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Book Chapter

Preliminary Evaluation of Azimuthal Anisotropy Over the Valhall Field Using C-Wave Data

By
Pierre-Yves Granger
Pierre-Yves Granger
Compagnie Generate de Geophysique
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Anne Rollet
Anne Rollet
Compagnie Generate de Geophysique
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Jean-Michel Bonnot
Jean-Michel Bonnot
Compagnie Generate de Geophysique
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Published:
January 01, 2001

Abstract

A 3D-4C ocean bottom seismic data set, originally shot over the Valhall field (North Sea) to image through a gas cloud, was used to investigate the detection of azi-muthal anisotropy through the shear-wave splitting phenomenon. The data were processed in converted wave mode (C-waves), assuming that the conversion occurs at the reflection point and involves downgoing P-waves and upgoing S-waves. In this preliminary study two key horizons were used, the early-Miocene at about 2.8 seconds and the top chalk at about 5.5 seconds. The detection technique involves azimuth dependent analysis of radial-to-transverse energy ratios. Preliminary results show that the technique is capable of measuring azimuthal anisotropy effects despite a cross-spread acquisition geometry, where azimuth and offset are poorly sampled. The results show that the principal directions of anisotropy for both formations are close and coincide with the direction of the main fault system. In addition, due to the significant magnitude of the shear-wave splitting measured at the top chalk level, the converted-wave data show vastly improved resolution when oriented in fast and slow modes.

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Contents

Society of Exploration Geophysicists Open File

Anisotropy 2000: Fractures, Converted Waves, and Case Studies

L. Ikelle
L. Ikelle
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A. Gangi
A. Gangi
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Society of Exploration Geophysicists
Volume
6
ISBN electronic:
9781560801771
Publication date:
January 01, 2001

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