Conclusions

Many existing time-lapse seismic image registration algorithms are designed to measure timeshifts in the absense of amplitude changes between images. These algorithms may produce spurious timeshifts associated with amplitude changes at the reservoir level. Amplitude changes are not only connected to changes in rock properties due to fluid production and/or injection, but may also be caused by tuning effects associated with low frequencies and/or thin beds. We propose to evalulate the frequency depedence of 4D timeshift estimation using the local time-frequency transform. Timeshifts in the presense of amplitude changes are estimated using amplitude-adjusted plane-wave destruction filters at each frequency. The impact of sidelobe interference is minimized at high frequencies. This algorithm partially alleviates the spurious timeshift problem and provides a more reliable estimate of 4D timeshifts.