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| Titel |
X-ray imaging during capillary imbibition: a study on how compaction bands impact fluid flow in Bentheim sandstone |
| VerfasserIn |
Adeline Pons, David Christian, Jerome Fortin, Sergei Stanchits, Jean-Marie Mengus |
| 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 |
250046284
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| Zusammenfassung |
| In porous sedimentary rocks, strain localization commonly develops along shear bands or
compaction bands. Whereas shear localization is associated with dilatant or compactive
volumetric strain, compaction band is always associated with a drastic reduction in porosity,
thus such a localized mode of failure can significantly impact the regional fluid
flow.
To investigate the effect of compaction bands (CB) on fluid flow, capillary imbibition
experiments were performed on Bentheim sandstone specimens (initial porosity ~22.7%)
using an industrial X-ray scanner. We used a three steps procedure combining 1) X-ray
imaging of capillary rise in intact Bentheim sandstone, 2) formation of compaction band
under triaxial tests, at 185 MPa effective pressure, with acoustic emissions (AE) recording for
localization of the induced damage, and 3) again X-ray imaging of capillary rise in the
damaged specimens after the unloading.
The experiments were performed on intact cylindrical specimens, 5 cm in diameter
and 10.5 cm in length, cored in different orientations (parallel or perpendicular to
the bedding). Analysis of the images obtained at different stages of the capillary
imbibition shows that the presence of CB slows down the imbibition and disturbs the
geometry of water flow. In addition we show that the CB geometry derived from X-ray
density maps analysis is well correlated with AE location obtained during triaxial
test.
The analysis of the water front kinetics was conducted using a simple theoretical model,
which allowed us to confirm that compaction bands act as a barrier for fluid flow, not fully
impermeable though. We estimate a contrast of permeability of a factor ~3 between the host
rock and the compaction bands. This estimation of the permeability inside the compaction
band is consistent with estimations done in similar sandstones from field studies, but differs
by one order of magnitude from estimations from previous laboratory measurements. |
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