176 Seismic Imaging The time-to-depth conversion procedure is illustrated via the line XL 217 (see location map, Figure 7.3). Ten seismic horizons, numbered 1 to 10, have been picked in time and converted to depth. The 10 seismic horizons are: 1. Top of Kimmeridgian White Limestones 2. Top of Porous Horizon HP4 3. Top of Lower Oxfordian (close to the top of target interval) 4. Top of Upper Callovian (RIO) 5. Top of Carbonated Dogger (base of target interval) 6. Base of Argillaceous limestone and marls 7. Base of Carbonated Dogger 8. Top of Domerian 9. Base of Lias (base of Gryphees limestone) 10. Top of Beaumont dolomite Figure 7.10 shows the picked times of the 10 seismic horizons (left) and the depth conversion of the 10 horizons (right). Figure 7.10 Time-to-Depth of seismic horizons by Bayesian Kriging. Example of the XL 217 profile (left: horizon in time, right: horizons in depth). To obtain a high-resolution velocity model, the acoustic impedance Ip obtained by inversion can be used assuming that the P-wave velocity and the density of a formation vary in a consistent way (an increase of velocity is associated with an increase of
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