89 5. Geophysical methods 5.1 Seismic and acoustic methods The 3D survey was designed to obtain a 3D block based on records of low amounts of data [1, 2, 3]. The complete survey is composed of 20 receiver lines (the in-line direction) with a 15 m lag distance between adjacent lines (Fig. 2a), each line being composed of 48 single geophones with 5 m spacing between adjacent geophones. For each receiver line investigated, direct and reverse shots (source in line with the receiver line) were recorded (Fig. 2b top), as well as crossline shots fired at distances of 40, 50, and 60 m perpendicular to the receiver line (Fig. 2b bottom). Processing the data from in-line direct and reverse shots gathers the results in a vertical section of 240 m in-line extension (the blue arrow, in a b c d Figure 2 Seismic spreads and field implementation of seismic lines. Modified after Mari et al. 2008 and 2011. (a) Seismic line implementation: the distance between two adjacent lines is 15 m; red points indicate well locations. (b) Seismic spreads: A direct shot and a reverse shot are fired in line to obtain 2D seismic images (top). Several shots are fired cross-line to obtain 3D seismic images (bottom). (c) Example of in-line shot gather, d) Example of cross-line shot gather with 60 m of lateral offset.
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