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OMNI‐DIRECTIONAL DOWNHOLE EM PROBES *
Author(s) -
CULL J. P.,
COBCROFT R.
Publication year - 1986
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1111/j.1365-2478.1986.tb00482.x
Subject(s) - spurious relationship , geology , borehole , gemology , ellipse , regional geology , environmental geology , economic geology , polarization (electrochemistry) , electrical conductor , magnetotellurics , polarity (international relations) , polarity reversal , azimuth , remote sensing , optics , metamorphic petrology , engineering geology , computer science , physics , geometry , seismology , electrical resistivity and conductivity , voltage , mathematics , chemistry , tectonics , quantum mechanics , machine learning , volcanism , genetics , biology , geotechnical engineering , cell
Borehole surveys are usually commissioned to provide structural details as a guide to further drilling. Conductors remote from the hole are readily detected using EM probes. Vectors can be established by noting variations in wavelength, particularly for reversals of polarity. However, several holes in the same area are required to remove rotational ambiguities, and single axis systems may generate spurious anomalies related to errors in alignment. Consequently, a three‐component sensor has been designed to compare the orthogonal response at each depth. Data are expressed in terms of the invariant parameters of the polarization ellipse, and secondary fields are readily identified.