Interpretation and modelling of P-P and P-S seismic data from Lousana, Alberta

Susan L.M. Miller, Don C. Lawton and Robert R. Stewart


Two orthogonal three-component seismic lines were shot by Unocal Canada Ltd. in January, 1987, over the Nisku Lousana Field in central Alberta. The purpose of the survey was to investigate a Nisku patch reef thought to be separated from the Nisku shelf to the east by an anhydrite basin. These data have been reprocessed, analyzed, and used to develop methods for multicomponent seismic data analysis. The data are of overall good quality and major events were confidently correlated between the P-P and P-SV sections using offset synthetic seismograms. P-SV offset synthetic models were also used to extract interval Vp/Vs values from the P-SV data at well locations.

P-P and P-S isochrons were used to calculate Vp/Vs values for two intervals containing the reservoir. For both intervals, Vp/Vs was lower at two oil well locations than for the rest of the line, including a basinal well location. The decrease is attributed to the facies change from tight basinal anhydrite to porous reservoir dolomite in the Nisku Fm. This trend is in agreement with previous modelling studies.

Misties between the P-P synthetic seismogram and the P-P seismic data in the zone of interest motivated further forward modelling. The inclusion of intrabed multiples and local conversions in the offset synthetic seimograms resulted in a better tie to the data. P-P models from two wells both showed the same travel-time delay on the Nisku event.

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