Numerical modeling of shear-wave splitting and azimuthal velocity analysis in fractured media

Zimin Zhang, Donald C. Lawton, Robert R. Stewart

This report presents the processing and interpretation of seismic modeling data of the earth models for a fractured layer, based on well logs associated with potash mining. The purpose of the work is to study azimuthal seismic anisotropy, shear-wave splitting, and time-lapse seismic signals caused by vertically aligned cracks. The results show that seismic velocity anisotropy can be detected by both vertical and horizontal components of the HTI earth model; it is especially evident on radial component. Shear-wave splitting is evident and the crack orientation determined from the polarization of fast and slow shear waves is consistent with the input model. The time-shift and amplitude changes due to anisotropic layer are also apparent on both vertical and radial component data. The time-shift on radial data is up to 5ms and the amplitude change is up to 46%.

The modeled data correlate nicely with the well data. Considering the correlation results of well and surface seismic data in the previous study, this suggests that multi-component seismic data are interpretable in this potash area. This also suggests that by searching for seismic anisotropy, shear- wave splitting on the multi-component seismic data or by looking for changes in repeated seismic surveys, we may be able to detect/ monitor cracks and crack orientation in HTI model.