57 2. Refraction surveying map. The average velocity V1 in the weathering zone is computed from the velocity distribution obtained by the inversion procedure in the 0-H depth interval. The V2 velocity of the refractor is computed from the velocity distribution obtained by inversion in a narrow depth bandwidth (3 m) situated below the interface located at the depth H. The application to the 3D data is shown in Figure 2.17. a b c d Figure 2.17 3D static corrections from 3D tomographic inversion. (a) Thickness H of the weathering zone. (b) Average velocity V1 in the weathering zone. (c) Velocity V2 below the weathering zone. (d) 3D static correction map (-H/V1 + H/V2). The picked times of the refracted waves were able to provide both a map of the reservoir top (using the T plus –T minus method) and a map of the shape index. Figure 2.18 shows an example of a shot point oriented in the in-line direction before and after the filtering of direct and surface waves. After filtering, a refracted wave is clearly visible, along with interference from refracted – reflected events.
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