140 Geophysics in Geothermal Exploration Figure 3.21 PP-up image inverted, displayed in-depth scale. The VSP inversion predicted a porous zone below/ahead, which was confirmed by the pilot hole drilled after the VSP operation (after Naville et al., 2024a,b). Conclusion Drilling of a borehole gives geophysicists the opportunity to perform borehole geophysical measurements and record additional data. Borehole geophysical methods can be classified as conventional logging methods, borehole surface imaging methods, hydrogeological logging methods, full waveform acoustic logging and borehole seismic methods such as VSP. Borehole geophysical methods provide highresolution, localized information on rock properties like lithology, porosity, and fluid content. They also give borehole measurements used to validate and calibrate geophysical models, to convert in depth geophysical models obtained in time, to transform geophysical models into physical or petrophysical models. With full waveform data, it is possible to conduct a well micro seismic survey based on the analysis of modes reflected and diffracted on acoustic impedance discontinuities within formations or at formation boundaries. Processing of reflected modes leads to depth acoustic sections with very high resolution (a few tens of centimeters) providing an image with a depth of investigation of several meters from the well trajectory. An example of depth acoustic section obtained in a highly deviated
RkJQdWJsaXNoZXIy NjA3NzQ=