Time Reversal for Source Imaging

The passive seismic method for reservoir monitoring and characterisation and monitoring of hydraulically induced fractures is developing into a main stream technology in the oil business. Current techniques rely on the fact that the recorded event is detectable at most of the stations of the recording array. Weak events, not visible in the individual seismogram of the array, are missed out. We present an approach based on reversed modeling (time reversal), where no picking of events in the seismograms of the recording array is required. Assuming the correct velocity model, the reversely modelled wavefield focuses at the hypocenter of the seismic event. The origin time of the event is given by the time where maximum focusing is observed. Limitations in aperture lead to location and timing errors even for the correct velocity model. <br>These errors are below the prevailing wavelength and the signal length.