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

Abstract 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 "shift-stack" procedure is applied in the processing of a shallow 12-fold, 1-m common midpoint (CMP) spacing reflection profile acquired over a heated Athabasca heavy oil sand reservoir. The shift-stack involves summing of CMP traces which have been flattened to an appropriate reference event. Simple modeling confirms that the prestack waveforms are better preserved by this process. Amplitude and frequency attributes are extracted from the reflection profile. Amplitudes of a continuous reservoir event vary by 600% over 35-m intervals along the profile. Bright spots correlate with heated regions. Apparent frequencies, as measured by the instantaneous frequency and by short time-window power spectral estimates of the subreservoir event are 20-30 Hz lower in these same regions. These diminished apparent frequencies most probably result from interference of the subreservoir reflection with events related to structural changes within the reservoir. A complete interpretation of the results has not been attempted as knowledge of the in-situ conditions is incomplete. However, changes in the seismic response at the well locations suggest that these attributes are useful in detection and mapping of heated zones. The shiftstack procedure may also be useful in environmental and geotechnical applications.