Seismic attributes for monitoring of a shallow heated heavy oil reservoir:A case study

In production geophysics, detecting the zones of production or constraining the in-situ conditions within a reservoir are often of greater importance than obtaining highly resolved seismic structural images. Standard seismic data processing distorts the signal and limits the potential for extracting additional information, especially for shallow targets. An alternative "sh ift-stack" procedure is applied in the processing of a shallow 12-fold, l-m common midpoint (CMP) spacing reflection profile acquired over a heated At habasca heavy oil sand reservoir. The shift-stack involves summing of CMP t races which have been flattened to an appropriate reference event. Simple m odeling confirms that the prestack waveforms are better preserved by this p rocess. Amplitude and frequency attributes are extracted from the reflectio n pro-file. Amplitudes of a continuous reservoir event vary by 600% over 35 -m intervals along the profile. Bright spots correlate with healed regions. Apparent frequencies, as measured by the instantaneous frequency and by sh ort time-window power spectral estimates of the subreservoir event are 20-3 0 Hz lower in these same regions. These diminished apparent frequencies mos t probably result from interference of the subreservoir reflection with eve nts related to structural changes within the reservoir. A complete interpre tation of the results has not been attempted as knowledge of the in-situ co nditions is incomplete. However, changes in the seismic response at the wel l locations suggest that these attributes are useful in detection and mappi ng of heated zones. The shift-stack procedure may also be useful in environ mental and geotechnical applications.