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Field examples of negative coincident-loop transient electromagnetic responses modeled with polarizable half-planes

Richard S. Smith and G. F. West
Field examples of negative coincident-loop transient electromagnetic responses modeled with polarizable half-planes
Geophysics (November 1989) 54 (11): 1491-1498

Abstract

The negative transients observed in coincident-loop measurements are believed to be caused by polarizable conductive structures (i.e., structures whose in-phase conductivity increases with frequency). For most structures, it is not possible to predict negative transients as large as some of those observed in the field unless the polarizability is exceptionally large. Previous work shows that modest polarizabilities can be used to predict negative transients of the correct magnitudes when the conducting structures are such that the following qualitative conditions apply: (1) the transmitter is positioned proximal to the conducting structure in a manner which ensures a large early-time fundamental inductive current is induced in the structure; (2) the polarization current is proximal to the receiver and results in a measurable negative polarization response; and (3) the positive response associated with the fundamental inductive current decays away sufficiently rapidly that the total response can change sign. These conditions are termed the 'favorable coupling conditions.' A polarizable half-plane model is a structure which satisfies these conditions. The positions near the edge of the half-plane, where the favorable coupling conditions are best satisfied, are those which are most conducive to observing negative transients. Field examples of negative transients associated with either an overburden which comes to an edge or a dipping sheet-like structure can be modeled with a weakly polarizable half-plane. We believe that most of the negative transients observed in the field are likely to be associated with structures which satisfy the favorable coupling conditions.


ISSN: 0016-8033
EISSN: 1942-2156
Coden: GPYSA7
Serial Title: Geophysics
Serial Volume: 54
Serial Issue: 11
Title: Field examples of negative coincident-loop transient electromagnetic responses modeled with polarizable half-planes
Affiliation: Univ. Toronto, Dep. Phys., Geophys. Lab., Toronto, ON, Canada
Pages: 1491-1498
Published: 198911
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 36
Accession Number: 1990-005161
Categories: Applied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Presented at the Aust. Soc. Explor. Geophys./Soc. Explor. Geophys., Int. Geophys. conf. and exhibit., Adelaide, South Aust. Feb. 14-21, 1988
Illustration Description: illus.
S35°00'00" - S14°00'00", E113°00'00" - E129°00'00"
S37°30'00" - S28°15'00", E141°00'00" - E153°30'00"
N07°00'00" - N37°00'00", E68°00'00" - E97°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 1990
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