Paper 20

1. ) Using existing water wells for lithologic investigation: Casing conditions allow only a very constricted measuring program. Natural gamma and induction log (PVC cased) give lithological information about the profile under consideration of the completion material (gravel clay barrier etc.). On this basis a simplified geological profile in an alpine valley was reconstructed.
2. ) Investigation of the hydraulic function of water wells: After completion or after years of production the hydraulic constitution of the well is of interest; in some cases the productivity decreases. A combination of methods is used for a hydraulic diagnosis:
   • Gamma- and Gamma-Gamma-Density gives a picture of lithology and completion properties. Such completion properties are, for example, any clay content in the screened parts or "bridges" in the gravel pack.
   • With a flowmeter with a "packer disc" the hydraulic function (permeability) of the system screen + gravel pack can be controlled. Measurements with an additional pump allow a quantitative characterization of the hydraulic profile. The examples demonstrate various applications of detection (intact screens, screens with clay colmation, gravel pack defects) and are compared with borehole-TV records.
   In one case logs were measured before and after completion. Log documentation and comparison can be used as a "quality passport for the well".
3. ) Old water wells:
   In some parts of Austria artesian water wells for farmers have been working for more than 50 years. Log measurements give an information about the producing aquifer and well construction. Results help in case of defects or decreasing productivity. This is demonstrated for a more-than-100-year-old water well. Summarizing, geophysical well log measurements in existing water wells
   • give a lithological information particularly if there are no exploration wells in this area,
   • are practical instruments for a hydraulic and technical diagnostic of producing wells

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