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Multi‐frequency electromagnetic method for inductive measurement of ground induced polarization and resistivity
Author(s) -
Dias Carlos Alberto,
Sato Hédison Kiuity,
Machado Marcos Vitor Barbosa,
Lima Olivar Antonio Lima
Publication year - 2019
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 - 10.1111/1365-2478.12713
Subject(s) - electromagnetic field , computational physics , magnetic field , polarization (electrochemistry) , induced polarization , isotropy , physics , electromagnetic induction , transmitter , frequency band , electrical resistivity and conductivity , electromagnetic radiation , acoustics , nuclear magnetic resonance , optics , electromagnetic coil , electrical engineering , chemistry , channel (broadcasting) , engineering , quantum mechanics , antenna (radio)
A geophysical electromagnetic method to inductively measure the ground electrical resistivity and induced polarization has recently been tested. Its basic characteristics involve three major differences from other methods: the two electrical ground parameters are obtained through measuring magnetic field. For this purpose, a transmitter–receiver (T, R) electromagnetic system is used that operates in the frequency domain and consists of a horizontal loop as the transmitter for the perpendicular loops configuration on the ground surface; the measured function is the (T, R) inductive coupling main variation produced due to the presence of the earth, that is the magnetic field radial component; the measurements are conducted at a large number of frequencies (139 in the more advanced prototype), and the measured function is explored in the frequency interval 0.2 Hz to 1 kHz, a much broader frequency range of the induced polarization effect spectrum, than the one conventionally used in field exploration. Three major aspects are emphasized: (1) the existence of a small ‘main zone’ interior to a half‐space, which is responsible for most of the magnetic energy that the receiver measures on the half‐space surface. This permits to substitute the entire half‐space by the ‘main zone’ and, in a second step, to substitute the ‘main zone’ by an equivalent homogeneous half‐space with the electrical characteristics of such ‘main zone’; (2) the existence of a closed solution for the fields that the (T, R) system generates on the surface of a homogeneous isotropic half‐space, which provides exact functions with the two electrical parameters of interest as the variables (the apparent resistivity and relative polarization parameter); (3) the values of the electrical parameters so determined can be attributed to the central point of the ‘main zone’. Three‐horizontal layers half‐space and a conductive sphere in the free‐space are discussed as models. Four field surveys are analysed as examples and show a satisfactory performance of the method for detection of on‐shore hydrocarbon reservoirs, description of induced reservoir variations and structural features mapping at depths up to 2.5 km.