--> Abstract: Interpreting Sand Channels From Primary And Shear Wave Seismic Inversions, by J. V. Pendrel, R. R. Stewart, and P. Van Riel; #90928 (1999).

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PENDREL, JOHN V.1, ROBERT R. STEWART2, and PAUL VAN RIEL1
1Jason Geosystems B.V., The Netherlands
2The University of Calgary, Canada

Abstract: Interpreting Sand Channels from Primary and Shear Wave Seismic Inversions

The analysis of P-wave seismic reflection data can lead to ambiguous conclusions in certain exploration situations. In principle, shear waves can provide vital additional lithologic information. In the Blackfoot area of southern Alberta, Canada, differentiation of Cretaceous channel sands and non-productive shales is problematic due to the similarity in impedance of these two lithotypes. Laboratory analysis has demonstrated that the rigidity of sand is greater than that for shale. Thus, the shear wave velocity of sand should be greater than that for shale. This implies an increase in impedance and decrease in Vp/Vs from shale to sand. The University of Calgary (CREWES Project) has recorded a seismic reflection data set wherein P-wave sources (dynamite) and three component geophones were used to record both P-P and P-S modes. We then used seismic inversion to transform the P-P and P-S reflection data to impedance. A volume estimate of Vp/Vs was made by dividing information from the two inversions.

The higher frequency P-P inversion showed good detail within the channel and clarified the complicated seismic character at and above the dominant Mississippian unconformity. Different episodes of channel deposition were identified along with a detrital layer above the Mississippian. The P-S data was lower resolution, but mapping of anomalous P-S impedance showed a striking image of the channel facies, apparently including an interesting crevasse splay feature. Agreement between the estimated Vp/Vs and available measurements from full-wave sonic logs was generally good. Importantly, new prospective areas for exploration were identified.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas