Granite microporosity changes due to fracturing and alteration: secondary mineral phases as proxies for porosity and permeability estimation
<p>Several alteration facies of fractured Lipnice granite are studied in detail on borehole samples by means of mercury intrusion porosimetry, polarized and fluorescent light microscopy, and microprobe chemical analyses. The goal is to describe the granite void space geometry in the vicinity o...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-02-01
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| Series: | Solid Earth |
| Online Access: | https://www.solid-earth.net/10/251/2019/se-10-251-2019.pdf |
| Summary: | <p>Several alteration facies of fractured Lipnice granite are
studied in detail on borehole samples by means of mercury intrusion porosimetry,
polarized and fluorescent light microscopy, and microprobe chemical analyses. The goal is
to describe the granite void space geometry in the vicinity of fractures with alteration
halos and to link specific geometries with simply detectable parameters to facilitate
quick estimation of porosity and permeability based on, for example, drill cuttings. The
core of the study is the results of porosity and throat size distribution analyses on 21
specimens representing unique combinations of fracture-related structures within six
different alteration facies basically differing in secondary phyllosilicate chemistry and
porosity structure. Based on a simple model to calculate permeability from the measured
porosities and throat size distributions, the difference in permeability between the
fresh granite and the most fractured and altered granite is 5 orders of magnitude. Our
observations suggest that the porosity, the size of connections and the proportion of
crack porosity increase with fracture density, while precipitation of iron-rich infills
as well as of fine-grained secondary phyllosilicates acts in the opposite way. Different
styles and intensities of such end-member agents shape the final void space geometry and
imply various combinations of storage, transport and retardation capacity for specific
structures. This study also shows the possibility to use standard mercury intrusion
porosimetry with advanced experimental settings and data treatment to distinguish
important differences in void space geometry within a span of a few percent of porosity.</p> |
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| ISSN: | 1869-9510 1869-9529 |