A Glauconitic gas-bearing sandbar from Southern Alberta was studied in terms of its AVO behavior and complex attributes. The seismic data reveals an interesting anomaly in the full-offset stack. In particular, the anomaly appears clearly in the near-offset stack (0-1050 meters) but is poorly outlined in the mid-offset stack (1050-2100 meters). Subsequent AVO modelling indicates that in the subject area under study, for the Glauconitic Formation, thin-bed tuning effects overwhelm any AVO effects due to lateral changes of lithology for offsets up to 3000 meters. The differences of the anomaly as it appears in the near-offset and mid-offset stacks can be largely attributed to a lower frequency content in the mid-offset stack.
The complex attributes plots show corresponding differences of the anomaly in the various offsets attributes plots. In particular, the instantaneous frequency plot for the near offset stack reveals the anomaly distinctly, but it is virtually absent on the corresponding plot for the mid-offset stack. It is evident that complex attributes plots are very sensitive to the frequency content of the seismic data.
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