The seismic response of the Nisku Formation in Alberta was evaluated in terms of its impedance variations with the surrounding formations. The methodology compares the effect of using a dataset processed with different approaches in an inversion study. These approaches are based on a previously conditioned dataset with a conventional processing sequence (a) versus a new specialized processing sequence (b) focused on attaining coherent noise without compromising low-frequency signal. A model-based inversion was performed with these datasets. In both cases, the inverted impedance showed good results at the well location and yielded a similar general trend and lateral variations. The inverted impedance in case b) showed a broadband result possibly related with the presence of more low frequency content in the seismic data. In case (a) the result yielded a cleaner section and the units look more continuous without much lateral variation.
A 2D seismic modelling was undertaken to simulate a CO2 injection scenario in the Nisku Formation. The time-lapse study was performed by comparing seismic amplitudes and impedance changes before and after the CO2 injection. The post-injection seismic section shows a time delay of 1.8 ms of the basal reservoir reflector and amplitude change of ~30% with respect to the baseline case. After performing the inversion, a decrease in the impedance values of ~7% is observed in the post-injection scenario.
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