Moveout inversion of P-wave data for horizontal transverse isotropy
The transversely isotropic model with a horizontal symmetry axis (HTI media) has been extensively used in seismological studies of fractured reservoirs. In this paper, a parameter-estimation technique originally developed by Grechka and Tsvankin for the more general orthorhombic media is applied to horizontal transverse isotropy. The authors methodology is based on the inversion of azimuthally-dependent P-wave normal-moveout (NMO) velocities from horizontal and dipping reflectors. If the NMO velocity of a given reflection event is plotted in each azimuthal direction, it forms an ellipse determined by three combinations of medium parameters. The NMO ellipse from a horizontal reflector in HTI media can be inverted for the azimuth {beta} of the symmetry axis, the vertical velocity V{sub P0}, and the Thomsen-type anisotropic parameter {delta}{sup V}. The authors describe a technique for obtaining the remaining (for P-waves) anisotropic parameter {eta}{sup V} (or {epsilon}{sup V}) from the NMO ellipse corresponding to a dipping reflector of arbitrary azimuth. The interval parameters of vertically inhomogeneous HTI media are recovered using the generalized Dix equation that operates with NMO ellipses for horizontal and dipping events. High accuracy of the authors method is confirmed by inverting a synthetic multiazimuth P-wave data set generated by ray tracing for a layered HTI medium with depth-varying orientation of the symmetry axis. The authors show that if the medium has the orthorhombic symmetry and is sufficiently different from HTI, the best-fit HTI model cannot match the NMO ellipses for both a horizontal and a dipping event. A unique feature of the HTI model that distinguishes it from both vertical transverse isotropy and orthorhombic media is that moveout inversion provides not just zero-dip NMO velocities and anisotropic coefficients, but also the true vertical velocity. As a result, reflection P-wave data acquired over HTI formations can be used to build velocity models in depth and perform anisotropic depth processing.
- Research Organization:
- Intevep-PDVSA, Caracas (VE)
- OSTI ID:
- 20000508
- Journal Information:
- Geophysics, Journal Name: Geophysics Journal Issue: 4 Vol. 64; ISSN GPYSA7; ISSN 0016-8033
- Country of Publication:
- United States
- Language:
- English
Similar Records
Inversion of azimuthally dependent NMO velocity in transversely isotropic media with a tilted axis of symmetry
3-D moveout velocity analysis and parameter estimation for orthorhombic media