Electricity: measuring and testing – Of geophysical surface or subsurface in situ – With radiant energy or nonconductive-type transmitter
Patent
1991-11-12
1993-11-09
Snow, Walter E.
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
With radiant energy or nonconductive-type transmitter
324346, 324369, G01V 328, G01V 324
Patent
active
052606619
ABSTRACT:
This invention relates to the measurement of the longitudinal components of low frequency A.C. magnetic fields from within cased boreholes which are used to measure geophysical properties of geological formations. The applied A.C. magnetic fields are generated by passing low frequency A.C. current through insulated wires or by conducting low frequency A.C. current through geological formations, either of which are examples of conducting A.C. currents through different "circuit pathways". The currents generating the applied A.C. magnetic fields are in the frequency range between 0.001 Hz and 20 Hz. The measured longitudinal components of the resulting total A.C. magnetic fields within the cased boreholes are responsive to various geophysical parameters which include the resistivities of the portions of the geological formations subject to said applied A.C. magnetic fields and to thickness variations of the casing. Calibration methods and apparatus reduce the influence of the unwanted effects due to thickness variations of the casing.
REFERENCES:
patent: 4439831 (1984-03-01), Sinclair
patent: 4748415 (1988-05-01), Vail, III
Augustin et al., "A Theoretical study of surface to borehole electromagnetic logging in cased holes" Geophysics vol. 54, No. 1 Jan. 1989 pp. 90-99.
Para Magnetic Logging, Inc.
Snow Walter E.
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