Application of Enhanced Spectral Processing (ESP) to Emerging Gas Resources

摘要

Conventional Fourier spectral analysis techniques often may not have the resolution needed to evaluate thin gas reservoirs. The enhanced spectral processing used in this study eliminates windowing problems in many instances, allowing very high-resolution spectral analysis. Synthetic modeling demonstrates the high resolution of this technique by verifying the known frequency content of synthetic data. The high resolution of this technique has many potential applications in seismic exploration. We show that this technique can easily detect the change in the frequency content caused by high attenuation (Q=10-30) in a thick gas reservoir and that it can resolve the anomalous frequency response caused by tuning and the change of the frequency content caused by velocity differences between brine and gas saturated reservoir rock. We have applied enhanced spectral processing to a variety of offshore Gulf of Mexico gas reservoirs. We find that for thin gas reservoirs, the attenuation anomaly is not necessarily apparent on the timefrequency analysis. However in these cases, time-frequency analysis clearly shows the anomaly of spectral amplitude at higher frequency caused by the tuning effect. The tuning frequency can be extracted as a seismic attribute and used to detect anomalies caused by gas. We conclude that non-Fourier time-frequency enhanced spectral processing can potentially be used to directly detect and delineate hydrocarbon reservoirs due to attenuation or tuning anomalies caused by velocity differences.