REFERENCES

• Lumley, D. E., and Beydoun, W. B., 1991, Elastic parameter estimation by Kirchhoff prestack depth migration/inversion: Stanford Expl. Proj. Report, 70, 165-192.

• Lumley, D.E., 1992, Estimation of elastic specular reflectivity by Kirchhoff prestack depth migration: WKBJ least-squares theory: Stanford Expl. Proj. Report, 75, 355-368.

• Lumley, D.E., 1993a, Angle-dependent reflectivity estimation: Stanford Expl. Proj. Report, 77, this report.

• Lumley, D.E., 1993b, Kirchhoff prestack impedance inversion: a gas reservoir pilot study: Stanford Expl. Proj. Report, 77, this report.

 

tpow-ann
Figure 1 Raw receiver line from the 3-D coalbed methane data set. Gained by a factor of t². The coal is the bright reflection at 0.5 seconds, with a possible AVO polarity reversal at far offsets. Basement is the weak reflection at 1.3 seconds. Note the strong surface waves and aliased airwave.

 

mute-ann
Figure 2 Muted version of the raw receiver line. Note that the mute has truncated the AVO aperture on the coal reflection from about 40 degrees to about 30-35 degrees. This will have an adverse impact on ultimate shear impedance contrast resolution in the final prestack impedance inversions.

 

spectrum1
Figure 3 Raw data average spectrum before notch filter. Peak at 18 Hz is interpreted as surface wave noise .

 

spectrum2
Figure 4 Average data spectrum after 18 Hz notch filtering.

 

notch-ann
Figure 5 Receiver line data after 18 Hz notch filtering. Most of the surface wave noise has been suppressed. The aliased airwave remains. The notch also has changed the phase on the coal reflection, and eliminated the basement reflection.

 

vslan-ann
Figure 6 $\tau-p$ slant stack transform. The surface wave noise and coal reflections seem well separated in this space.

 

vstack-ann
Figure 7 NMO velocity semblance scan. The coal reflection has an rms velocity of about 4.0 km/s.

 

stack-ann
Figure 8 Receiver line stack, replicated eight times for visual effect. The coal target reflection appears at 0.5 seconds, and basement at 1.3 seconds.