66 Seismic Imaging 3.1.1 Geophysical survey The acquisition procedures were optimized to obtain the best results with a high acquisition speed and a high resolution. For a seismic survey this involves high folds and wide azimuthal coverage. A three-member crew was required, working for two and a half days, to acquire: • 3D surface seismic survey, extended for about 120 × 100 m; • 2D surface seismic line, 235 m long; • Walkaway VSP, 50 m depth; • GPS surveying. The 3D surface seismic acquisition was performed using an orthogonal geometry, shot lines were perpendicular to receiver lines, with two overlapping swaths (Figure 3.2). Figure 3.2 Plan view of the survey area. 3D orthogonal geometry was used for the seismic survey, C1 shows the position of borehole. Receiver (crosses) and shot point (triangles) positions are shown. Line 3 is an additional 2D shot included in the 3D tomographic inversion. Line 1, obtained from previous data acquisition, is included for reference purposes only. Receiver lines are numbered 1 to 4. The UTM coordinate zone is 31. Adapted from Galibert et al. (2014). The main acquisition parameters are as follows: • Source: sledgehammer, with 5 m spacing, and 15 m source line spacing; • Number of shots: 154;
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