Microseismic Imaging using Time-reversed Wavefield Extrapolation - Synthetic Modeling and Application to a Real Data

The goals of this work are to present a source imaging technique from seismic waveforms using time-reversed wavefield extrapolation without picking the seismic first arrivals, to verify the method by imaging of synthetic data and to apply to a real data from microseismic monitoring in a geothermal field. Time-reversed wavefield extrapolation is implemented by first reversing the measured wavefields and then treating these as time-varying boundary values at the corresponding sensor positions. In the implementation, the wavefield extrapolations are performed by solving 3D acoustic wave equation with finite difference method. In each time step, wavefield envelopes are calculated. A search criteria is employed to find the location of high envelope values. The final image is created by stacking extrapolated wavefield at the corresponding time step. The source location is indicated by the brightness of accumulated wavefield envelopes. Synthetic example shows that the method works well with sparse wavefield sampling, i.e., very few receivers number. The application of the method to a real data monitoring shown an obvious indication that microseismic locations are located in a NW direction which is very similar to dominant fault trend around the area.