Migration effect

We applied the 2-D prestack wave-equation to the synthetic data corresponding to model 1 (overburden with flat interface) using the original velocity model and picked the amplitudes at the top of the target zone in the resulting angle domain CIG.

 

ABmodel1_var
Figure 12 Variability of intercept and gradient attribute along the different CIGs of model 1

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 p_hx using Equation (1), with $\phi=0$ and $V\left(z,m\right)=$ 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.

 

model1migpick Figure 13 Picked amplitudes from CIG of model 1

 

ABmodel1mig Figure 14 Intercept versus Gradient crossplot from picked amplitudes of model 1 after migration