Time-lapse VSP monitoring of steam injection

An equalization tool is designed using the time-frequency representation of a signal. It is shown that this processing helps distinguish between the foot print of the acquisition components and subsurface changes. This technique is applied to the monitoring of steam injection using walk away VSPs. A high resolution Wigner-Ville transform makes it possible to detect small changes in seismic attributes and examine the repeatability of seismic sources. It is concluded that time-frequency filtering is a particularly effective technique for removing the random components of the seismic signals, and could have the potential to eliminate the foot-print in 4-D seismic data and, hence, to extract information about changes in reservoir properties present in seismic data.