14. Anisotropic Permeability: Influence on Seismic Velocity and Attenuation

Gelinsky, Stephan; Shapiro, Serge A.

doi:10.1190/1.9781560802693.ch14

Cited by 7 publications

(4 citation statements)

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“…The mechanisms give a directional attenuation, with the greatest being perpendicular to the crack strike at all frequencies. This response is similar to that predicted by Mavko and Nur (1979), but orthogonal to that predicted by Gelinsky and Shapiro (1995) at seismic frequencies. For seismic frequencies and the physical conditions of most hydrocarbon reservoirs, the process of flow between the aligned Hudson cracks is calculated to be ineffective, and they remain isolated.…”

Section: Some Specific Fluid Flow Mechanismssupporting

confidence: 75%

“…Both the permeability and the elasticity are assumed to possess TIH symmetry (transverse isotropy with a horizontal symmetry axis), thus implying fractures as an underlying causative mechanism. Gelinsky and Shapiro (1995) conclude that, at seismic frequencies, velocity anisotropy must be dominated by the rock frame, whereas the attenuation anisotropy is strongly influenced by the permeability. Both P-and shear-waves are influenced by the permeability-induced dissipation process, and exhibit attenuation and a concomitant velocity dispersion.…”

Section: Some Specific Fluid Flow Mechanismsmentioning

confidence: 82%

“…Another fluid-flow mechanism discussed during the course of this workshop was that of Gelinsky and Shapiro (1995). It is likely to be a dominant cause of attenuation in the sonic log and cross-well kilohertz range, but not in the seismic frequency range.…”

Section: Some Specific Fluid Flow Mechanismsmentioning

confidence: 99%

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Azimuthal variation inP-wave signatures due to fluid flow

MacBeth

1999

GEOPHYSICS

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The favored dominant mechanism for attenuation in the upper crust at seismic frequencies is intracrack fluid flow. In cracked media, the azimuthal attenuation of the P-wave amplitudes arising from such flow is predicted to be quite substantial. The consequence of this variation in azimuth is a modification in the amplitude behavior of the base event from a cracked reservoir due to transmission through the attenuative layer. Indeed, the effect is of sufficient strength to exacerbate, diminish, or reverse variations that arise solely due to the reflectivity coefficient. Thus, although this attenuation is always greatest perpendicular to the crack strike, the direction of the dimming or brightening of the base reservoir event will depend upon the exact attenuation law and the crack properties. The combination of these factors contributes to a wave behavior that can provide a more adequate discrimination between conditions of brine and oil fill than an interpretation assuming the reflection coefficient alone. Unfortunately, regions of commonality do remain, and the distinction between fills is still only apparent for particular reservoir and crack conditions. The attenuated amplitudes are large enough to be seen at small offsets and may possibly account for the significant azimuthal variations in the P-wave signatures observed in field data.

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Section: Some Specific Fluid Flow Mechanismssupporting

confidence: 75%

Section: Some Specific Fluid Flow Mechanismsmentioning

confidence: 82%

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Azimuthal variation inP-wave signatures due to fluid flow

MacBeth

1999

GEOPHYSICS

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“…Pioneering theoretical work has examined P-and S-wave velocity and attenuation in TI-fractured media (Crampin, 1981(Crampin, , 1984Hudson, 1981Hudson, , 1986Thomsen, 1986;Schoenberg and Sayers, 1995). Recent attenuation studies include permeability anisotropy (Akbar et al, 1993;Gelinsky and Shapiro, 1996;Thomsen, 1995;Pointer et al, 1996). P-wave amplitude variation with azimuth and offset (AVOA) is an emerging tool for azimuthal-anisotropy studies (e.g., Strahilevitz and Gardner, 1995;Grimm and Lynn, 1997;Kühnel et al, 1997;Rüger and Tsvankin, 1997;Sayers and Ricket, 1997;Shen et al, 1997).…”

Section: Fractures and Seismic Anisotropymentioning

confidence: 99%

Detection and analysis of naturally fractured gas reservoirs: Multiazimuth seismic surveys in the Wind River basin, Wyoming

et al. 1999

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Multiazimuth binning of 3-D P-wave reflection data is a relatively simple but robust way of characterizing the spatial distribution of gas-producing natural fractures. In our survey, data were divided into two volumes by ray azimuth (approximately perpendicular and parallel (±45 • ) to the dominant fracture strike) and separately processed. Azimuthal differences or ratios of attributes provided a rough measure of anisotropy. Improved imaging was also attained in the more coherent fractureparallel volume. A neural network using azimuthally dependent velocity, reflectivity, and frequency attributes identified commercial gas wells with greater than 85% success. Furthermore, we were able to interpret the physical mechanisms of most of these correlations and so better generalize the approach. The apparent velocity anisotropy was compared to that derived from other Pand S-wave methods in an inset three-component survey. Prestack determination of the azimuthal moveout ellipse will best quantify velocity anisotropy, but simple two-or four-azimuth poststack analysis can adequately identify regions of high fracture density and gas yield.

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