141 3. Borehole geophysical methods geothermal well shows the benefit of the acoustic method to detect stratigraphic structures observed within a potential geothermal reservoir Offset 3C VSP data can be processed to obtain PP and PS migrated VSP sections, with a very high resolution. An example of a 3C VSP obtained in the deviated section of a geothermal borehole shows the detection of a low impedance thin layer (10 m thick) which was revealed porous and productive. VSP data, recorded with both a vertical geophone and a hydrophone, allows the detection of fluid waves and flows. As example, in a reconnaissance borehole drilled to determine the geothermal parameters of geological formations, the velocity and attenuation VSP logs show a very good correspondence with respect to the lithological variations observed in the borehole and confirm the presence of flows detected by a fluid wave. Furthermore, a good correspondence between the thermal conductivity profile and the attenuation VSP logs has been noticed. The field examples show the benefit of using full waveform acoustic data and VSP, in addition to conventional and hydrogeological logs, for the characterisation of potential geothermal reservoirs. References The writing of the chapter (text and relative figures) is mainly based on the following papers and books. Archie G.E. (1942) The electrical resistivity log as an aid in determining some reservoir characteristics, Petroleum Technology 1, 55-67. Baird A., Vernier J., Goertz-Allmann B., Langet N., Rebel E., Wienecke S., Oates S. (2024) Improving the detection threshold of borehole DAS for seismic monitoring of CCS fields, paper 1367, 85th EAGE annual conference & exhibition, Oslo, Norway. Bourbiaux B., Callot J.P., Doligez B., Fleury M., Gaumet F., Guiton M., Lenormand R., Mari J.L., Pourpak H. (2007) Multi-Scale Characterization of a Heterogeneous Aquifer through the Integration of Geological, Geophysical and Flow Data: A Case Study, Oil and Gas Science and Technology, Rev IFP 62, 347-373. Boyer S., Mari J.L. (1997) Seismic surveying and well logging, Editions Technip, Paris. Chapellier D. (2001a) Aquifer logging course, from On-line course of geophysics (http://www-ig.unil.ch/). Chapellier D. (2001b) Petroleum logging course, from On-line course of geophysics (http://www-ig.unil.ch/).
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