116 Geophysics in Geothermal Exploration waveform acoustic logging and borehole seismic methods. We present examples of some borehole geophysical methods and applications. For more and detail information, we recommend reading specific books in well logging (Boyer and Mari, 1997; Serra and Serra, 2000; Chapellier, 2001a,b among others) and borehole seismic (Hardage, 1985, 1992; Mari et Vergniault, 2018 among others), as well as specific magazines, as “The log analyst “. 3.1 Conventional logging methods The logging tools currently run are calipers, natural radioactivity tool (natural gamma ray GR), electric resistivity and electric conductivity tools (laterologs and induction) with shallow or large depth investigation, induced radioactivity tools (neutron and density), dipmeters and acoustic tools. The logs have a vertical and horizontal resolution of several tens of cm. Well logs are recorded to identify the different geological formations crossed by a borehole. Using the response equations of logging tools and after correction for environmental effects, it is possible to obtain the physical parameters of a geological formation such as the resistivity Rt of the virgin zone, the neutron porosity ΦN, the slowness Δt (inverse of the propagation velocity), the density ρb. (a) (b) Figure 3.1 Example of logs recorded in an altered formation (after Chapellier, in Mari et al., 1999). (a) Caliper (CAL33), gamma ray (GR33), density (DENS33), Resistivity (laterolog LAT33), slowness Δt converted in velocity VIT33). (b) Comparison between core measurements and density and velocity logs after environmental corrections
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