Interpretation of P-SV seismic data: Willesden Green, Alberta

Robert R. Stewart, Graham Pye, Peter W. Cary, Susan L. M. Miller

Two, crossed three-component (3-C) seismic lines and borehole seismic surveys were acquired in the Willesden Green area of central Alberta. The surveys were conducted to investigate the elastic response of a productive, fractured interval - the Second White Speckled Shale (2WS). In particular, it was proposed that fracturing in the 2WS might lead to seismic anisotropy: changes in the P- and S- wave velocities as a function of azimuth and shear-wave splitting. The borehole seismic measurements consisted of two offset vertical seismic profile (VSP) surveys, with source locations 900m north-east and 901m north-west of the well (location 8-13-41-6W5), and a zero-offset survey. Vertical vibrator sources and a wall-clamping, three-component receiver acquired high-quality VSP data over a depth interval of 400m to 2175m. The surface seismic surveys used two vertical vibrators, 3-C geophones, and receiver spreads out to 2520m offset. The lines were oriented NNW and ENE (70 degrees from each other) and were processed for P-P and P-SV reflections, including anisotropic rotations.

In this preliminary study, we find an excellent tie among the synthetic seismogram, P-wave and P-SV VSP sections, and surface seismic sections. However, there is no obvious evidence of velocity change with azimuth or shear-wave splitting.