Anisotropy and AVO from walkaways

Conference · Sat Dec 31 04:00:00 EST 1994

OSTI ID:80179

Leaney, W S ^[1]

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1. Schlumberger Interpretation Development, Jakarta (Indonesia)

A multi-offset VSP or ``walkaway`` is a wide aperture borehole seismic experiment ideal for studying angle-dependent wave propagation. In this paper, two aspects of elastic wave propagation are studied with walkaways: anisotropy (transverse isotropy) and AVO (amplitude variation with offset). Anisotropy is measured from walkaway data using extracted vertical and horizontal phase slownesses. Results are shown for a Java Sea walkaway data set and tabulated for walkaways from different locations. The anisotropy measurements are classified using Schoenberg`s parameters of ellipticity and anellipticity. Shale anisotropy is found to be significant and variable. Anisotropic AVO is studied on Ostrander`s shale-sand model and through the computation of anisotropic ray-trace synthetics. The ratio of ellipticity to anellipticity is found to be a good measure of shale anisotropy in the context of AVO. Depending on the ``flavor`` of shale anisotropy, AVO can be significantly reduced or exaggerated. The AVO response of a reservoir sequence can also be measured (as opposed to modeled) with a properly designed walkaway. The results of processing a walkaway for AVO are shown. Such a seismic experiment is arguably the best way to determine the AVO response of a reservoir or reservoir sequence. Together, these two new applications of walkaways -- to measure anisotropy and AVO -- can be used to: (1) Establish the viability of using AVO to map a reservoir. (2) Reduce the risk involved with the added cost of AVO studies. (3) Improve the reliability of AVO interpretations.

• OSTI ID: 80179
• Report Number(s): CONF-941015--
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
03 NATURAL GAS
58 GEOSCIENCES
ANISOTROPY
DATA PROCESSING
GEOLOGIC DEPOSITS
NATURAL GAS INDUSTRY
PETROLEUM INDUSTRY
RESPONSE FUNCTIONS
SEISMIC SURVEYS
SEISMIC WAVES
WAVE PROPAGATION