An in situ estimation of anisotropic elastic moduli for a submarine shale

Miller, Douglas E.; Leaney, Scott; Borland, William H.

doi:10.1029/94jb01849

Cited by 33 publications

(9 citation statements)

References 20 publications

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“…These are illustrated in the next section using numerical examples. described by Miller, Leaney and Borland (1994), which is similar to other shales that have been measured in situ (Costa 1993;Miller and Chapman 1991) and in the laboratory (Jones and Wang 1981;Hornby 1995 so the qP velocity near 45' is approximately equal to the vertical gP velocity, and the qSZ velocity near 45' is about 35% faster than the axial qSZ velocity. Figure 3 shows the phase slowness and group velocity surfaces for this medium.…”

Section: Velocity At 45' In Tl Mediamentioning

confidence: 77%

Velocity sensitivity in transversely isotropic media¹

Chapman

Miller

1996

Geophysical Prospecting

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Ve consider the problem of determining and predicting how the wave speeds in particular directions for a transversely isotropic (TI) medium depend on particular combinations of the density-normalized moduli A;1. The expressions for the qP and qSZ velocities are known to depend on four moduli. Normally, we can only determine three independent parameters from qP data, or two from qSZ data, as the others have much lower sensitivity. The resolvable parameters are conveniently described by axial and off-axis parameters: for qP rays, Pe. : Art, Pgo. : Ay and Pcs": (An-l Arr)14-t(Arz+2455)12; and for qSV ruys, So.: Sso. : Ass and S+s.: (AtIAz)/4-Anl2. These parameters control the magnitude of the squared-velocities on the axes and at approximately 45". F'or an arbitrary TI medium, if the medium is perturbed in a way that preserves a particular parameter, then slowness points in the associated direction and mode witl be approximately preserved in the new medium. we refer to these parameters as 'push-pins', i.e. if a parameter is fixed, the associated part of the slowness surface is pinned in place.Because, these five push-pins only contain four independent moduli, we can only fix at most three push-pins. Perturbing one of the other parameters inevitably perturbs the other. Numerical results illustrating the linkage berween two push-pins, when three are fixed, are presented.So-called anomalous TI media occur when the roles of the qlt and qsv waves are reversed: in some directions the faster ray has transverse polarization. That, in turn, requires anomalous velocities at the push-pins, i.e. Ss. ) 1r0,, S+s. ) pa5,, and,lor Sso" ) Pee" (equivalent to the usual anomalous conditions Arr I Arr, AB + A55 < 0 and/or Azz I As). In the Appendix, we confirm that anomalous sensitivities of the velocities at the five push-pins only occur in such media, although the push-pins still apply if interpreted appropriately. Truly anomalous sensitivities, in which push-pins play no role, only occur in media near the boundary between normal and anomalous.

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Section: Velocity At 45' In Tl Mediamentioning

confidence: 77%

Velocity sensitivity in transversely isotropic media¹

Chapman

Miller

1996

Geophysical Prospecting

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“…The walkaway data, preferably acquired with a five shuttle, three-component array tool, are analysed as described by Miller and Leaney (1992), through the following steps. (1) The horizontal components are projected onto a vector in the direction of the source line.…”

Section: Discussionmentioning

confidence: 99%

“…As an example, typical values for a shale are c p = 0.15 and f 4 = 0.3 (e.g. Jonesand Wang, 1981;White era/., 1983;Miller and Leaney, 1992).…”

Section: A (A N -A 55 )(A 33 -mentioning

confidence: 99%

AVO and Anisotropy from Logs and Walkaways

Leaney

1993

Exploration Geophysics

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AVO (Amplitude Versus Offset) is the seismic technique used for mapping lithology, and modelling is an important step for successful AVO interpretations. Shear velocity measurements are essential, since AVO attempts to exploit the elastic (as opposed to acoustic) nature of seismic wave propagation. A property of seismic wave propagation not often considered is anisotropy. This is probable because the magnitude of the anisotropy has been difficult to measure, and its effect on AVO is not widely known.New technology is helping to improve AVO modelling. Dipole source shear logging tools can now measure very slow shear velocities, increasing the range of applicability of AVO, and new borehole seismic techniques can measure anisotropy. When integrated, these new measurements provide more detailed information about the elastic moduli that govern wave propagation, and bring the possiblity for greater reliability in AVO interpretation.The effect of anisotropy on AVO is found to be significant and may lead to misinterpretations of AVO anomalies.

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“…Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/ Dispersion identifies TIV anisotropy has been observed in seismic (Miller et al 1994). We show calculations for Stoneley and dipole borehole propagation along the TI axis.…”

Section: Seg Houston 2009 International Exposition and Annual Meetingmentioning

confidence: 92%

Sonic dispersion curves identify TIV anisotropy in vertical wells

Valero

Ikegami

Sinha

et al. 2009

SEG Technical Program Expanded Abstracts 2009

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Sonic dispersion curves have been shown to be useful at identifying many formation behaviors, such as the type of azimuthal anisotropy when there is shear wave splitting. In this case, stress-induced anisotropy has a signature of crossing dipole dispersion curves while TIV anisotropy, when the borehole is not along the TI axis, has noncrossing or "parallel" dispersion curves. With a borehole along the TI axis, however, no shear wave splitting occurs. In this case, comparing both the dipole and Stoneley dispersion curves to dispersion curves from an equivalent Homogeneous-Isotropic (HI) formation highlights key features of the TIV formations (e.g., shales). In this paper, we highlight five points using field data from Norway, Nigeria, and the US: a) Stoneley and dipole dispersions have systematically lower slownesses (i.e., higher speeds) in TIV formations than in an equivalent HI formation, except for the dipole at zero frequency; b) the Stoneley wave slowness dispersion can even be lower (i.e., higher speeds) than the dipole dispersion at zero frequency when C66 >> C44, c) in strongly TIV formations, the shear log characteristically shows an anomalously high slowness; d) the three parameter ANNIE model is a good approximation for calculating dispersion curves for boreholes along the TI axis; and e) fitting the ANNIE model to the field data suggests that real formation can have a ratio of C66/C44 as high as 2.

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An in situ estimation of anisotropic elastic moduli for a submarine shale

Cited by 33 publications

References 20 publications

Velocity sensitivity in transversely isotropic media¹

Velocity sensitivity in transversely isotropic media¹

AVO and Anisotropy from Logs and Walkaways

Sonic dispersion curves identify TIV anisotropy in vertical wells

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An in situ estimation of anisotropic elastic moduli for a submarine shale

Cited by 33 publications

References 20 publications

Velocity sensitivity in transversely isotropic media1

Velocity sensitivity in transversely isotropic media1

AVO and Anisotropy from Logs and Walkaways

Sonic dispersion curves identify TIV anisotropy in vertical wells

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Product

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Velocity sensitivity in transversely isotropic media¹

Velocity sensitivity in transversely isotropic media¹