f Shear-wave anisotropy in the Austin chalk from multi-offset VSP data

The Austin Chalk is an important reservoir rock, in which productivity and fluid flow directions are predominantly controlled by the presence of fractures. As part of a comprehensive study to investigate the relationship between shear-wave anisotropy and in site reservoir conditions, we have studied shear-wave VSP data from three regions in the Austin Chalk, Texas . The data come from both dry and producing wells and have been processed using currently available anisotropic estimation techniques. Comparison of data from both dry and producing wells allows us to comment on the information contained in the shear-wave signal about reservoir productivity. Analysis of the shear-wave data from these sites shows that the polarization of the leading split shear-wave at each site (and by inference the fracture direction) parallels the Austin Chalk outcrop trend, as expected from available stress measurements. Based on the results of the anisotropic estimation techniques, models have been calculated for each site showing the anisotropic seismic structure and a good match was achieved between modelled and observed anisotropic structures.