250 Geophysics in Geothermal Exploration Figure 8.7 Shifts detected in milliseconds (left) converted to interval velocity (right) for an azimuthal sector. Some observations can be made: • The shifts detected are different from one azimuthal sector to another, already revealing VVAZ effects. • The shift main shift changes (except the shallow weather zone) are located at the Top Cretaceous level. In the end, the procedure to derive interval velocities from the shift volume has been applied to the 6 azimuthal stacks, ready to extract the VVAZ anisotropy. 8.6.2 Model-based inversions The azimuthal stacks have been aligned using the detected optimal shifts to optimize their mutual compatibility, for estimating properly the AVAZ effects. Then, to obtain P-impedance model by sector, a series of model-based seismic inversions is performed. To illustrate, an optimized impedance section, for one sector, is proposed Figure 8.8. Figure 8.8 P-impedance section from the prior model (left) and after inversion for stack 1 (right).
RkJQdWJsaXNoZXIy NjA3NzQ=