Effects of transverse isotropy on P-wave AVO for gas sands

Journal Article · Tue Jun 01 04:00:00 EDT 1993 · Geophysics; (United States)

OSTI ID:6103447

Kim, Ki Young ^[1]; Wrolstad, K H; Aminzadeh, F ^[2]

---

1. Korea Ocean Research and Development Inst., Seoul (Korea, Republic of). Marine Tectonics Lab.
2. Unocal Corp., Brea, CA (United States). Seismic Research and Applications Div.

Velocity anisotropy should be taken into account when analyzing the amplitude variation with offset (AVO) response of gas sands encased in shales. The anisotropic effects on the AVO of gas sands in transversely isotropic (TI) media are reviewed. Reflection coefficients in TI media are computed using a planewave formula based on ray theory. The authors present results of modeling special cases of exploration interest having positive reflectivity, near-zero reflectivity, and negative reflectivity. The AVO reflectivity in anisotropic media can be decomposed into two parts; one for isotropy and the other for anisotropy. Zero-offset reflectivity and Poisson's ratio contract are the most significant parameters for the isotropic component while the [delta] difference ([Delta][delta]) between shale and gas sand is the most important factor for the anisotropic component. For typical values of TI anisotropy in shale (positive [delta] and [var epsilon]), both [delta] difference ([Delta][delta]) and [var epsilon] difference ([Delta][var epsilon]) amplify AVO effects. For small angles on incidence, [Delta][delta] plays an important role in AVO while [Delta][var epsilon] dominates for large angles of incidence. For typical values of [delta] and [var epsilon], the effects of anisotropy in shale are: (1) a more rapid increase in AVO for Class 3 and Class 2 gas sands, (2) a more rapid decrease in AVO for Class 1 gas sands, and (3) a shift in the offset of polarity reversal for some Class 1 and Class 2 gas sands.

• OSTI ID: 6103447
• Journal Information: Geophysics; (United States), Journal Name: Geophysics; (United States) Vol. 58:6; ISSN GPYSA7; ISSN 0016-8033
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030200* -- Natural Gas-- Reserves
Geology
& Exploration
58 GEOSCIENCES
580000 -- Geosciences
ANISOTROPY
ATTENUATION
DATA ANALYSIS
FUNCTIONS
GEOLOGIC DEPOSITS
GEOPHYSICAL SURVEYS
MINERAL RESOURCES
NATURAL GAS DEPOSITS
REFLECTION
RESOURCES
RESPONSE FUNCTIONS
SEISMIC SURVEYS
SEISMIC WAVES
SURVEYS
VELOCITY
WAVE PROPAGATION