next up previous print clean
Next: Velocity errors effect Up: AVO inversion Previous: Migration effect

Velocity anomalies effect

In this case, we applied the 2-D prestack wave-equation to the synthetic data corresponding to model 2 (overburden with sinusoidal interface) using the original velocity model. We modeled and migrated the data using 1 more km on each side of the inline axis to avoid the edge artifacts at the boundary of the model, but the edge artifacts corresponding to the lateral boundaries between brine-oil and oil-tuff lithologies are still present. Figure 15 shows the picked the amplitudes at the top of the target zone in the migrated CIG. Note how the intercept and gradient change follow the sinusoidal velocity anomalies.

 
AB_var
AB_var
Figure 15
Impact of velocity anomalies in intercept and gradient attribute
view burn build edit restore

Figure 16 shows the picked amplitudes at the CIG locations, which correspond to a valley of the sinusoidal irregularities (where the event was observed to be flatter) for each lithology (positions 6.576, 7.824, and 10.304), and

 
model2migpick
Figure 16
Picked amplitudes from CIG of model 2
model2migpick
view burn build edit restore

Figure 17 shows the crossplot of the corresponding intercept and gradient attributes. In both cases, we can observe a good agreement with the expected tendencies. We also calculated the intercept and gradient attributes at CIGs locations which correspond to a peak of the sinusoidal irregularities; in this case, the relative gradient value for the shale/brine interface is higher than expected.

 
ABmodel2mig
Figure 17
Intercept versus Gradient crossplot from picked amplitudes of model 2 after migration
ABmodel2mig
view burn build edit restore


next up previous print clean
Next: Velocity errors effect Up: AVO inversion Previous: Migration effect
Stanford Exploration Project
4/28/2000