Determining electrical conductivity of an earth layer

Details Determining electrical conductivity of an earth layer Determining electrical conductivity of an earth layer

1995-12-01

1998-02-24

O'Shea, Sandra L.

Electricity: measuring and testing

Of geophysical surface or subsurface in situ

With radiant energy or nonconductive-type transmitter

G01V 310

Patent

active

057214913

ABSTRACT:
A method is provided for determining an electric conductivity of an earth formation formed of different earth layers, whereby a wellbore containing a wellbore fluid extends through said formation. The method includes lowering an induction logging tool into the wellbore to a location surrounded by a selected one of the earth layers, the tool including a magnetic field transmitter suitable to induce magnetic fields of different frequencies in said earth layers, and magnetic field receiver suitable to receive response magnetic fields at different spacings from the transmitter and to provide a signal representative of each response magnetic field. At least two of the different frequencies and at least two of the different spacings are selected, and for different combinations of each selected frequency and each selected spacing, the transmitter is operated so as to induce a magnetic field of the selected frequency in said earth layers, which magnetic field induces a corresponding response magnetic field near the tool. The receiver is operated at the selected spacing from the transmitter so as to provide a signal representing the response magnetic field. The signals are combined in a manner so as to create a combined signal having a reduced dependency on the electric conductivity in the wellbore region and the electric conductivity of an earth layer adjacent the selected layer.

REFERENCES:
patent: 3259837 (1966-07-01), Oshry
patent: 3893021 (1975-07-01), Meador et al.
Tabarovskii et al., 1979, "Radial Characteristics of Induction Focusing Probes with Transverse Detectors in an Anisotropic Medium," Soviet Geology and Geophysics, 20, pp. 81-90.

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