3-D description of normal moveout in anisotropic inhomogeneous media
- Colorado School of Mines, Golden, CO (United States). Center for Wave Phenomena
The authors present a new equation for normal-moveout (NMO) velocity that describes azimuthally dependent reflection traveltimes of pure modes from both horizontal and dipping reflectors in arbitrary anisotropic inhomogeneous media. For homogeneous transversely isotropic media with a vertical axis of symmetry (VTI media), the equation for azimuthally dependent NMO velocity from dipping reflectors becomes a relatively simple function of phase velocity and its derivatives. The authors show that the zero-dip NMO velocity V{sub nmo}(0) and the anisotropic coefficient {eta} are sufficient to describe the P-wave NMO velocity for any orientation of the CMP line with respect to the dip plane of the reflector. Using the formalism, V{sub nmo}(0) and {eta} (the only parameters needed for time processing) can be found from the dip-dependent NMO velocity at any azimuth or, alternatively, from the azimuthally dependent NMO for a single dipping reflector. The authors also apply this theory to more complicated azimuthally anisotropic models with the orthorhombic symmetry used to describe fractured reservoirs. For reflections from horizontal interfaces in orthorhombic media, the axes of the normal moveout ellipse are aligned with the vertical symmetry planes. Therefore, azimuthal P-wave moveout measurements can be inverted for the orientation of the symmetry planes (typically determined by the fraction direction) and the NMO velocities within them. If the vertical velocity is known, symmetry-plane NMO velocities make it possible to estimate two anisotropic parameters equivalent to Thomsen`s coefficient {delta} for transversely isotropic media.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- OSTI ID:
- 619628
- Journal Information:
- Geophysics, Journal Name: Geophysics Journal Issue: 3 Vol. 63; ISSN GPYSA7; ISSN 0016-8033
- Country of Publication:
- United States
- Language:
- English
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