Method and apparatus for geophysical exploration in drill holes by means of very low frequency waves

Patent · Tue Oct 05 00:00:00 EDT 1976

OSTI ID:5156061

Millon, R F

A method and apparatus for geophysical exploration that does not require the installation of a low-frequency transmission source in the proximity of the drill hole are disclosed. A surface pick-up detects the magnetic field component of a low-frequency signal, which, after amplification and filtering, is supplied as one input of a comparator. A pick-up disposed in a drill hole detects the corresponding magnetic field components within the earth, and its output is supplied as the other comparator input. The amplitude ratios of the signals and their phase difference are provided at the outputs of the comparator. These values make it possible to determine the resistivity variations of the ground. The extent of the detected conductivity layer(s) may be determined by repeating the operation by using a second low-frequency transmitter positioned at a different azimuth angle from the first, and comparing the output readings. 2 figures.

• Assignee: Bureau de Recherches Geologiques et Minieres
• Patent Number(s): US 3984758
• OSTI ID: 5156061
• Resource Relation: Patent Priority Date: Priority date 14 Jun 1974, France
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
BOREHOLES
ELECTROMAGNETIC SURVEYS
EARTH CRUST
ELECTRIC CONDUCTIVITY
HZ RANGE
LOGIC CIRCUITS
RADIOWAVE RADIATION
CAVITIES
ELECTRICAL PROPERTIES
ELECTRICAL SURVEYS
ELECTROMAGNETIC RADIATION
ELECTRONIC CIRCUITS
FREQUENCY RANGE
GEOPHYSICAL SURVEYS
PHYSICAL PROPERTIES
RADIATIONS
SURVEYS
580203* - Geophysics- Geophysical Survey Methods- (1980-1989)