Numerical and physical modelling of P-wave AVO response for fractured media

F. Fatkhan; Milovan Urosevic; John A. McDonald

doi:10.1071/ASEG2001ab040

ISSN: 2202-0586
E-ISSN:

oa Numerical and physical modelling of P-wave AVO response for fractured media
Authors F. Fatkhan^a, Milovan Urosevic^b and John A. McDonald^c
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^a Exploration GeophysicsCurtin University of Technology,, GPO Box 1987 WA, 6845, [email protected] ^b Northern Territory Geological Survey,, Darwin, [email protected] ^c Northern Territory Geological Survey,, Darwin, [email protected]
Publisher: Australian Society of Exploration Geophysicists
Source: ASEG Extended Abstracts, Volume 2001, Issue ASEG2001 - 15th Geophysical Conference, Dec 2001, p. 1 - 4
DOI: https://doi.org/10.1071/ASEG2001ab040
- Published online: 01 Dec 2001

Abstract

In this study we investigate variations of P-wave reflection coefficients with offset (AVO) and with azimuth (AVA) for a transversely isotropic medium with a horizontal axis of symmetry (HTI) in contact with water, and also with another HTI medium. Aligned, equidistant, vertical fractures, inbedded in an isotropic background, were used to represent a HTI medium. To grasp the effect of fractures their contribution was computed separately and then added to the isotropic background. The total response of a medium is then obtained by adding the two.

An approximate equation is used to compute partitioning of seismic energy at layer interfaces. The solution compares well to the results obtained in physical modelling experiments. To analyse AVO and AVA effects we used 3-D multi-azimuth transmission and reflection surveys. The results show that AVA effects are significant even at moderate angles whilst they are dominant for large incident angles. Routine 2-D AVO analysis, as commonly performed, is clearly unsuitable for HTI media.

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2001-12-01

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References

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Chang, C.H. and Gardner, G.F.H., 1997, Effects of vertically aligned subsurface fractures on seismic reflections: a physical model study: Geophysics, 62,245-252.
Crampin, S., 1984, Effective anisotropic elastic constants for wave propagation through cracked solids: Geophys. J. Roy. Astr. Soc, 76, 135-145.
Mallick, S. and Frazer, L. N., 1991, Reflection/transmission coefficients and azimuthal anisotropy in marine seismic studies: Geophysical Journal International, 105, 241- 252.
Postma, G.W., 1955, Wave propagation in a stratified medium: Geophysics, 20, 780-806.
Ruger, A., 1997, P-wave reflection coefficients for transversely isotropic models with vertical and horizontal axis of symmetry: Geophysics, 62, 713-722.
Ruger, A., 1998, Variation of P-wave reflectivity with offset and azimuth in anisotropic media: Geophysics, 63, 935-947.
Sayers, CM., and Rickett, J.E. 1997, Azimuthal variation in AVO response for fractured gas sands: Geophysical Prospecting, 45, 165-182.
Simoes-filho, I, Neves, F., Tinen, J., Protazio, J. and Costa, J., 1998, AVA modelling and inversion in fractured media: 68th Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstract, 1644-1648.
Thomsen, L., 1986, Weak elastic anisotropy : Geophysics, 51, 1954-1966.
Thomsen, L., 1993, Weak anisotropic reflection in Castagna , J.P., and Backus, M.M., Eds., Offset Dependent Reflectivity : Soc. Expl. Geophys., 103-111.
Vavrycuk, V. and Psencik, I., 1998, PP-wave reflection coefficients in weakly anisotropic elastic media: Geophysics, 63, 2129-2141.

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Article Type: Research Article

Keyword(s): Anisotropy; AVO; fractures; numerical modelling; physical modelling

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