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| Titel |
Porosities and permeability of Paleozoic sandstones derived from Nuclear Magnetic Resonance measurements |
| VerfasserIn |
Rachel Jorand, Andreas Koch, Oliver Mohnke, Norbert Klitzsch, Christoph Clauser |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035434
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| Zusammenfassung |
| A major obstacle for an increased use of geothermal energy often lies in the high success risk
for the development of geothermal reservoirs due to the unknown rock properties. In general,
the ranges of porosity and permeability in existing compilations of rock properties are too
large to be useful to constrain properties for specific sites. Usually, conservative
assumptions are made about these properties, resulting in greater drilling depth and
increased exploration cost. In this study, data from direct measurements on thirty-three
sandstones from different borehole locations and depths enable to derive statistical
values of the desired hydraulic properties for selected sandstones in the German
subsurface.
We used Nuclear Magnetic Resonance (NMR) measurements to estimate the porosity and the
permeability of sandstones from North Rhine-Westphalia (Germany). Besides NMR standard
poro-perm-measurements were performed on the samples to obtain independent data sets for
comparison. Porosity was measured by Archimedes principle and pore-size distribution by
mercury injection. Also permeability was determined by gas flow measurements taking into
account the Klinkenberg effect.
The porosities of the studied samples vary between 0 % and 16 %. NMR yields suitable
porosity results whereas the porosities obtain by T1 relaxation measurements fit better to the
Archimedes porosities than the porosities obtained by T2 relaxation measurements. For
porosities up to 10 %, T2 relaxation measurements overestimate the porosity. Furthermore,
we calculate the effective porosity using a cutoff time of 3 ms. This effective porosity
agrees much better with Archimedes porosities, particularly for the low porosity
samples.
The gas permeability of studied sandstones varies between 10-21 m2 and 2.10-17 m2. A
large number of empirical relationships between relaxation times and gas permeability
have been published. We have applied several of these relationships to select the
appropriate law for Paleozoic sandstones. The results show that the used models
yield good correlation between gas- and NMR-permeability (R2>0.86 for k>10-19
m2). |
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