Effects of fractures on NMO velocities and P-wave azimuthal AVO response

doi:10.1190/1.1484514

CORC > 北京大学 > 地球与空间科学学院

	Effects of fractures on NMO velocities and P-wave azimuthal AVO response
	Shen, F ; Zhu, X ; Toksoz, MN
刊名	geophysics
	2002
关键词	TRANSVERSELY ISOTROPIC MEDIA ANISOTROPIC MEDIA ELASTIC-ANISOTROPY ALIGNED CRACKS GAS SANDS SIGNATURES ROCK MOVEOUT
DOI	10.1190/1.1484514
英文摘要	This paper attempts to explain the relationships between fractured medium properties and seismic signatures and distortions induced by geology-related influences on azimuthal AVO responses. In the presence of vertically aligned fractures, the relationships between fracture parameters (fracture density, fracture aspect ratio, and saturated fluid content) and their seismic signatures are linked with rock physics models of fractured media. The P-wave seismic signatures studied in this paper include anisotropic parameters (delta((v)), epsilon((v)), and gamma((v))), NMO velocities, and azimuthal AVO responses, where delta((v))ponsible for near-vertical P-wave velocity variations, defines P-wave anisotropy, and gamma((v)) governs the degree of slicarwave splitting. The results show that in gas-saturated fractures, anisotropic parameters (delta((v)) and epsilon((v)) vary with fracture density alone. However, in water-saturated fractures delta((v)) and epsilon((v)) depend on fracture density and crack aspect ratio and are also related to V(p)/V(s) and V(p) of background rocks, respectively. Differing from delta((v)) and epsilon((c)), gamma((v)) is the parameter most related to crack density. It is insensitive to the saturated fluid content and crack aspect ratio. The P-wave NMO velocities in horizontally layered media are a function of delta((v)), and their properties are comparable with those of delta((v)). Results from 3-D finite-difference modeling show that P-wave azimuthal AVO variations do not necessarily correlate with the magnitude of fracture density. Our studies reveal that, in addition to Poisson's ratio, other elastic properties of background rocks have an effect on P-wave azimuthal AVO variations. Varying the saturated fluid content of fractures can lead to azimuthal AVO variations and may greatly change azimuthal AVO responses. For a thin fractured reservoir, a tuning effect related to seismic wavelength and reservoir thickness can result in variations in AVO gradients and in azimuthal AVO variations. Results from instantaneous frequency and instantaneous bandwidth indicate that tuning, can also lead to azimuthal variations in the rates of changes of the phase and amplitude of seismic waves. For very thin fractured reservoirs, the effect of tuning could become dominant. Our numerical results show that AVO Gradients may be significantly distorted in the presence of overburden anisotropy, which suggests that the inversion of fracture parameters based on an individual AVO response would be biased unless this influence were corrected. Though P-wave azimuthal AVO variations could be useful for fracture detection, the combination of other types of data is more beneficial than using P-wave amplitude signatures alone, especially for the quantitative characterization of a fractured reservoir.; Geochemistry & Geophysics; SCI(E); EI; 6; ARTICLE; 3; 711-726; 67
语种	英语
内容类型	期刊论文
源URL	[http://ir.pku.edu.cn/handle/20.500.11897/310942]
专题	地球与空间科学学院
推荐引用方式 GB/T 7714	Shen, F,Zhu, X,Toksoz, MN. Effects of fractures on NMO velocities and P-wave azimuthal AVO response[J]. geophysics,2002.
APA	Shen, F,Zhu, X,&Toksoz, MN.(2002).Effects of fractures on NMO velocities and P-wave azimuthal AVO response.geophysics.
MLA	Shen, F,et al."Effects of fractures on NMO velocities and P-wave azimuthal AVO response".geophysics (2002).