RU1835939C - Process of geological prospecting - Google Patents

Abstract

FIELD: electric prospecting. SUBSTANCE: process consists in excitation of pulses of current in geological section with the use of grounded perpendicular electric lines and in measurement of first and second differences of potentials with the aid of system of grounded dipole and quadrupole plants. Tensor characteristic of conductance is found by measured differences. Change of geoelectrical properties of geological section is judged by changes of elements of tensor characteristic in time. EFFECT: expanded operational use, prediction of earthquakes. 3 dwg

Description

 The invention relates to electrical exploration and can be applied in the study of changes in electrical conductivity over time at stationary observation points, in particular for earthquake prediction, environmental monitoring, etc.

 The aim of the invention is to improve the accuracy of determining changes in the geoelectric properties of the section over time by measuring the components of the electric field, their spatial derivatives and the formation of interpretation algorithms protected from local near-surface inhomogeneities.

 The goal is achieved in that the geoelectric section is sequentially excited by multidirectional electric lines. A periodic current signal is applied to the line. In observation points perpendicular installations measure the first and second potential differences or their relations. The measured values determine the elements of the matrix tensor characteristics of electrical conductivity. A change in these elements in time and space characterizes a change in geoelectric properties.

The essence of the method is as follows. In three-dimensional sections, the spatial differences of the potential are connected by linear equations of the form:
Δ ² U _x ^x (I, II, III) t _xx ^x ΔU _x + t _xy ^x Δ U _y + t _xz ^x ΔU _z
Δ ² U _y ^x (I, II, III) t _yx ^x ΔU _x + t _yy ^x ΔU _y + t _yz ^x ΔU _z
Δ ² U _z ^x (I, II, III) t _zx ^z ΔU _x + t _zy ^x ΔU _y + t _zz ^x ΔU _z
Δ ² U _x ^y (I, II, III) t _xx ^y ΔU _x + t _xy ^y Δ U _y + t _xz ^y ΔU _z
Δ ² U _y ^y (I, II, III) t _yx ^y ΔU _x + t _yy ^y ΔU _y + t _yz ^y ΔU _z
Δ ² U _z ^y (I, II, III) t _zx ^y ΔU _x + t _zy ^y ΔU _y + t _zz ^y ΔU _z
Δ ² U _x ^z (I, II, III) t _xx ^z ΔU _x + t _xy ^z ΔU _y + t _xz ^z ΔU _z
Δ ² U _y ^z (I, II, III) t _yx ^z ΔU _y + t _yy ^z ΔU _y + t _yz ^z ΔU _z
Δ ² U _z ^z (I, II, III) t _zz ^y ΔU _z + t _zy ^z ΔU _y + t _zz ^z ΔU _z , (1) where t _{xx (yx, zx)} ^{x (y, z) are the} coefficients characterizing three-dimensional geoelectric section;
I, II, III linearly independent directions in which the incision is excited;
Δ U _x , Δ U _y , Δ Y _{z the} first spatial potential differences in the directions x (y, z);
Δ ² U _{x (y, x)} ^{x (y, z) are the} second spatial potential differences in the x (y, z) direction.

 Elements t depend on the geoelectric properties of the section, the location of the observation point, and the type of excitation source. They are independent of the intensity and polarization of the source.

On the surface of the earth, where U _z 0, system (1) is simplified:
Δ ² U _x ^x (I, II) t _xx ^x ΔU _x + t _xy ^x ΔU _y
Δ ² U _y ^x (I, II) t _yx ^x ΔU _x + t _yy ^x ΔU _y (2)
Δ ² U _x ^y (I, II) t _xx ^x ΔU _x + t _xy ^y ΔU _y
Δ ² U _y ^y (I, II) t _yx ^y ΔU _x + t _yy ^y Δ U _y .

 Coefficients t characterize a three-dimensional geoelectric section and have the following properties.

 1. Protected from the action of local near-surface inhomogeneities arising near the exciting and measuring installations.

 2. Allow to judge the direction of the maximum change in the properties of the section at each measurement point.

/E_x;

/E_y
t_xx ^x; t_yx ^y; t_yy ^y. Разрез состоит из полупространства, содержащего сферу повышенного сопротивления. Моделируется профилирование установкой меньшего радиуса сферы. Модель возбуждается заземленным диполем постоянного тока, азимуты которого 0,30 и 60^о. Графики компонент электрического поля существенно зависят от поляризации источника. Гораздо более устойчивы графики отношений пространственной производной поля к напряженности. Не зависимы от поляризации источника элементы дифференциальной матрицы. В такой модели изменение поляризации возбуждающего тока может происходить из-за возникновения неоднородности вблизи источника. Неоднородность исказит значения Е и Δ Е/Е, но не действует на t.In FIG. 1 compares the stability of the determination of traditional parameters E _x and E _y and differentially-normalized parameters

/ E _x ;

/ E _y
t _xx ^x ; t _yx ^y ; t _yy ^y . The section consists of a half-space containing a sphere of increased resistance. Profiling is simulated by installing a smaller sphere radius. The model is excited by a grounded DC dipole, the azimuths of which are 0.30 and 60 ^° . The graphs of the components of the electric field substantially depend on the polarization of the source. The graphs of the relations of the spatial derivative of the field to tension are much more stable. The elements of the differential matrix are independent of the source polarization. In such a model, a change in the polarization of the exciting current can occur due to the appearance of inhomogeneity near the source. Inhomogeneity will distort the values of E and Δ E / E, but does not affect t.

 In FIG. Figure 2 shows how, using pie charts of a differential-normalized characteristic, one can determine the inhomogeneity gradients of a three-dimensional geoelectric section. The two-layer conductive model contains a protrusion of a high-resistance base, complicated by a conductive channel. The model is excited by two perpendicular grounded dipoles located on the surface and generating sinusoidal current pulses with a frequency of 0.25 Hz. The diagrams obtained from the surface of a one-dimensional two-layer section are not filled over. These are circles: the properties of the section are the same in all horizontal directions. The radius of the circles decreases with distance from the source of excitation. Charts are painted on the surface of a three-dimensional section. The direction of the maximum axes indicates the direction of maximum heterogeneity. The area of the diagrams decreases with a decrease in heterogeneity. Aside from the heterogeneity, the diagrams for the one-dimensional and three-dimensional models coincide.

Figure 3 shows a diagram of the sensors for the excitation and reception of signals on the surface of the Earth. Excitation is carried out sequentially by perpendicular electric lines II and II-II. The signal is recorded by a nine-electrode measuring device. For example, in order to use system (2), it is necessary to remove the signal Δ U _x from electrodes 4 and 6; a signal Δ U _y from electrodes 2 and 8; signal Δ ² U _x from electrodes 4-6; the signal Δ ² U _y from the electrodes 1, 7, 3 and 9.

 The method is implemented as follows.

 For the practical determination of the coefficients, for example, of system (2), it is necessary for two linearly independent positions of the source (positions I, II) to measure the first and second spatial potential differences and determine the coefficients t.

Возбуждение разреза осуществляется перпендикулярными заземленными электрическими линиями АВ размером 1-2 км. Токовые импульсы генерируются используемыми при стационарных работах источниками периодических сигналов силой в несколько сотен ампер. Используются три частоты возбуждения ω₁;ω₂= 0,1ω₁;ω₃=0,1ω₂ такие, что ω₁ в данных геоэлектрических условиях обеспечивает изучение разреза на глубину в 2-3 км.For example,
t $\genfrac{}{}{0ex}{}{\text{x}}{\text{x}}$ _x

The section is excited by perpendicular grounded electric lines AB 1-2 km in size. Current pulses are generated by sources of periodic signals with a power of several hundred amperes used in stationary work. Three excitation frequencies are used: ω ₁ ; ω ₂ = 0,1ω ₁ ; ω ₃ = 0,1ω ₂ such that ω ₁ under given geoelectric conditions provides a study of the section to a depth of 2-3 km

Areal measurements are performed. Sequentially from each of the exciting lines are recorded signals ΔU _x , ΔU _y , Δ ² U _x , Δ ² U _y .

 Stationary observation points are located taking into account the geoseismic features of the study area. Measurements are performed 4-6 times a day.

 The object of study by this method is the anomalous changes in time of the elements of the tensor characteristics of electrical conductivity, which can be caused, in particular, by changes in rock stresses preceding an earthquake; environmental changes during the injection of industrial waste; mineral extraction during the exploitation of deposits, etc.

 The interpretation parameter is anomalous (by 10 or more) changes in time and space of the coefficients t, polar diagrams of these coefficients and their frequency or spatial transformations.

 The technical and economic advantages of the proposed method compared to the known ones are that increasing the accuracy of determining changes in the geoelectric properties of the section will significantly reduce the negative consequences of geodynamic processes and environmental pollution.

Claims (1)

METHOD OF GEOELECTRIC EXPLORATION, including excitation of periodically different frequency pulses of current by a grounded electric line, measurement of the first difference in electric field potentials on the area at stationary points, by which the properties of the section are judged, characterized in that, in order to improve the accuracy of determining the change in the geoelectric properties of the section over time, additionally excite current pulses in linearly independent directions, in the indicated directions the first and second potential differences are additionally measured electric field, the measured differences determine the matrix elements of the tensor of geoelectric properties of the section, based on the system of equations:

where Δ ² v $\genfrac{}{}{0ex}{}{\text{x (y, z)}}{\text{x (y, z)}}$ (I, II, III) finite potential differences for linearly independent positions I, II, III,
t $\genfrac{}{}{0ex}{}{\text{x (y, z)}}{\text{xx (yx,}}$ _zx) coefficient characterizing a three-dimensional geoelectric discharge,
construct polar diagrams of these elements, and the geoelectric properties of the section are judged by anomalous deviations in time and space of the elements of the matrix Z and polar diagrams.

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