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CONCLUSIONS

I have used marine seismic data from the Blake Outer Ridge to characterize the lateral variation of a methane hydrate reservoir. The results show that there is a strong correlation between strong BSR amplitudes and the presence of free gas underneath the hydrate. Weaker BSR reflections appear to be associated with both the absence of gas and probable decrease in amount of hydrate present. The P-impedance inversion results in strong contrasts both at the seafloor and the BSR. They are opposite in polarity because of the velocity decrease at the BSR which is partly underlain by free gas. The S-wave impedance contrast, on the other hand, shows a stronger contrast than the seafloor. Furthermore, it displays a significant amount of fracturing of the BSR and considerable contrasts from events underneath the BSR. Forward AVO modeling of CMP amplitudes at three distinct areas of the BSR result in P-wave velocity models that always show a decrease in P-velocity across the BSR, and S-wave velocities that are either increasing, decreasing or equal. At this point, I can only speculate as to what might cause these different responses in velocities and the laterally varying BSR characteristics. One possibility would be the patchy, heterogeneous distribution of hydrate and also the gas underneath. The gas underlying the BSR might occur in bubbles, trapped between small discontinuities, thus changing the elastic moduli. Furthermore, possible fracturing of the hydrate zone itself might cause part of the hydrates close to the fractures to partly destabilize due to the influx of warmer fluid. This could also affect the inferred properties.


previous up next print clean
Next: REFERENCES Up: Ecker: Hydrate Characterization Previous: AVO MODELING
Stanford Exploration Project
11/11/1997