Seismic analysis was conducted to predict the orientation of the dominant fracture (cleat) system in a Cretaceous coal bed gas reservoir within the unconventional Coal Bed Methane (CBM) play in central Alberta, Canada. The extension of the method of analyzing the variation of seismic amplitude as a function of offset (AVO) to include analysis of amplitude variation as a function of azimuth (azimuthal AVO) was utilized. This technique was applied to characterize seismic azimuthal anisotropy, which indirectly predicts fracture system orientations.

The study focuses on identifying the azimuthal variation of the AVO response of the coal bed. By calculating three azimuthal AVO gradients from 2D multi-azimuth walkaway vertical seismic profiles (VSPs), the study revealed the existence of azimuthal anisotropy. A mathematical solution using these calculated AVO gradients defines the direction of the maximum change in amplitude with offset. This direction is always perpendicular to the orientation of the dominant fracture system.

The reliability of the approach used in this study demonstrates a promising method for characterizing fractures in unconventional gas reservoirs.

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