Method of soil resistivity time variations measurement

FIELD: physics.

SUBSTANCE: current is cutoff to soil through two point sources. The first source is placed close by vertical interface, and the second is taken to infinity. Position of one equipotential line of electric field is detected. Measuring electrodes is mounted by tangent to equipotential line symmetrically to tangency point of ray lined from auxiliary point presenting mirror reflection of point source relative to interface with specified equipotential. Besides, measuring electrodes can be placed by line, perpendicular to interface symmetrically to power supply provided close by interface. Near to interface there is compensatory point source with current value fixed by parity where I0, Ik are currents from the first and compensatory sources, ΔΨ1MN is differential of the space function that determinates position of measuring electrodes relative to the first source, ΔΨ2MN is differential of space function that determinates position of measuring electrodes relative to compensatory source. Measuring electrodes voltage indicates time variations of resistivity.

EFFECT: simplified positioning of electrical survey unit and improved measurement accuracy.

1 dwg

 

The invention relates to the technical physics and is intended for control of geodynamic changes in learning environments and geological objects.

There is a method of measuring temporal variations of the resistivity of the Earth, namely, that miss in the Ground current through the two point source. One source have a near vertical boundary between two different resistance environments. Thus determine the position of one of the equipotential lines of the electric field and the change of potential difference measuring electrodes located on this line, register variations of resistance [1].

The disadvantage of the proposed method is the low accuracy of the measurement of the resistivity of the Earth in the absence of massive ores, due to the fact that signals when transmitting pulses of different polarities differ from each other only if the emitted object has a high surface polarization. At the same time when solving problems of control of geodynamic changes of geological objects, the ionic conductivity of the media is the determining factor, and the polarizability of the environments has a low value. As a consequence, the value of register variation is caused not only by changes in the physical environment, which directly caused her geodynamics, but the change of temperature and humidity on the surface environment (pobegoobrazuyuschaya factors).

Closest to the proposed method is a way of measuring the variations of the resistivity of the Earth [2], namely, that miss in the Ground current through the two point source. The first source have a near vertical boundary between two different impedance environments, determine the position of one of the equipotential lines of the electric field and the change of potential difference measuring electrodes located on this line, record temporal variations of resistivity. Thus, the measuring electrodes are placed along the tangent to the equipotential lines of the electric field created, symmetrically relative to the edges touch a ray drawn from the auxiliary point representing the mirroring point source relative to the boundary, with the selected equipotential. Also, the measuring electrodes may be located on a line perpendicular to the boundary, symmetrically with respect to the supply source, which is located near the border.

Disadvantages of the proposed method is the difficulty in precisely measuring electrodes on the proposed methodology and therefore less sensitivity to small geodynamic changes in the studied geological objects. So as to ensure that t is Buemi measurement accuracy it is necessary to achieve maximum signal to noise ratio. This is possible only with a very precise setting of the measuring electrodes on the equipotential lines. In addition, due to geodynamic changes of the studied geological objects equipotential lines, as a rule, are shifted to achieve the required measurement accuracy is required to reinstall the measuring electrodes that difficult, and in Geomonitoring measuring systems is impossible.

The purpose of the invention is the improvement of measurement accuracy and simplify the positioning of electrical installation.

This objective is achieved in that, in accordance with the method of measuring temporal variations of the resistivity of the Earth through the Ground current through the two point source, the first of which have near vertical boundary between two different impedance environments, determine the position of one of the equipotential lines of the electric field, the measuring electrodes have on the tangent to the equipotential lines of the electric field created, symmetrically relative to the edges touch a ray drawn from the auxiliary point representing a mirror reflection of the point source relative to the boundaries of the partition with the selected equipotential or measuring electrodes are placed on a line perpendicular to the boundary, with metecno relative to the supply source, located near the border, added compensation point source, which is located near the boundary line.

The drawing shows a diagram illustrating the proposed method.

The scheme includes two media 1 (with a specific resistance ρ1and ρ2), point source 2 (A), the second point source (In) conditionally assigned to infinity, a dummy source 3, the selected equipotential 4, the measuring electrode 5 and the compensating source 6.

The proposed method is implemented as follows.

The electrical profiling to find the location of the vertical boundary between two different impedance environments 1. At a distance d from the boundary set one point of the current source 2 and the second point source is attributed to infinity (distance >10d). Compensation source 6 come close to the first. Base distance d determined on the basis of power installations and peculiarities of the geological structure of the area.

The placement of the measuring electrode 5 is performed by the following procedure: determine the position of the auxiliary point 3 on the line of the perpendicular drawn from the point of location of the first source section two environments representing its mirror reflection razdelyut one of the equipotential lines 4 and on the contact line of the beam, conducted from the auxiliary point, and equipotential lines include measuring electrodes symmetrically touch points. It is also possible to place the measuring electrodes symmetrically with respect to the supply source on a line perpendicular to the section of the two environments. The presence of a compensation point source 6 can compensate for how inaccurate positioning of the electrical installation carried out by the method and geodynamic changes of the studied geological object, without having to reinstall the system.

The essence of the proposed method is as follows: the voltage on the measuring electrodes can be represented as the sum of the useful signal Up(t), which arise from temporary variations in the properties of the medium, and the signal generated by the compensation source Ukand additive noise U0.

Us(t)=Up(t)+U0+Uk.

Additive interference is determined by the initial installation of the electrodes and slow geodynamic changes in the object and can be neutralized by the compensation signal source. Thus the achievable measurement accuracy is determined by the ratio of useful signal to noise ratio, is determined only by the sensitivity of the applied geoelectric measurement system and the stability of the sources used.

the Ust has medium with a vertical border of section 1, with specific resistances ρ1and ρ2. In this case, the additive noise voltage and the voltage generated by the compensating source [3]

U0=I0ΔΨ1MN(x,y), Uk=IkΔΨ2MN(x,y),

where ΔΨ1MNthe differential spatial function, which determines the position of the measuring electrodes on the equipotential line according to the first source (the exact setting it equal to zero),

ΔΨ2MNthe differential spatial function, which determines the position of the measuring electrodes relative to the compensation source,

I0, Ik- currents of the main and compensating source.

Differential spatial functions is calculated as the difference between the spatial functions that determine the position of the measuring electrodes relative to the primary or compensatory source ΔΨMN(x,y)=ΨM(x,y)-ΨN(x,y). Spatial functions can be defined based on known solutions to electrical problems.

For example, for the two environments, the potential of a point source is defined by the following relation [4]:

In this case, spatial functions have the form:

They are spatial, depending only on the relative coordinates of the source and recording points of the field, as well as the spatial position of the partition. The environmental settings are included in this ratio as constants.

In accordance with these ratios, it is seen that the selection of the current value of the compensation source, you can eliminate the influence of additive noise. The current value can be defined as follows

The proposed method allows to simplify the positioning of the electrical installation and to improve the measurement accuracy of small temporal variations of the resistivity of the Earth. Its application makes it easy to conduct operational configuration of electrical installation with long-term measurements and determine accordingly minor geodynamic changes to the object by increasing the sensitivity.

Sources of information

1. USSR author's certificate No. 301661, CL G01V 3/02, 1971.

2. USSR author's certificate No. 1048439, CL G01V 3/02, published 15.10.83. Bull. No. 38 (prototype).

3. The electrical method of resistance. Ed. Achmelvich and Vaseline: Textbook. the allowance. - M.: Moscow state University press, 1994.

4. Zaborovsky A.I. Electromagnetics. - M.: Publishing house of the Oil and mining of fuel and literature. 1943.

The method measured the I temporal variations of the resistivity of the earth, namely, that miss in the ground current through the two point source, the first of which have near vertical boundary between two different impedance environments, and the second refers to infinity, determine the position of one of the equipotential lines of the electric field, the measuring electrodes have on the tangent to the equipotential lines of the electric field created, symmetrically relative to the edges touch a ray drawn from the auxiliary point representing a mirror reflection of the point source relative to the boundaries of the partition with the selected equipotential, or measuring electrodes are placed on a line perpendicular to the boundary, symmetrically with respect to the supply source located close to the border, and the voltage on the measuring electrodes determine temporal variations of resistivity, characterized in that near the boundary line feature compensation point source, the current value which is set on the basis of ratioswhere I0, Ik- currents of the first and countervailing sources, ΔΨ1MNthe differential spatial function, which determines the position of the measuring electrodes relative to the first source, ΔΨ2MN- different is al spatial functions, determining the position of the measuring electrodes relative to the compensation source.



 

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