RU2210092C1 - Way of geological and electric prospecting - Google Patents

Abstract

FIELD: geological engineering survey under poor grounding conditions ( frozen soil, dry sand, solid artificial coats ). SUBSTANCE: electric field with frequency from first hundred Hz to first kHz is excited with the aid of feeding electrodes. Difference of potentials between each pair of adjacent receiving galvanocapacitive electrodes mechanically linked in measurement unit is registered and measured across output of commutation facility. Feeding and galvanocapacitive electrodes come in the form of flat metal structures abutting on examined surface with flat side. EFFECT: raised efficiency of way of geological and electric prospecting due to increase in details and speed of observation and execution of large volume of work in short time period. 2 dwg

Description

 The invention relates to electrical exploration of shallow depths and can be used to study the geoelectric heterogeneity of the upper part of the section during engineering and geological surveys in difficult grounding conditions (frozen ground, dry sands, hard artificial coatings).

 A known method of geoelectrical exploration (RU 1835939 C1, G 01 V 3/00, 06/27/1995), in which when studying the geoelectric properties of the section, the components of the electric field are measured.

 The closest in technical essence to the claimed invention is a method of mapping rocks (RU 2030768 C1, G 01 V 3/04, 03/10/1995), according to which the electric field is alternately excited by two pairs of point feed electrodes, using the receiving dipole, measure the potential difference and Based on the obtained values of the potential difference, the values of the apparent resistance are calculated, using which a geoelectric section is built.

 The disadvantage of this method is its high complexity.

 The technical result of the invention is to increase the efficiency of the method of geoelectrical exploration.

 The technical result is achieved by the fact that, in the method of geoelectrical exploration, an electric field with a frequency from the first hundreds Hz to the first kHz is excited using supply electrodes, potential differences between each pair of adjacent receiving galvanic-capacitive electrodes mechanically connected to the measuring braid are recorded and measured at the output receiving galvanic capacitive electrodes are made in the form of flattened metal structures adjacent to the test surface of one of the flat sides.

Figure 1 shows the hardware complex used when implementing the method of geoelectrical exploration:
1 - electrical prospecting current generator, with a frequency from the first hundreds of Hz to the first kHz;
2 - a device sequentially commuting to two output terminals adjacent receiving galvanic-capacitive electrodes connected to a measuring spit;
3 - electrical prospecting microvoltmeter, matched with electrical prospecting current generator;
4 - supply electrodes;
5 - receiving galvanic capacitive electrodes made in the form of flattened metal structures located on the test surface and adjacent to it on one of the flat sides, mechanically connected to a measuring braid.

 The supply electrodes and the measuring braid are fastened together with a non-conductive cord and moved along the observation profile by a drag (manually or using a vehicle). The large contact area of the electrodes with the ground (underlying surface) is their main feature. This design allows you to measure the potential difference (and sometimes the excitation of the electric field) without galvanic grounding of the receiving (and supply) electrodes.

 Often (for example, in winter), the transient resistance of the electrodes (electrode - earth) reaches MOhm. In this case, it is impossible to carry out measurements without the use of "active" electrodes. An "active" receiving electrode is a structure formed by a "passive" electrode (in this case, a metal flattened structure) and connected to it (directly at the location of the "passive electrode") by a repeater of a matching measuring device with a high input impedance (more than a Hom) and low output impedance value (first Com). Together with the meter, for each pair of receiving electrodes, the repeaters form two asymmetric measuring channels (with an asymmetric input) and one symmetric channel (with a symmetric or differential input).

 The method is as follows.

 Excitation of an electric field with a frequency from the first hundred Hz to the first kHz is carried out using an electrical exploration generator 1 and supply electrodes 4, which can be galvanic (metal pins) or galvanic-capacitive. Next, the registration and measurement of the potential difference between each pair of adjacent receiving galvanic capacitive electrodes 5 connected to a measuring spit. Electroplating electrodes 5 (or 4, 5) are made in the form of flattened metal structures located on the surface under study and adjacent to it on one of the flat sides. In the measurements, a switching device 2 is used, which in series commutates the receiving galvanic capacitive electrodes 5 to two output terminals, between which the potential difference is measured. The potential difference is recorded and measured at the output terminals of the switch using an electrical prospecting microvoltmeter 3, coordinated with the used electrical prospecting current generator 1. In total, several measurements are made, the number of which is determined by the number of receiving electrodes in the meter and the order of their switching. At the same time, when switching the receiving electrodes, the value of the effective spacing of the dipole axial electric prospecting installation ОО 'changes, which ensures the sounding effect. From the obtained values of the potential difference and the currents in the supply line, the values of the apparent resistances are calculated for different values of the active spacings of OO '.

 The entire structure is dragged (manually or using a vehicle) along the observation profile, recording and measuring potential differences at the observation points.

 Figure 2 shows an example of the application of the method of geoelectrical exploration to obtain the values of apparent resistance when conducting experimental work on the educational production base of Moscow State University. Lomonosov, in the village of Aleksandrovka, Kaluga Region.

 In FIG. 2 shows a section of the apparent resistance obtained using the proposed method of geoelectrical exploration to obtain the values of the apparent resistance using a dipole axial electrical exploration installation.

 The horizontal axis on a scale shows the distance of the pickets from the beginning of the profile, the vertical axis represents the values of the active spacing of the dipole axial electrical exploration system ОО ', the values of the apparent resistance at the observation points on the corresponding differences ОО' are shown in accordance with the given color scale. The frequency of excitation and measurement of the electric field is 625 Hz. The distance between the receiving galvanic capacitive electrodes connected to the measuring spit is 2 m. The number of receiving galvanic capacitive electrodes in the measuring spit is 8. Used galvanic capacitive supply electrodes identical to the receiving ones. Supply and receiving galvanic capacitive electrodes are made of sheet steel. The length of the supply dipole AB is 2 m. The potential difference was measured at 7 OO 'spacing values of 4, 6, 8, 10, 12, 14, and 16 m. The potential difference was converted to the apparent resistance values using the formula for direct current (" Electrical exploration ", reference book of geophysics. / Ed. By A.G. Tarkhanov. - M.: NEDRA, 1980). To excite the electric field and measure the potential difference in the receiving line, a complex of electrical prospecting equipment ERA (St. Petersburg) was used.

 The claimed method has significantly improved the efficiency of geoelectrical exploration, because when performing large volumes of work with high detail, it is sufficient to use a team of 2-3 people, while the speed of observing is 3-5 times faster than when performing work in the usual way.

Claims (1)

 The method of geoelectrical exploration, including excitation of the electric field using the supply electrodes, measuring the potential difference by the receiving electrodes and calculating the apparent resistance from the obtained data, characterized in that the electric field is excited with a frequency from the first hundreds Hz to the first kHz, the potential difference is recorded and measured at the output of the switching device between each pair of adjacent receiving galvanic-capacitive electrodes mechanically connected to a measuring spit, while the receiving galvanic-intensive tnye electrodes are in the form of flattened metal structures adjacent to the investigated surface of one of the flat sides.

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