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| Titel |
Geomechanical and anisotropic acoustic properties of Lower Jurassic Posidonia shales from Whitby (UK) |
| VerfasserIn |
Alimzhan Zhubayev, Maartje Houben, David Smeulders, Auke Barnhoorn |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250095774
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| Publikation (Nr.) |
 EGU/EGU2014-11246.pdf |
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| Zusammenfassung |
| The Posidonia Shale Formation (PSF) is one of the possible resource shales for
unconventional gas in Northern Europe and currently is of great interest to hydrocarbon
exploration and production. Due to low permeability of shales, economically viable
production requires hydraulic fracturing of the reservoir. The design of hydrofractures
requires an estimate of stress state within the reservoir and geomechanical properties such as
Young’s modulus and Poisson’s ratio.
Shales are often highly anisotropic and the models which neglect shale anisotropy may
fail to predict the behaviour of hydrofractures. Seismic attenuation anisotropy, on
the other hand, can play a key role in quantitative rock characterization. Where
the attenuation anisotropy can potentially be linked to anisotropic permeability of
shales, its fluid/gas saturation and preferred development of anisotropic fracture
orientations.
In this research, by utilizing the so-called Thomsen’s notations, the elastic anisotropy of
our (fractured and unfractured) shales has been investigated using a pulse transmission
technique in the ultrasonic frequency range (0.3-1 MHz). Assuming transverse isotropy of
the shales, and taking the axis x3 as the axis of rotational symmetry, directional
Young’s moduli and Poisson’s ratios were obtained. The Young’s modulus measured
parallel to bedding (E1) is found to be larger than the Young’s modulus measured
orthogonal to bedding (E3). In case of the Poisson’s ratios, we found that ν31 is
larger than ν12, where νijrelates elastic strain in xj direction to stress applied in xi
direction.
Finally, attenuation anisotropy in dry and layer-parallel fractured Posidonia shale samples
has been studied in the same frequency range. The attenuation of compressional (QP-1) and
shear (QS-1) waves increases substantially with a macro (or wavelength) fracture
introduction, especially for P and S waves propagating orthogonal to the bedding. In
non-fractured and fractured dry shales, QP-1 is always larger than QS-1. This inequality
was also found for the fractured shale using different fluids (water, oil) on the fracture
surface. A high-viscosity fluid decreases QP-1 and QS-1 in both (orthogonal and parallel to
the bedding) directions, and the QP-1 to QS-1 ratio decreases with the increase of fluid
viscosity. |
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