beam
cutting and polishing technique has been seen as a valuable opportunity to use
microstructural characterization techniques in determining bulk rock properties in
homogeneous sections and to mitigate the upscaling problem of this approach to a
certain extent. We present here first results of a combined semi-automated effort to
map and characterize porosity in terms of its distribution related to mineralogy
and orientation using a broad ion beam cutting technique in combination with a
conventional high resolution SEM. Using a BIB cross-section polisher, the extent of the
polished surfaces was enlarged by a factor of thousand compared to focused ion beam
techniques and covers an area of approximately 1 mm2. Image resolution of the
conventional SEM used in this study allows investigation of pores down to the nanometer
scale.
From the large BIB polished surface area, porosity was traced in certain representative
intervals in using advanced image analysis techniques. Pores detected are segmented from
mosaics of secondary electron (SE) images to be statistically interpreted. Identification and
mapping of mineral phases were performed using grey values from backscattered electron
(BSE) images verified and calibrated by a combination of EDX and bulk XRD
analyses.
Two adjacent organic rich core samples from a shale interval in the Middle
East were investigated. Based on more than 13000 detected pores, porosity could
be classified into two major pore?size classes. Relative large pores (> 0.5μm2)
typically found in the organic matter?rich intervals. Their distribution contributes
strongly to the overall porosity content of the shale. However the far majority of the
pores found have equivalent radius less than 400nm and with areas below 0.5μm2.
Including these latter pore class, the inferred porosity from both samples gives
similar results in the order of |
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