Correlation between <i>P</i> -wave AVOA and <i>S</i> -wave traveltime anisotropy in a naturally fractured gas reservoir

A reservoir characterization study of Upper Green River gas reservoirs in the Bluebell-Altamont Field, in the Uinta Basin, Utah was completed in August 1995 for the U.S. Department of Energy. The study included acquisition of two crossing 2-D, 9-C seismic lines, 9-C VSP, and evaluation of the P-wave and S-wave seismic responses to the fractured reservoirs. Lynn et al. (TLE, August 1995) reported P-wave amplitude variations with offset and azimuth (AVOA) at seismic reflectors associated with fractured Upper Green River gas reservoirs in this field, and supporting observations of shear-wave birefringence in multicomponent VSPs and surface reflection seismic. This paper documents the proportional relationship observed between the difference in the P-wave AVO gradients with azimuth and the magnitude of the S-wave birefringence, estimated from the two multicomponent reflection seismic lines, evaluated at the line intersection.