80 Seismic Imaging 3.3.1.4 Depth elastic images and general discussion The diffraction tomography provided an estimation of the elastic parameters, P and S-wave velocities, and density, as illustrated in Figure 3.13. These results enabled the identification of several interesting features that were interpreted as: • the top of the Brent reservoir, which can be delineated and described continuously away from the borehole; • tilted panels under the Cretaceous base discordance - Cimmerian unconformity, at depth of 3,558 m. • a reverse fault at 250 m east of the borehole, with an apparent throw < 30 m, unclear whether it reaches the reservoir; • a normal fault about 450 m east of the borehole with an apparent throw ≈ 60 m, intersects the reservoir at about 350 m offset; • an event at depth ≈ 3,850 m, slightly dipping to the west, which was interpreted to be the Heather sandy claystone formation. Figure 3.13 Elastic depth images (P and S-wave velocities and density) of VSP field data of Figure 3.12. The initial input model is at the left of each image. The Brent reservoir and two fault locations were successfully interpreted. Adapted from Beydoun et al. (1990). The quality control of the elastic depth images is given by the goodness of fit between synthetic and field data sets. Therefore, Figure 3.14 illustrates the synthetic
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