Detection of a thin sheet magnetic anomaly by squid-gradiometer systems: possibility of hydrofracture azimuth determination

Conference · Fri Dec 01 04:00:00 EST 1978

OSTI ID:6832096

Overton, Jr, W C

A study of the signal physics of magnetic anomaly detection was carried out by superconducting gradiometer and magnetometer loop systems with SQUID sensors for possible application to the LASL geothermal energy program. In particular, the crack produced by hydrofracture of a deep HDR geothermal borehole would be filled with a magnetic material such as ferrofluid. When polarized by the earth's field, this material would produce a localized crack magnetic anomaly which is characteristic of the azimuth of the vertical crack with respect to magnetic north. Signatures of the anomaly would be determined by taking rotation data before and after filling the crack with magnetic material. A mathematical description was found for these signatures. To test the theory and the feasibility of the idea, the deep borehole vertical cracks were simulated by using panels to define sheets 1.5 mm thick, 1.2 m wide, and 2.5 m high. When filled with ferrofluid of suitable magnetic permeability, the local anomaly develops. Signatures were measured with a horizontal axial gradiometer rotated about a vertical axis. Good agreement was found between theory and experiment for aximuths in the east and west quadrants but only fair agreement in the north and south quadrants.

• Research Organization: Los Alamos Scientific Lab., NM (USA)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 6832096
• Report Number(s): LA-UR-80-3295; CONF-8006139-1
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
150301* -- Geothermal Exploration & Exploration Technology-- Geophysical Techniques & Surveys
150900 -- Geothermal Engineering
BOREHOLES
CAVITIES
CRACKS
ELECTRONIC EQUIPMENT
EQUIPMENT
FAILURES
FLUXMETERS
FRACTURES
GEOPHYSICAL SURVEYS
GEOTHERMAL SYSTEMS
Geothermal Legacy
HOT-DRY-ROCK SYSTEMS
HYDRAULIC FRACTURES
MAGNETIC SURVEYS
MAGNETIZATION
MAGNETOMETERS
MEASURING INSTRUMENTS
MICROWAVE EQUIPMENT
POLARIZATION
SQUID DEVICES
SUPERCONDUCTING DEVICES
SURVEYS