Transversely isotropic phase velocity analysis from slowness estimates

Conference · Tue Jul 10 00:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

OSTI ID:5316026

Gaiser, J E ^[1]

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1. Univ. of Texas, Dallas (USA) ARCO Oil and Gas Company, Plano, TX (USA)

Near-offset vertical seismic profiling (VSP) is an established technique to obtain interval velocities for lithology characterization, time-to-depth calibrations, and seismic data processing. In this paper, a technique is developed for computing transversely isotropic phase velocities over intervals less than the dominant seismic wavelength. Independent estimates of vertical and horizontal slowness are made for each receiver depth and source offset pair. These provide the magnitude and direction of phase velocity for calculating the in situ elastic properties of a transversely isotropic medium. This technique requires the assumption of lateral homogeneity because horizontal slowness components are related to surface properties between sources and not to rock properties between receivers at depth. Factors that violate this assumption such as source elevation differences and dipping layers are evaluated with synthetic data. Six impulsive source P wave offset VSPs in a 663-m well in east Texas are analyzed and a near offset SH wave vibrator VSP provides vertical shear wave phase velocities. Strong transversely isotropic velocity variations observed in the Tertiary and Cretaceous sediments penetrated by this well correlate with lithology types, suggesting that this technique is sensitive to local properties at the receiver. These results may not indicate exact intrinsic elastic properties and could be due in part to dipping layers, vertical heterogeneities, and unknown local surface variations. Percent phase velocity anisotropy appears to increase from 6 to 20% for P wave and 10 to 50% for SV wave with increasing amounts of calcareous material and shale in the rock. Sandstones and chalk exhibit the least amount of anisotropy, while the shales and calcareous shales exhibit the most.

• OSTI ID: 5316026
• Report Number(s): CONF-880531--
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:B7; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ANISOTROPY
CARBONATE ROCKS
DATA PROCESSING
DETECTION
DEVELOPED COUNTRIES
ELASTICITY
FEDERAL REGION VI
GEOPHYSICAL SURVEYS
ISOTROPY
LIMESTONE
LITHOLOGY
MECHANICAL PROPERTIES
NORTH AMERICA
PROCESSING
RESERVOIR ROCK
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SEISMIC DETECTION
SEISMIC P WAVES
SEISMIC S WAVES
SEISMIC SURVEYS
SEISMIC WAVES
SHALES
SURVEYS
TENSILE PROPERTIES
TEXAS
TIME DEPENDENCE
USA
WAVE PROPAGATION
WELLS