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EIL-08 Geoelectromagnetic studies of the Earth?s crust and mantle
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Electrical exploration in 3D studies of polarizing targets
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V.S. Moiseev, Siberian Research Institute of Geology, Geophysics and Mineral Resources (Russian Federation)
N.I. Pauli, Siberian Research Institute of Geology, Geophysics and Mineral Resources (Russian Federation)
M.G. Tokareva, Siberian Research Institute of Geology, Geophysics and Mineral Resources (Russian Federation)
G.M. Trigubovich, Siberian Research Institute of Geology, Geophysics and Mineral Resources (Russian Federation)
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Multilayer bodies containing sulfide mineralizations, gold included, and being in the system of synclinal and anticlinal folds in Salair were targets of 3D studies. The layers showed higher or lower electrical resistance, but always higher polarizability.
In Kuzbas we carried out 3D studies of coal beds of increased resistance and polarizability in the same conditions. For field operations we used a central electrode spread in which a current flow electrode (CE) moved along the observation profile with another current electrode fixed far away. Electric fields were measured along the profile to the left and right of each CE station at 11 or more points of 10-20 m in spacing. The CE movement spacing was only a small portion of measuring line length.
To develop technologies of electrical exploration, we used 3D mathematical modeling in media with composite targets. According to design and field data mutually contradirectional observations and their sequential analysis of left and right measurements enabled 3D visualization of the targets. The after drilling proved the efficiency of the developed technology. For 3D studies of ore mineralization in the Sayany we used a dense network of common receiving lines with current lines varied in size. Our calculations of 3D target and subsequent drilling verified the revealed zones of higher polarization. We have also developed 3D visualization of field materials for oil prospecting. In many areas promising for oil it is found that hydrocarbons migrating over oil and gas pools change electrical resistance and polarizability of overlying or individual layers of the section. The parameter of polarizability is most informative in this case. However, whatever method you use, in the field to be measured there is, in addition to polarizability, transient field interference.
We put forward a technology which makes it possible to neutralize the transient processes at the expense of measurements by two types of spreads of middle and external gradients for common points of receiving electrodes. The recommended measurement pattern is quite practically feasible. One uses physical features of the fields to be measured, as effects of transient field and polarizability are opposite in field sign in one spread and identical in another.
The 3D mathematical modeling and field studies have essentially verified the reliability of revealed anomalies of polarizability when the compensating induced-polarization method is used. The field data gathered by multichannel measurements allow us to present our results as 3D electric fields, with a polarizing portion of the section being identified.
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