136 Well seismic surveying and acoustic logging this is combined with downhole acquisition). For a deep survey where an uncased borehole can be used, PSSL should undoubtedly be recommended. The measurement can be supplemented with full waveform acoustic logging (Sonic FWF) to improve vertical resolution with Stoneley modes. However, it remains preferable to have a data surplus in the first meters, with a downhole or crosshole, because this section is usually cased, outside of the water table, and an invasion of the formation by a sealant, which would distort PSSL measurement, cannot be excluded. Chapter 2 shows that it is possible to acquire a near-surface VSP (between 0 and 100 m), using the same means as for a downhole. After processing, the benefit of VSP is that it provides a seismic trace without multiples that is directly comparable to a surface seismic section in the vicinity of the borehole. It is important to note that the lateral investigation can be increased by offsetting the source relative to the borehole. This technique is called Offset Vertical Seismic Profiling (OVSP). The image obtained after processing is thus a single-fold seismic section. Finally, a Seismic Walkaway is a series of offset VSPs, with the surface source situated at several locations corresponding to successively increasing offsets with respect to the borehole. Therefore, the image obtained after processing is a section with a low degree of multiple-fold coverage. In addition, a VSP provides an image of the geological formations below the borehole. Chapter 3 illustrates that acoustic logging recordings with a conventional monopole probe can be used to obtain not only a P-wave velocity log, but also imaging in the well vicinity with decimetric to metric scale lateral investigation for refracted modes. In addition, the analysis of the reflected and diffracted modes with multitransmitter and multi-receiver tools makes it possible to extend the investigative power of acoustic logging and to make a micro-seismic survey of the well. The response of the Stoneley wave is strongly related to the state of continuity of the borehole wall. The attenuation of Stoneley waves (decrease of amplitude and frequency) is used to characterize the fissured medium. In addition, wave conversion phenomena are observed at the boundaries of the fractured zones. These phenomena are very pronounced on the Stoneley waves, especially in the presence of open fractures. When the shear velocity of the formation is lower than the P velocity of the borehole fluid it cannot be measured with a conventional monopole tool. It is then necessary to implement a dipole-type acoustic tool equipped with polarized transmitters and receivers. Such tools generate polarized compression waves perpendicular to the borehole axis. These compression waves create flexural modes at the well wall that generate pseudo-shear waves in the formation that propagate parallel to the well axis. The flexural wave travels at the S-wave velocity and is therefore the most reliable logging method for estimating a shear velocity log. An adaptation is available for the geotechnical field, namely PS suspension logging (PSSL) which involves a flexible tool. Using a near-surface dataset (3D seismic, VSP and full waveform acoustic logging), Chapter 4 illustrates: the principle of depth conversion of surface seismic methods using VSP data, the influence of the cementation on acoustic measurements, the principle of calibration of the formation velocity measurements obtained by
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