Seismic signatures of partial saturation on acoustic borehole modes

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Abstract

We present an exact theory of attenuation and dispersion of borehole Stoneley waves propagating along porous rocks containing spherical gas bubbles by using the Biot theory. An effective frequency-dependent fluid bulk modulus is introduced to describe the dynamic (oscillatory) behavior of the gas bubbles. The model includes viscous, thermal, and radiation damping. It is assumed that the gas pockets are larger than the pore size, but smaller than the wavelengths involved (mesoscopic inhomogeneity). A strong dependence of the attenuation of the Stoneley wave on gas fraction and bubble size is found. Attenuation increases with gas fraction over the complete range of studied frequencies (10 Hz–50 kHz). The dependence of the phase velocity on the gas fraction and bubble size is restricted to the lower frequency range. These results indicate that the interpretation of Stoneley wave properties for the determination of, for example, local permeability formation is not straightforward and could be influenced by the presence of gas in the near-wellbore zone. When mud-cake effects are included in the model, the same observations roughly hold, though dependence on the mud-cake stiffness is quite complex. In this case, a clear increase of the damping coefficient with saturation is predicted only at relatively high frequencies
LanguageEnglish
PagesE77-E86
Number of pages10
JournalGeophysics
Volume72
Issue number2
DOIs
StatePublished - 2007

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boreholes
Boreholes
acoustics
borehole
Gases
Acoustics
signatures
saturation
Stoneley wave
bubbles
bubble
gases
gas
mud
damping
attenuation
gas pockets
Damping
viscous damping
Biot theory

Cite this

@article{aea0be0a4db34dbca2d8d2c33887956c,
title = "Seismic signatures of partial saturation on acoustic borehole modes",
abstract = "We present an exact theory of attenuation and dispersion of borehole Stoneley waves propagating along porous rocks containing spherical gas bubbles by using the Biot theory. An effective frequency-dependent fluid bulk modulus is introduced to describe the dynamic (oscillatory) behavior of the gas bubbles. The model includes viscous, thermal, and radiation damping. It is assumed that the gas pockets are larger than the pore size, but smaller than the wavelengths involved (mesoscopic inhomogeneity). A strong dependence of the attenuation of the Stoneley wave on gas fraction and bubble size is found. Attenuation increases with gas fraction over the complete range of studied frequencies (10 Hz–50 kHz). The dependence of the phase velocity on the gas fraction and bubble size is restricted to the lower frequency range. These results indicate that the interpretation of Stoneley wave properties for the determination of, for example, local permeability formation is not straightforward and could be influenced by the presence of gas in the near-wellbore zone. When mud-cake effects are included in the model, the same observations roughly hold, though dependence on the mud-cake stiffness is quite complex. In this case, a clear increase of the damping coefficient with saturation is predicted only at relatively high frequencies",
author = "G.E Chao and D.M.J. Smeulders and {Dongen, van}, M.E.H.",
year = "2007",
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language = "English",
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pages = "E77--E86",
journal = "Geophysics",
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}

Seismic signatures of partial saturation on acoustic borehole modes. / Chao, G.E; Smeulders, D.M.J.; Dongen, van, M.E.H.

In: Geophysics, Vol. 72, No. 2, 2007, p. E77-E86.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Seismic signatures of partial saturation on acoustic borehole modes

AU - Chao,G.E

AU - Smeulders,D.M.J.

AU - Dongen, van,M.E.H.

PY - 2007

Y1 - 2007

N2 - We present an exact theory of attenuation and dispersion of borehole Stoneley waves propagating along porous rocks containing spherical gas bubbles by using the Biot theory. An effective frequency-dependent fluid bulk modulus is introduced to describe the dynamic (oscillatory) behavior of the gas bubbles. The model includes viscous, thermal, and radiation damping. It is assumed that the gas pockets are larger than the pore size, but smaller than the wavelengths involved (mesoscopic inhomogeneity). A strong dependence of the attenuation of the Stoneley wave on gas fraction and bubble size is found. Attenuation increases with gas fraction over the complete range of studied frequencies (10 Hz–50 kHz). The dependence of the phase velocity on the gas fraction and bubble size is restricted to the lower frequency range. These results indicate that the interpretation of Stoneley wave properties for the determination of, for example, local permeability formation is not straightforward and could be influenced by the presence of gas in the near-wellbore zone. When mud-cake effects are included in the model, the same observations roughly hold, though dependence on the mud-cake stiffness is quite complex. In this case, a clear increase of the damping coefficient with saturation is predicted only at relatively high frequencies

AB - We present an exact theory of attenuation and dispersion of borehole Stoneley waves propagating along porous rocks containing spherical gas bubbles by using the Biot theory. An effective frequency-dependent fluid bulk modulus is introduced to describe the dynamic (oscillatory) behavior of the gas bubbles. The model includes viscous, thermal, and radiation damping. It is assumed that the gas pockets are larger than the pore size, but smaller than the wavelengths involved (mesoscopic inhomogeneity). A strong dependence of the attenuation of the Stoneley wave on gas fraction and bubble size is found. Attenuation increases with gas fraction over the complete range of studied frequencies (10 Hz–50 kHz). The dependence of the phase velocity on the gas fraction and bubble size is restricted to the lower frequency range. These results indicate that the interpretation of Stoneley wave properties for the determination of, for example, local permeability formation is not straightforward and could be influenced by the presence of gas in the near-wellbore zone. When mud-cake effects are included in the model, the same observations roughly hold, though dependence on the mud-cake stiffness is quite complex. In this case, a clear increase of the damping coefficient with saturation is predicted only at relatively high frequencies

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DO - 10.1190/1.2431636

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VL - 72

SP - E77-E86

JO - Geophysics

T2 - Geophysics

JF - Geophysics

SN - 0016-8033

IS - 2

ER -