16 Well seismic surveying and acoustic logging Table 1.1 Pros and cons of invasive and non-invasive methods. Method Target depth Vertical resolution Limitations Offshore application Non-invasive method S refraction 50 m, but sometimes less than 10 m in an industrial environment Several meters Affected by noise in an industrial environment, limited by velocity reversals Yes MASW 15 to 20 m Several meters Need for a tabular medium in the investigated area Yes AMV Several hundred meters Several meters to decameters Need for a tabular medium in the investigated area Not currently Logging Monopole sonic logging >1,000 m, for deep boreholes, of prospective exploration Several decameters Requires an uncased borehole and for Vs to be greater than Vp in the borehole fluid Yes PSSL or dipole sonic logging Up to 300 m for geotechnical deep boreholes 1 m Preferably in an uncased borehole but it’s also possible to use PSSL through a sealed case Yes, but with uncased holes Borehole seismic surveying Crosshole Up to 50 m, exceptionally 100 m 1 m Requires 2 boreholes, either uncased or with sealed casings and limited deviation Generally too expensive Downhole Up to 50 m, exceptionally 100 m, for S-waves. Can also be very deep for P-waves (> 1,000 m) Several meters Requires 1 borehole, uncased or sealed cased Yes for P-waves. Remains too complicated for S-waves Uphole 10 m for S-waves, 50 m for P-waves Several meters Difficult to have a powerful S source without damaging the casing Difficult to have an adapted S source Based on the capabilities and limitations of each method, described in Table 1.1, several choices are possible depending on the project’s objective and the level of knowledge about the site. These choices are summarized in Table 1.2. Finally, the economic aspect is also a key factor in choosing between the possible options.
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