S-wave Splitting Analysis: Covariance Matrix Method and Preliminary Application

From polarization analysis on a covariance matrix, a method of S-wave splitting analysis is developed, which processes 3-component recordings simultaneously, rather than just 2 horizontal components as done traditionally. Thus not only orientation, but also dip information of fractures can be resolved. The synthetic test results show that this method is stable even for noise levels as high as 100% (S/N=1). If time window sizes are larger than roughly twice the time delay between the fast and slow S waves, the results are always reasonable even with noise levels up to 50%.The method is applied to 12 microseismic events recorded from a producing reservoir. The preliminary results suggest that stress-aligned fractures strike in NE-SW direction in the reservoir. The dips of the fractures are primarily vertical. The time difference between the fast and slow shear waves is about several tens of milliseconds per kilometer.United States. Dept. of Energy (grant DE.FC03-015F22398)Massachusetts Institute of Technology. Earth Resources Laborator