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| Titel |
Local regularity analysis of strata heterogeneities from sonic logs |
| VerfasserIn |
S. Gaci, N. Zaourar, M. Hamoudi, M. Holschneider |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 17, no. 5 ; Nr. 17, no. 5 (2010-09-20), S.455-466 |
| Datensatznummer |
250013725
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| Publikation (Nr.) |
 copernicus.org/npg-17-455-2010.pdf |
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| Zusammenfassung |
Borehole logs provide geological information about the rocks crossed by the
wells. Several properties of rocks can be interpreted in terms of lithology,
type and quantity of the fluid filling the pores and fractures.
Here, the logs are assumed to be nonhomogeneous Brownian motions (nhBms)
which are generalized fractional Brownian motions (fBms) indexed by
depth-dependent Hurst parameters H(z). Three techniques, the local wavelet
approach (LWA), the average-local wavelet approach (ALWA), and Peltier
Algorithm (PA), are suggested to estimate the Hurst functions (or the
regularity profiles) from the logs.
First, two synthetic sonic logs with different parameters, shaped by the
successive random additions (SRA) algorithm, are used to demonstrate the
potential of the proposed methods. The obtained Hurst functions are close to
the theoretical Hurst functions. Besides, the transitions between the modeled
layers are marked by Hurst values discontinuities. It is also shown that PA
leads to the best Hurst value estimations.
Second, we investigate the multifractional property of sonic logs data recorded
at two scientific deep boreholes: the pilot hole VB and the ultra deep main
hole HB, drilled for the German Continental Deep Drilling Program (KTB). All
the regularity profiles independently obtained for the logs provide a clear
correlation with lithology, and from each regularity profile, we derive a
similar segmentation in terms of lithological units. The lithological
discontinuities (strata' bounds and faults contacts) are located at the local
extrema of the Hurst functions. Moreover, the regularity profiles are
compared with the KTB estimated porosity logs, showing a significant relation
between the local extrema of the Hurst functions and the fluid-filled
fractures. The Hurst function may then constitute a tool to characterize
underground heterogeneities. |
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