Reflection moveout and parameter estimation for horizontal transverse isotropy
- Colorado School of Mines, Golden, CO (United States)
Transverse isotropy with a horizontal axis of symmetry (HTI) is the simplest azimuthally anisotropic model used to describe fractured reservoirs that contain parallel vertical cracks. Here, the author presents an exact equation for normal-moveout (NMO) velocities from horizontal reflectors valid for pure modes in HTI media with any strength of anisotropy. The azimuthally dependent P-wave NMO velocity, which can be obtained from 3-D surveys, is controlled by the principal direction of the anisotropy (crack orientation), the P-wave vertical velocity, and an effective anisotropic parameter equivalent to Thomsen`s coefficient {delta}. An important parameter of fracture systems that can be constrained by seismic data is the crack density, which is usually estimated through the shear-wave splitting coefficient {gamma}. The formalism developed here makes it possible to obtain the shear-wave splitting parameter using the NMO velocities of P and shear waves from horizontal reflectors. Furthermore, {gamma} can be estimated just from the P-wave NMO velocity in the special case of the vanishing parameter {epsilon}, corresponding to thin cracks and negligible equant porosity. Also, P-wave moveout alone is sufficient to constrain {gamma} if either dipping events are available or the velocity in the symmetry direction is known.
- Sponsoring Organization:
- Colorado School of Mines, Golden, CO (United States); USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG02-89ER14079
- OSTI ID:
- 483829
- Journal Information:
- Geophysics, Journal Name: Geophysics Journal Issue: 2 Vol. 62; ISSN GPYSA7; ISSN 0016-8033
- Country of Publication:
- United States
- Language:
- English
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