Well control

To verify the preceding observations, Figure 9 and 10 compares the $\eta$ curves with gamma ray logs available from nearby wells. Two locations are shown, one at CMP 1100, another, close by, at CMP 1220. At both locations, the Gamma ray logs indicate the presence of sands just prior to the one second mark. At this time, the $\eta$ curve also shows small values suggesting the this part of the vertical column is isotropic. Because shales induce anisotropy, more likely than not, this part of the section corresponds to sands. Figure 6 provides information from seismic data of the lateral extent of this sand layer, or layers. At CMP locations 1100 and 1220, the correlation between the well-log measurements, at a lower resolution, and the $\eta$ curve is remarkable. Recall, that the $\eta$ curve is obtained in its entirety from P-wave surface seismic data. Yet, information like the low frequency character of the shale-sand content is extracted from these data.

 

data7-gamma.well.plot
Figure 9 Left: Gamma ray logs from a well located at CMP location 1100 in Figure 4. Middle: A smoothed version of the Gamma ray measurements using a conventional box function smoother with a window 0.1 second. Right: interval $\eta$ values obtained from the seismic data for the same location.

 

data2-gamma.well.plot
Figure 10 Same as Figure 9, but for CMP location 1220. Left: Gamma ray measurements. Middle: A smoothed version of the Gamma ray measurements using a conventional box function smoother with a window 0.1 seconds. Right: interval $\eta$ values obtained from the seismic data for the same location.