RU2581768C1 - Method for geoelectric prospecting - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to electrical prospecting by electrical resistance. Invention is primarily used in geological engineering survey; analysis of state of underground engineering objects, including hydraulic structures; mapping of geologic environment when detecting structural-tectonic irregularities; detection of ore-bearing objects, covered by loose deposits, etc. Method uses two fixed grounding connections, first of which is referred to practical "infinity" and is connected to a power source, second is placed on observation profile and is connected to a voltage meter. At equal distance from second fixed grounding connection along profile are arranged two movable grounding connections. One of movable grounding connections are connected to meter, and other to source of current and voltage drop is measured. Grounding connection, which is connected to meter, is connected to source while another movable grounding to meter and is measured again. After two measurements with one position of movable extreme grounding connections, they are moved to specified equal distance from central fixed grounding connection and measurement process is repeated. Said operations are performed at all preset positions of movable grounding connections. Then, in each point of observation for specified spacing along two measured potential difference between them, as well as average apparent electrical resistance and calculated values to the centre of apparatus (central fixed grounding connection). Calculations are performed for all separations and sections of apparent resistivity and average potential difference are constructed. According to their distribution determining presence and location in section of geoelectric irregularities.

EFFECT: technical result is improved efficiency of detection of subsurface geoelectric irregularities.

1 cl, 3 dwg

Description

The invention relates to electrical exploration by the method of electrical resistance and can improve the efficiency of studying the upper part of the geological section, identifying geoelectric heterogeneities in both near-surface and bedrock.

The area of primary application of the proposed method: engineering-geological surveys; study of the condition of soil engineering facilities, including hydraulic structures; mapping of the geological environment in the identification of structural-tectonic heterogeneities; identification of ore-bearing objects covered by loose sediments, etc.

A known method of vertical electrical sounding (VES), which uses four grounding located on the same line (observation profile). Two of them - receiving ones - are located at the same distance from the center of the installation (observation point) and are connected to the measuring device, and the other two - power supplies - are placed at the same distance from the center of the installation and connected to an electric current source. After performing measurements at one position of the supply ground, they move to the next specified distance from the installation center, etc. Based on the results of electric sensing, the values of the apparent electrical resistance of the rocks for each position of the supply ground are determined and the presence of geoelectric heterogeneities is judged by the change in the electrical resistance depending on the distance between the supply ground [1].

The known method has disadvantages: it is designed to study horizontally layered media, therefore, with the heterogeneous structure of the upper part of the section, the presence of deep non-horizontal interfaces, the ambiguity of the results of quantitative interpretation increases; experimental materials are significantly distorted with uneven terrain; the presence of a non-conductive layer in the medium makes it difficult to study lower horizons [2].

A known method of differential electrical profiling, in which the first supply ground is carried to practical infinity, and the second supply ground is placed on the observation profile and it is the center of the installation, and two receiving grounding are installed on the same line on different sides at equal distances. The three-electrode differential installation is moved along the profile with a predetermined step, and at each observation point, the supplying ground is connected to an electric current source, receivers to a measuring device, and the voltage drop between them is measured. Over a homogeneous space, the voltage drop will be equal to zero, and if there are geoelectric inhomogeneities in the section, it takes anomalous values different from zero [3].

The known method has the following disadvantage: when profiling over geoelectric heterogeneity, the anomalous voltage drop is proportional to the electrical resistance of the rocks enclosing the heterogeneities and without information about the electrical resistance of the surrounding rocks, the fixed anomaly is uncertain.

The closest in technical essence to the proposed one is a method of geoelectrical exploration, in which vertical electrical and differential sounding are combined [4]. In this method, the first supply ground is used, which is referred to practical infinity, as well as three ground connections located along the observation profile at the same distance between the extreme and central ones, of which the central one is used as the second supply ground, and the other two are receiving grounds and are used to measure the voltage drop between them, which consists in the fact that in addition to the four main earths, two additional earths are used, located along the observation profile at the same distance from the central supply ground and during each installation during operation, additional ground connections are connected either to the source of electric current and measure the voltage drop between the main fixed receiving ground or to the measuring device, and the main fixed ones are connected to the electric current source supply grounding, measure the voltage drop between the additional receiving grounding, perform the specified op radios at predetermined positions of all additional grounding, are depending voltage drop between the additional receiving ground, apparent resistivity between the main receiving ground at all positions of the supply of additional grounding and their distribution is judged on the presence and position of a sectional geoelectric inhomogeneities.

The prototype method has a drawback: when performing differential soundings, namely, measuring the voltage drop between additional groundings, the sign of the measured value over the inhomogeneity must change. DC equipment allows the sign to be measured, but with increasing separation of the receiving earthing in a differential installation, the influence of interference greatly increases. The equipment at a low frequency significantly reduces the influence of interference, but when the generator is turned on, the phase of the alternating current exciting the electric field in the medium can change arbitrarily, which leads to an erroneous determination of the sign of the measured signal.

The aim of the proposed method is to increase the efficiency of detecting geoelectric heterogeneities in the geological environment and reduce the ambiguity of the interpretation of experimental data with the heterogeneous structure of the upper part of the section.

This goal is achieved by the fact that in the proposed method of geoelectrical exploration, in which they use the first supply grounding, referred to practical infinity, as well as three groundings located along the observation profile at the same distance between the extreme and the central one, namely, that the central grounding is connected to one the terminal of the voltage meter, while one of the extreme earths is connected to the second terminal of the meter, and the other is used as the second supply ground I measure the voltage drop, then the extreme ground, which was connected to the meter, is connected to the current source, and the extreme power supply is connected to the meter and the voltage drop is measured again, after two measurements are made at the same position of the extreme ground, they are moved to a predetermined equal distance from the central grounding and the measurement process is repeated, perform the indicated operations at all given positions of the extreme grounding, then at each observation point for a given separation of two measured drops the voltage wells calculate the difference between them, as well as the average apparent electrical resistance and relate the calculated values to the center of the installation (central grounding), the calculations are performed for all spacings, sections of the apparent electrical resistance and potential difference are constructed, and the presence and location of geoelectric cross-sections are determined by sounding heterogeneities.

измеряют при использовании в качестве питающих заземлений $$(A^{/})$$

и (В).In FIG. 1 shows a diagram of the proposed installation. The signal ΔU _{MA is} measured using (A) and (B) as the supply ground. Signal $$\Delta U_{MA}{}^{/}$$

measured when used as supply ground $$(A^{/})$$

and (B).

на одной линии, причем крайние заземления (А) и $$(A^{/})$$

располагают на одинаковом расстоянии от центрального заземления (М), которое подключают к измерительному прибору. Четвертое заземление (В) относят в практическую «бесконечность» и подключают к источнику электрического тока. При выполнении измерений крайнее заземление (А) подключают ко второй клемме измерительного прибора, а заземление $$(A^{/})$$

ко второй клемме источника тока и измеряют падение напряжения ΔU_MA, затем заземления (А) подключают к источнику тока, а $$(A^{/})$$

к измерителю и измеряют падение напряжения $$\Delta U_{MA}{}^{/}$$

. После выполнения этих измерений заземления (А) и $$(A^{/})$$

перемещают на одинаковое заданное расстояние от заземления (М) и процесс измерений повторяют. Указанные операции повторяют при всех заданных положениях крайних заземлений (А) и $$(A^{/})$$

.The proposed method is carried out with electrical prospecting equipment designed for electromagnetic research methods (for example, "ERA", "ERA-V-ZNAK", "ERA-MAX" and others operating on alternating low-frequency current), as follows. Three groundings are placed on the observation profile $$(A,M,A^{/})$$

on one line, with extreme grounding (A) and $$(A^{/})$$

placed at the same distance from the central ground (M), which is connected to the measuring device. The fourth ground (B) is carried into practical “infinity” and connected to an electric current source. When performing measurements, the extreme ground (A) is connected to the second terminal of the measuring device, and the ground $$(A^{/})$$

to the second terminal of the current source and measure the voltage drop ΔU _MA , then ground (A) is connected to the current source, and $$(A^{/})$$

to the meter and measure the voltage drop $$\Delta U_{MA}{}^{/}$$

. After performing these ground measurements (A) and $$(A^{/})$$

move at the same predetermined distance from the ground (M) and repeat the measurement process. These operations are repeated for all specified positions of the extreme ground (A) and $$(A^{/})$$

.

, кажущиеся электрические сопротивления ρ_к(ΔU_MA, r), $${\text{ρ}}_{к}(\Delta U_{MA}{}^{/},\text{ r)}$$

и среднее значение

. Значения ΔU и

относят к центральному заземлению (М) и строят разрезы этих величин от разносов r=МА=МА^/. В однородном и горизонтально-слоистом полупространстве ΔU должно быть равно нулю, а над геоэлектрической неоднородностью появится аномальная разность потенциалов ΔU. По разрезу падения электрического напряжения выделяют геоэлектрические неоднородности, а по разрезу кажущегося электросопротивления классифицируют неоднородности на связанные с объектами либо пониженного, либо повышенного электрического сопротивления.From the measured voltage drops at each sensing point for each of the specified spacing (r) of the extreme grounding, the difference in voltage drops is calculated $$\Delta U=\Delta U_{MA}-\Delta U_{MA}{}^{/}$$

apparent electrical resistance ρ _to (ΔU _MA , r), $${\text{ρ}}_{\mathrm{to}}(\Delta U_{MA}{}^{/},\text{r)}$$

and average

. ΔU and

refer to the central grounding (M) and build sections of these values from the spacing r = MA = MA ^/ . In a homogeneous and horizontally layered half-space, ΔU should be equal to zero, and an anomalous potential difference ΔU will appear above the geoelectric heterogeneity. Geoelectric inhomogeneities are distinguished according to the section of electric voltage drop, and inhomogeneities are classified according to the section of apparent electrical resistance into objects of either reduced or increased electrical resistance.

, построенных от разноса r и x - местоположения пункта зондирования на профиле относительно центра шара, уверенно выделяется не только верхняя кромка неоднородности, но и ее нижняя граница (фиг. 2). На рисунке жирной линией показан контур сечения шара вертикальной плоскостью, проходящей через его центр, расположенный на заданной глубине 1,5 м. Изолиниями представлены относительные (по отношению к вмещающей среде) средние значения кажущегося электросопротивления

, а изолиния 0,8 наиболее точно описывает контур сечения шара.For the proposed method of electrical exploration, theoretical calculations of the determined parameters of electrical sounding, performed along a profile passing above the center of local heterogeneity, which was selected as a ball with 10 times higher electrical conductivity compared with the enclosing medium, showed that the apparent resistance in the section

constructed from the separation r and x — the location of the sounding point on the profile relative to the center of the ball, not only the upper edge of the inhomogeneity, but also its lower boundary, is confidently distinguished (Fig. 2). The bold line shows the contour of the cross section of the ball with a vertical plane passing through its center, located at a given depth of 1.5 m. The isolines represent the relative (relative to the enclosing medium) average values of the apparent electrical resistance

, and isoline 0.8 most accurately describes the contour of the cross section of the ball.

By way of comparison in FIG. 3 for the same model, a theoretical section of the apparent electrical resistance ρ _{k is} presented, constructed according to the well-known VES method with a symmetric four-electrode installation, where r = AB / 2 (AB is the distance between the supply ground). It can be seen from the figure that it is difficult to determine the morphology of the geoelectric heterogeneity by the nature of the isolines and to attribute the anomaly-forming object to the isometric class of forms, and its lower boundary is almost impossible to evaluate.

Thus, the advantage of the proposed method is to increase the efficiency of detecting heterogeneities of the geological environment by combining two methods of electrical sounding and more clearly identifying the boundaries of the geoelectric object with the surrounding medium in the context of electrical resistivity.

Information sources

1. Yakubovsky Yu.V. Electrical intelligence. - M .: Nedra, 1973, p. 56-57.

2. Matveev B.K. Electrical intelligence. - M .: Nedra, 1990, p. 303.

3. Tarkhov A.G. About electrical prospecting methods of pure anomaly. Proceedings of the USSR Academy of Sciences. Ser. Geophysical, 1957, No. 8, p. 981-982.

4. The method of geoelectrical exploration. Patent No. 2332690. Publ. 08/28/2008. Bull. No. 24, p. 3.

Claims (1)

The method of geoelectrical exploration, using the first supply ground connected to one of the terminals of the electric current source and assigned to practical infinity, as well as three grounds located along the observation profile at the same distance between the extreme and the central, characterized in that the central ground is connected to one meter terminal voltage, to the second terminal of the meter connect one of the extreme grounding, and the other is used as the second supply ground and measure voltage, then the extreme ground, which was connected to the meter, is connected to the current source, and the extreme power is connected to the meter and the voltage drop is measured again, after two measurements are made at the same position of the extreme ground, they are moved to a predetermined equal distance from the central ground and the measurement process repeat, perform the indicated operations at all given positions of the extreme grounding, then at each sensing point for a given separation of two measured voltage drops they calculate the difference between them, as well as the average apparent electrical resistance and relate the calculated values to the center of the installation (central grounding), perform calculations for all spacings and build sections of the average apparent electrical resistance and potential difference, according to their distribution, the presence and location of geoelectric cross-sections are judged heterogeneities.

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