Joint inversion of P- and PS-waves in orthorhombic media: Theory and a physical modeling study
- Colorado School of Mines, Golden, CO (United States). Center for Wave Phenomena
- Science Research Lab., Somerville, MA (United States)
Reflection traveltimes recorded over azimuthally anisotropic fractured media can provide valuable information for reservoir characterization. Normal moveout (NMO) velocity of any pure (unconverted) mode depends on only three medium parameters and usually has an elliptical shape in the horizontal plane. Because of the limited information contained in the NMO ellipse of P-waves, it is advantageous to use moveout velocities of shear or converted modes in attempts to resolve the coefficients of realistic orthorhombic or lower-symmetry fractured models. Joint inversion of P and PS traveltimes is especially attractive because it does not require shear-wave excitation. Here, the authors show that for models composed of horizontal layers with a horizontal symmetry plane, the traveltime of converted waves is reciprocal with respect to the source and receiver positions (i.e., it remains the same if they interchange the source and receiver) and can be adequately described by NMO velocity on conventional-length spreads. The azimuthal dependence of converted-wave NMO velocity has the same form as for pure modes but requires the spatial derivatives of two-way traveltime for its determination. Using the generalized Dix equation of Grechka, Tsvankin, and Cohen, they derive a simple relationship between the NMO ellipses of pure and converted waves that provides a basis for obtaining shear-wave information from P and PS data. The method is applied to a physical modeling data set acquired over a block of orthorhombic material -- Phenolite XX-324.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- OSTI ID:
- 329237
- Journal Information:
- Geophysics, Journal Name: Geophysics Journal Issue: 1 Vol. 64; ISSN GPYSA7; ISSN 0016-8033
- Country of Publication:
- United States
- Language:
- English
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