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 and are currently being 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.
Forward log-based offset P-P and P-SV modelling shows character, isochron, and Vp/Vs variations associated with lithology and porosity changes between reservoir and non-reservoir rock in the Nisku. The modelling results indicate that multicomponent seismic analysis is applicable in carbonate settings, even when the reservoir intervals are relatively thin (23 m). To date, we have had difficulty applying the modelling results to this data set because of multiple contamination in the zone of interest and work is ongoing to resolve this issue. Full-waveform modelling is planned to better understand the multiple activity on both components. However, there are observable anomalies on the data which are currently under investigation.
Multicomponent recording provides additional seismic measurements of the subsurface to assist in developing an accurate geological model. Rock properties which can be extracted from elastic-wave data, such as Vp/Vs, reduce the uncertainty in predictions about mineralogy, porosity, and reservoir fluid type. Joint interpretation of P-P and P-SV data was helpful in horizon picking and in providing feedback on the validity of the interpretation. The interpretation techniques described in this paper can be usefully applied to other areas, including other carbonate plays.
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