A polarization filter method and applications for preprocessing microseismic signals

The microseismic signal generated in rock rupture is wildly used in oilfields to inverse the seismic source and detect the direction and dimension of formation fractures. However, the SNR of effective signal in seismic events is especially low, and in many cases the onset of P- and S-wave is submerged in various noises. In this paper, we use the method of polarization filter to enhance wave signals in some predefined directions in order to extract P- and S-waves. This method uses the characteristics of a polarization ellipsoid which fits the particle motion to define filter parameters like rectilinearity and directionality. Combining these parameters, we get this time-varying, non-linear filter, acting as a point by point gain control to modulate the digital records. To verify the results of the method, three models have been built to inspect how the filter works at different circumstances. And the filtered waves seem to match quite well with the ideal signals of interests.