Time-lapse Shear-wave Splitting: Monitoring Hydraulic Fracturing of a Tight Gas Reservoir

The Reservoir Characterization Project at the Colorado School of Mines has collected time-lapse multi-component seismic data over a tight gas reservoir in Rulison field, Piceance basin, CO. These data are processed using a new method to localize changes of shear wave splitting in the reservoir interval. The process of shear-wave splitting is posed as an inverse problem involving instantaneous time shift calculation between shear wave modes. The time-lapse time shifts of the fast and slow shear wave modes are calculated first and then differenced. Finally, the derivative of the relative time shifts is taken to localize changes within the reservoir. The results clearly show increased shear wave splitting attributed to the presence of a massive hydraulic fracture, which was stimulated in the time-lapse interval. The azimuth of this fracture anomaly agrees with the maximum horizontal stress direction obtained through 1D well bore geomechanics.