SU693312A1 - Electric geosurvey method - Google Patents

Description

(54) METHOD OF GEO-ELECTRICAL EXPLORATION

The invention relates to the field of technical physics and can be applied in geoelectrical exploration of mineral deposits of non-stationary electromagnetic fields.

There is a method of geoelectrical exploration according to the method of induced polarization (VP), in which a constant electric current is sent to the earth and after it is turned off, the potential difference decreases as time goes by.

This method has a non-permissive resolution for detecting polarizing objects.

Also known is a method of geoelectrical exploration according to the EP method, in which the electromagnetic field in the Earth is excited by single pulses or opposite-polarity pulses, and the secondary electromagnetic field is measured in a pause between them, by which the medium 2 is polarized.

Measurements using this method contain information about polarization and induction effects, the latter being a nuisance. Therefore, when searching for mineral deposits in complex geoelectrical conditions, when the desired polarizing objects are located quite deep under the cover of low-resistance sedimentary rocks and large-scale installations are used, the processes of field formation (induction effects) have a longer duration, appear polarization (polarization effects) and can not be separated, which leads to the loss of much of the information about the studied geoelectric section.

The aim of the invention is to increase the measurement accuracy by separating the polarization and induction effects during geoelectromagnetic exploration by non-stationary fields and thereby increasing the informativity of the geoelectromagnetic exploration.

Claims (2)

This goal is achieved by determining the difference of the absolute values of the signals of the secondary electromagnetic field measured by the same time interval after turning off the current pulses of different duration, according to which the magnitude of the polarization effects is judged. The essence of the method is as follows. .. Unsteady electromagnetic field in the Earth is excited by current pulses transmitted through a grounded line. First, for example, a short pulse (or several such pulses) is transmitted, and the potential difference (or voltage) of the secondary electromagnetic field is measured at the measurement points after a predetermined period of time after the current pulse has been turned off (for example, after a few milliseconds). The electromagnetic field is then excited by a longer pulse (or several such pulses) of the current, and the signal of the secondary field is measured at the same measurement points over the same period of time as in the previous case. Since for fixed conditions of excitation and measurement the process of the formation of an electromagnetic field in a conducting medium (induction effects) does not depend on the duration of the pulses of the exciting electromagnetic field, in a non-polarizing medium the difference in the absolute values of the received signals of the secondary field measured at the same time after turning on two current pulses of different duration, it is equal to zero. In polarizing media, the size of the secondary field of the EP substantially depends on the duration of the pulses of the exciting field: as the duration of the current pulses increases to a few seconds and tens of seconds, the intensity of the secondary field of the EP increases linearly, and then this growth gradually decreases. The mathematical apparatus allows one to carry out the values of the intensity of the field of EP at different durations of current passing to one specific duration. If the pulse duration is measured in units of the first tens of seconds, then we can assume that with increasing pulses. The current also increases the intensity of the secondary field of the EP. Therefore, if we measure the potential difference (voltage) of a secondary electromagnetic field at the same time interval after turning off two (or several) current pulses of different duration, this difference will be different from zero and the larger the polarized rocks are, the more polarized they will be. Thus, E + EG (1) E EG - EG, (2) where E., and Er is the intensity of the secondary field after the same period of time to after switching off the current, respectively, by pulses of duration ti and ta; EI and Ei are the stresses of the secondary field, due to the processes of becoming the field (induction effects) under the same conditions; E, and EZ. - field strength EP under the same conditions. But, as mentioned above, E., EL; Ej E | K, where K - coefficient of proportionality,. Then EZ-E; (K-1) EG, i.e., the measured potential difference (or voltage) of the secondary field does not depend on the characteristics of the field formation processes due to the conductivity of the medium, and is completely determined by polarizability. Under specific conditions of measurement, the coefficient K may be it is determined, in the general case, its value depends on the decay rate of the field of the EP and it is necessary to use a well-known analytical expression to calculate this coefficient. The coefficient K can not be determined, and the parameter measured in accordance with expression (3) should be treated in the same way as the commonly measured parameter apparent polarisability not as absolute, but as a relative parameter characterizing the polarisability of rocks measured under a certain mode. excitement sex. If the coefficient K is determined, one can also separately determine the magnitude of the induction effect and the polarization effect, which is confirmed by the analysis of expressions (1) - (3). When using the method, not only induction effects are excluded, but the natural field and self polarization of the receiving electrodes, as well as errors caused by the limited bandwidth of the receiving field sensor and the measuring channel. The invention The method of geoelectromagnetic, in which the electromagnetic field is excited by current pulses and measured in the intervals between current pulses signals of a secondary electromagnetic field, characterized in that, in order to improve measurement accuracy by separating polarization and induction effects, determine the difference between the absolute values of the secondary signals electromagnetic field, measured at the same time interval after switching on the current pulses of different duration, according to which the value of the field is judged Polarization effects. Sources of information taken into account in the examination 1. Mosquito B, A. and others. Caused by the polarization of rocks and ores and its use in electrical prospecting. Proceedings of WITS New in methods and techniques of exploration. Sat I, L., Gostoptekhizdat 1958 2. Komarov V. A. A well electo-prospecting by the method of induced polarization “Nedra, 1964, p. 85-87 (prototype)