Figure 13 shows the resulting amplitudes as a function of the aperture angle at CIG locations corresponding to each lithology. The aperture angle was calculated from the offset ray parameter phx using Equation (1), with and the interval velocity at the interface. We can observe some irregularities in the amplitudes values after migration. Figure 12 shows the intercept and gradient attribute calculated for each CIG. We can notice some artifacts in the data related with boundary effects; these artifacts are very strong at the edges of the model and at the lateral interfaces between the different lithologies at the target zone. Even though the CIGs used for Figure 13 were taken from locations where we noted less variability, these artifacts could be affecting the amplitudes.
Figure 14 shows the crossplot of the inverted intercept and gradient attributes for the same CIG locations used for Figure 13. The relative intercept and attribute values for the different lithologies are in good agreement with the expected tendency, however, we can note from Figure 12 that this will not be the case if the CIG's are chosen close to the boundary artifacts.
Figure 13 Picked amplitudes from CIG of model 1
Figure 14 Intercept versus Gradient crossplot from picked amplitudes of model 1 after migration