RU2280269C1 - Method for geo-electric prospecting and device for realization of said method - Google Patents

Abstract

FIELD: geo-electric prospecting technology using electromagnetic field with alternating frequency, possible use for various searching tasks and geological research.

SUBSTANCE: in accordance to proposed method, in one of surface points of subject portion of geological environment, by means of generator with frame, which frame is positioned vertically and horizontally in turns, electromagnetic field is emitted. In points of surface distant from each other and from generator, by means of receiver with frame, which frame is positioned in turns vertically and horizontally, field is received and signal amplitudes are measured. On basis of measured amplitudes, character of change of apparent resistance is determined along the profile and also on basis of frequency cuts, and appropriate profiling and probing curves are built. By means of analyzing aforementioned curves, qualitative data interpretation is performed. By means of automatic inversion of aforementioned curves, quantitative data interpretation is performed. Proposed device contains generator and receiver of electromagnetic field. Generator contains synchronizer, microcontroller, controlled frequency synthesizer, amplifier and emitting frame, all in serial connection with each other. Receiver contains receiving frame, amplifier, mixer, analog-digital converter, microcontroller and synchronizer, all in serial connection with each other. Device also includes a radio channel for synchronization of generator and receiver.

EFFECT: increased speed and trustworthiness of information gathering about changes of apparent resistance of subject portion of geological environment both in horizontal and vertical directions.

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Description

The group of inventions relates to the field of geoelectrical exploration using an electromagnetic field of varying frequency and is intended for use in various kinds of exploratory and engineering-geological studies.

Known technical solutions for the implementation of geoelectrical exploration are based mainly on the frequency transmission of the geological environment by profiling or sounding. The former are characterized by high productivity, but only horizontal horizontal heterogeneities of the section are distinguished, and without their reliable depth reference (DE 19915016 A1, G 01 V 3/12, 05/05/2000; DE 4000018 A1, G 01 V 3/12, 11/08/1990 )

The second ones allow us to study the change in the resistance of the studied layer with depth, however, they are low productive (SU 868681 A, G 01 V 3/12, 09/30/1981; SU 1611101 A1, G 01 V 3/12, 01/10/2000).

Current development trends are due to attempts to combine these technologies, which makes it possible to obtain acceptable performance, characteristic for profiling, and sufficient informational content inherent in sounding.

Thus, in studies on direct current, multi-electrode devices are increasingly being used (FR 2402217 A1, G 01 V 3/02, 03/23/1982). However, the performance remains low due to the need to create a large number of groundings, especially in rocky or frozen soils. The problem is partially solved with the transition to contactless work, in which the braid with capacitive electrodes can be towed along the profile. However, this is technically possible only with small braids, so the depth of such studies in most cases is 10-15 meters.

In recent years, georadiolocation using the highest frequencies has also been used to study the geological environment (RU 2105330 C1, G 01 V 3/12, 02.20.1998; RU 2158015 C2, G 01 V 3/12, 20.10.2000; RU 2248585 C2 G 01 S 13/89, 03/20/2005). GPR allows you to quickly and with high detail to distinguish the boundaries of media with different dielectric constants. However, the depth in this case is again substantially limited and usually does not exceed 5 m.

A particularly promising area is the development of high-frequency electromagnetic research technology using harmonic fields of varying frequency (US 5185578 A, G 01 V 3/12, 02/09/1993; RU 2213982 C1, G 01 V 3/12, 02/09/1993; RU 2112997 C1 , G 01 V 3/12, 06/10/1998; SU 1699273 A1, G 01 V 3/12, 07/30/1994).

Of the above technical solutions, the closest to the proposed method is the method of geoelectro-prospecting, which involves the study of the geological environment with the combined use of profiling and sensing and including, in particular, radiation and reception of an electromagnetic field with a varying frequency, as well as measuring the amplitudes of a signal characterizing the received electromagnetic field (SU 1699273 A1).

Of the above technical solutions, the closest to the proposed device is a device for geoelectrical exploration, which includes an electromagnetic field generator with a frequency modulator and synchronizer, an electromagnetic field receiver with a local oscillator, a mixer, an amplitude detector and a synchronizer, as well as a synchronization radio channel (SU) connected between the generator and receiver 1699273 A1).

The disadvantages of the indicated method and device are determined by a narrow distribution area, covering only cross-hole radio wave transmission, low reliability of the information received, due, in particular, to the antenna effect of the logging cable used, and not high performance.

The task of the group of inventions is to expand the field of practical use of such combined method and device and increase their accuracy and efficiency. The technical result consists in providing the ability to quickly and with increased reliability of obtaining information about changes in the apparent resistance of the studied section of the geological environment both in horizontal (during profiling) and in vertical (when sensing) directions.

The problem is solved by the proposed method, according to which at one point on the surface of the studied area of the geological environment, an electromagnetic field is emitted by a generator with a frame arranged vertically and horizontally alternately, the radiation frequency is periodically changed from minimum to maximum values, at points that are apart from each other and from the generator the surface of the receiver with the frame, placed alternately vertically and horizontally, take an electromagnetic field, measure the signal amplitude, character imitating the accepted electromagnetic field, for the entire spectrum of frequencies used, the measured amplitudes reveal the nature of the apparent resistance change along the profile and the depth of the frequency sections and construct the corresponding profiling and sounding curves, by analyzing the obtained curves, qualitatively interpret the data with the definition of bodies and layers that have extreme value of apparent resistance, and by automatic inversion of the obtained curves, a quantitative interpretation of the data the transition to the bulk of the geoelectric model of the structure of the investigated area of the geological environment.

When the electromagnetic field is emitted horizontally and vertically by a frame, the radiation frequency is periodically changed from 100 Hz to 1 MHz according to a linear law.

At surface points spaced apart from each other and from the generator, the electromagnetic field is received alternately by the same receiver or simultaneously by several identical receivers.

When receiving an electromagnetic field, measure the amplitude of the EMF arising in the receiving frame.

To solve this problem, it is also proposed a device containing an electromagnetic field generator, which includes a serially connected synchronizer, a microcontroller, a controlled frequency synthesizer, an amplifier and a radiating frame installed with the possibility of alternating vertical and horizontal arrangement, a keyboard and a display connected to the input / output a microcontroller, a battery voltage converter connected to the power input of the amplifier, an electromagnetic field receiver, It also includes a receiving frame connected in series with the possibility of alternating vertical and horizontal arrangement, an amplifier, a mixer, an analog-to-digital converter, a microcontroller and a synchronizer, a local oscillator connected to one of the mixer inputs, a keyboard and a display connected to the input / output of the microcontroller, and also a synchronization radio channel, including a transmitting unit with a transmitting antenna, connected to the output of the receiver synchronizer, and a receiving unit with a receiving antenna, connected ny generator to the input synchronizer.

In the electromagnetic field generator, the frequency synthesizer has a frequency spectrum from 100 Hz to 1 MHz, and the microcontroller is configured to change the frequency of the synthesizer according to a linear law.

In the receiver of the electromagnetic field, the microcontroller is configured to estimate the amplitude of the EMF arising in the receiving frame.

The device may have several identical electromagnetic field receivers.

Figure 1 presents the General structure of the radiation and reception of the electromagnetic field, characteristic for this group of inventions. Figure 2 shows the functional diagram of the proposed device for geoelectrical exploration, which implements the proposed method. Figure 3 shows the multi-frequency signal used for emitting an electromagnetic field.

The set of equipment includes a digital portable generator 1 of the electromagnetic field and one or more digital portable receivers (meters) 2 of the electromagnetic field (figure 1).

The composition of the electromagnetic field generator 1 includes a synchronizer 3 (Fig. 2), a microcontroller 4, a controlled frequency synthesizer 5, an amplifier 6, an emitting frame (loop) 7, a keyboard and a display (text), conventionally combined in block 8, a voltage converter 9 and battery 10. Synchronizer 3, microcontroller 4, controlled synthesizer 5 frequencies, amplifier 6 and emitting frame 7 are connected in series. The keyboard and display unit 8 is connected to the input / output of the microcontroller 4. The Converter 9 voltage of the battery 10 is connected to the power input of the amplifier 6. The emitting frame 7 is installed with the possibility of alternating vertical and horizontal locations.

The composition of the receiver (meter) 2 of the electromagnetic field includes a receiving frame (loop) 11, an amplifier 12, a mixer 13, an analog-to-digital converter 14, a microcontroller 15, a synchronizer 16, a local oscillator 17, a keyboard and a display (graphic), conventionally combined in block 18 The receiving frame 11, amplifier 12, mixer 13, analog-to-digital converter 14, microcontroller 15 and synchronizer 16 are connected in series. The local oscillator 17 is connected to one of the inputs of the mixer 13. The keyboard and display unit 18 are connected to the input / output of the microcontroller 15. The receiving frame 11 is installed with the possibility of alternating vertical and horizontal location.

The synchronization radio channel includes a transmitting unit 19 with a transmitting antenna and a receiving unit 20 with a receiving antenna. The transmitting unit 19 is connected to the output of the synchronizer 16 of the receiver 2. The receiving unit 20 is connected to the input of the synchronizer 3 of the generator 1.

The technology of high-frequency electromagnetic research in this group of inventions is based on the use of an artificial electromagnetic field in the frequency range from 100 Hz to 1,000,000 Hz (1 MHz). The field with the intensities H ₁ , H ₂ , H ₃ (Fig. 1) is excited by the generator 1. In this case, the initial task of the necessary frequency spectrum f ₁ , f ₂ , f ₃ (Fig. 3) is carried out by the microcontroller 4 (Fig. 2) and a synthesizer frequency 5 with the corresponding keyboard action and displaying the task on the display in block 8. The amplification of the frequency signals is performed by an amplifier 6, the required supply voltage for which is generated using a converter 9 connected to the output of the battery 10. A frequency-varying electromagnetic field is emitted by frame 7, position Aga alternately vertically (for profiling) and horizontally (for sensing). Periodic switching of frequencies in a given spectrum from minimum to maximum values is carried out automatically.

The measurements are carried out by the receiver 2. The electromagnetic field is perceived by the frame 11, amplified by the amplifier 12 and, together with the signal from the local oscillator 17, is sent to the mixer 13. Then, in the analog-to-digital converter 14, the analog signal from the output of the mixer 13 is converted into a digital signal, which is sent for evaluation to microcontroller 15. The evaluation results are displayed on the display in block 18. Copying data from the receiver 2 to an external standard computer is carried out via infrared.

The main parameters of the generator 1 and receiver 2, in particular the frames 7 and 11, are selected in such a way as to ensure reliable recording at distances up to 100 m from the generator 1.

The maximum research depth does not exceed the distance from the generator 1 to the receiver 2. The change in the electrical properties of the rocks from the surface to this depth can be traced due to periodic changes in the frequency of the electromagnetic field, for example, according to the linear law (only three frequencies are conventionally shown in Fig. 3 - f ₁ , f ₂ and f ₃ ). The amplitude arising in the frame 11 of the EMF E increases if the field passes through the conductive rock. In this case, the upper part of the section (to a depth of about a meter in conductive and several meters in high-resistance media) is a “blind zone”. The sounding interpretation is applicable at distances from the generator 1 to the receiver 2 constituting 20-100 m. If it is less than 20 m, then only shallow highly conductive objects can be localized.

For research, usually two people are needed. The operator works with the receiver 2 and the receiving frame 11 included in it and sequentially moves from one point on the surface of the investigated area to another. The assistant deals with the generator 1 and the emitting frame 7 included in it. Simultaneous registration of the electromagnetic field by several receivers 2 is also possible with the participation of several operators.

With automatic frequency switching, the recording time at each point is several seconds. Productivity can reach hundreds of points per day and depends mainly on the terrain. The received data is transferred to a standard computer for interpretation using special software.

The synchronization of the generator 1 and receiver 2 is performed using high-frequency crystal oscillators. In this case, a radio synchronization channel is used. In case of possible malfunctions of the proposed device, i.e. when the generator 1 and the receiver 2 are out of sync, the microcontroller 15 is subjected to the keyboard of the block 18 to adjust the clock frequency of the receiver 2. The synchronization signal is transmitted to the generator 1 using the synchronizer 16, the transmitting block 19, the receiving block 20 and the synchronizer 3.

In the process of studying the geological environment, the measured amplitudes arising in frame 11 of the EMF reveal the nature of the change in apparent resistance (impedance) along the profile and in the depth of the frequency sections and construct the corresponding profiling and sounding curves.

A qualitative interpretation of the data (can be carried out in the field) comes down to an analysis of the obtained curves. In this case, bodies and layers with an extreme value of apparent resistance are determined.

A quantitative interpretation of the data implies an automatic inversion of the obtained curves with a transition to a volumetric geoelectric model of the structure of the studied section of the geological environment. It is possible to take into account a priori information and link with the results obtained at neighboring points.

It should be noted that the structure of the electromagnetic field changes significantly with increasing frequency. At low frequencies (≪1 MHz) conduction currents prevail, and the field mainly depends on the electrical resistance of the medium (ρ). At high frequencies (≫1 MHz), bias currents are more intense, and the dielectric constant of the medium (ε) makes the main contribution.

At frequencies of the order of 1 MHz, the intensities of conduction currents and bias currents are comparable. It can be estimated by considering the ratio of the values of the densities of conduction currents (j _PR ) and bias (j _SM ): j _PR / j _SM = 1 / (ω · ρ · ε), where ω = 2π · f is the circular frequency. Table 1 shows the values corresponding to media with different electrical properties and different frequencies.

Table 1 f Hz The ratio of the densities of conduction currents and bias at ε = 5 and ε = 25 ρ = 10 Ohm · m ρ = 30 Ohm · m ρ = 100 Ohm · m ρ = 300 Ohm · m ρ = 1000 Ohm · m ε = 5 ε = 25 ε = 5 ε = 25 ε = 5 ε = 25 ε = 5 ε = 25 ε = 5 ε = 25 640000 562.5 112.5 187.5 37.5 56.25 11.25 18.75 3.75 5.625 1.125 320,000 1125 225 375 75 112.5 22.5 37.5 7.5 11.25 2.25 160,000 2250 450 750 150 225 45 75 fifteen 22.5 4.5 80,000 4500 900 1500 300 450 90 150 thirty 45 9 40,000 9000 1800 3000 600 900 180 300 60 90 eighteen 20000 18000 3600 6000 1200 1800 360 600 120 180 36 10,000 36000 7200 12000 2400 3600 720 1200 240 360 72 5000 72000 14400 24000 4800 7200 1440 2400 480 720 144 2500 144,000 28800 48000 9600 14400 2880 4800 960 1440 288 1250 288000 57600 96000 19200 28800 5760 9600 1920 2880 576 625 576000 115200 192000 38400 57600 11520 19200 3840 5760 1152 312.5 1152000 230400 384000 76800 115200 23040 38400 7680 11520 2304 156.25 2304000 460800 768000 153600 230400 46080 76800 15360 23040 4608

From table 1 it is seen that conduction currents prevail in almost the entire considered frequency range and for all types of media. However, at high frequencies in poorly conducting media, the density of bias currents approaches the density of conductivity currents (values corresponding to the contribution of bias currents of more than 1% are shown in bold). Thus, in a qualitative analysis of data in the frequency range under consideration, bias currents can be neglected, but in the numerical solution of direct and inverse problems, they must be taken into account. In this case, it becomes possible to determine the ε values of rocks, but the complexity increases, and the stability of solving the inverse problem decreases.

, где

- модуль волнового числа среды (μ - магнитная проницаемость).The depth of research is determined by two factors: the distance from the source to the receiver r and the frequency f. With their close proximity, the primary field of the source significantly exceeds the field of secondary currents induced in the medium and carrying information about its properties. The corresponding region is called the near zone of the source. Quantitatively, getting into the near zone is estimated from the inequality

where

- the modulus of the wave number of the medium (μ - magnetic permeability).

. Значения h_δ приведены в таблице 2.The dependence of the research depth on the frequency is due to the skin effect. It consists in the fact that the field damps with depth the faster, the higher the oscillation frequency of the field f and the lower the resistance of the medium ρ. The depth at which the field weakens significantly (e ≈ 2.7 times) is called the skin thickness h _δ . It characterizes the depth of research at a given frequency and is equal to

. The values of h _δ are shown in table 2.

table 2 f Hz Skin thickness h _δ , m ρ = 10 Ohm · m ρ = 30 Ohm · mm ρ = 100 Ohm · m ρ = 300 Ohm · m ρ = 1000 Ohm · m 640000 2.0 3.4 6.3 10.9 19.9 320,000 2.8 4.9 8.9 15.4 28.1 160,000 4.0 6.9 12.6 21.8 39.8 80,000 5.6 9.7 17.8 30.8 56.3 40,000 8.0 13.8 25.2 43.6 79.6 20000 11.3 19.5 35.6 61.6 10,000 15.9 27.6 50.3 87.2 5000 22.5 39.0 71.2 2500 31.8 55.1 1250 45.0 78.0 625 63.7 312.5 90.0 156.25

, при r=100 м (расстояние между генератором 1 и приемником 2 100 м), значения h_δ не приведены, поскольку при этом происходит переход в неинформативную ближнюю зону. Для случаев, когда

, при r=20 м значения выделены жирным шрифтом. Таким образом, в однородной среде глубинность исследований сопоставима с размером установки (в реальных неоднородных средах она может несколько отличаться).For cases in which

, at r = 100 m (the distance between the generator 1 and the receiver 2 100 m), the values of h _{δ are} not given, since this leads to a transition to the uninformative near zone. For cases when

, at r = 20 m the values are shown in bold. Thus, in a homogeneous medium, the depth of research is comparable with the size of the installation (in real inhomogeneous media it may vary slightly).

In the practical implementation of the proposed group of inventions, the number shown in tables 1 and 2 of the operating frequencies and the duration of work at each frequency are set by the user.

Data interpretation software features predetermine:

- reading data from files copied from the meter;

- visualization of sounding curves, profiling graphs, frequency sections and apparent resistance maps;

- calculation of sounding curves for the vertical and horizontal components of the fields of vertical and horizontal magnetic dipoles, taking into account the resistivity, dielectric and magnetic permeabilities of the layers;

- solving the inverse problem (calculation over the field — the object) with the possibilities of regularizing the solution through the use of a priori information and linking the results obtained at neighboring points;

- construction of geoelectric sections and maps of electrical properties.

Thus, this group of inventions allows you to quickly and with increased reliability to obtain information about the change in the apparent resistance of the studied section of the geological environment. This provides:

- direct searches and localization of ore bodies with a high concentration of metals;

- Searches and exploration of deposits of ores with low concentrations of metals (including noble) and non-metallic ores (including uranium);

- Searches and exploration of coal deposits and oil shale;

- Searches and localization of kimberlite pipes;

- identification of groundwater (fresh, mineral, thermal), mapping and determination of the depth of aquifers;

- survey for the construction of industrial, agricultural, residential and transport facilities - assessment of soil properties and the structure of the geological environment;

- study of the technical condition of mine workings (including water cut) using both ground and underground (mine) surveys;

- mapping of permafrost, determining the depth of their roof and sole, identifying local taliks;

- study of zones of increased geodynamic hazard - identification of karst-suffusion zones and tectonic disturbances, the study of landslides;

- mapping of soil pollution with oil products and other substances;

- study of the geological structure of the bottom of freshwater areas;

- search and study of the status of large underground technogenic and archaeological sites.

Claims (9)

1. The method of geoelectrical exploration, according to which at one point on the surface of the studied area of the geological environment, an electromagnetic field is emitted by a generator with a frame arranged vertically and horizontally alternately, the radiation frequency is periodically changed from minimum to maximum values, at surface points spaced from each other and from the generator the receiver with the frame, placed alternately vertically and horizontally, take an electromagnetic field, measure the amplitude of the signal characterizing the received ele a magnetic field, for the entire spectrum of frequencies used, from the measured amplitudes reveal the nature of the apparent resistance change along the profile and the depth of the frequency sections and construct the corresponding profiling and sounding curves, by analyzing the obtained curves, make a qualitative interpretation of the data with the determination of bodies and layers having an extreme value of the apparent resistance, and by automatically inverting the obtained curves, a quantitative interpretation of the data is carried out with the transition to volumetric geoelectric model of the structure of the studied area of the geological environment. 2. The method according to claim 1, according to which when the electromagnetic field is emitted by a horizontally arranged frame, the radiation frequency is periodically changed from 100 Hz to 1 MHz according to a linear law. 3. The method according to claim 1, according to which in the surface points spaced from each other and from the generator, the electromagnetic field is received alternately by the same receiver. 4. The method according to claim 1, according to which, in the surface points spaced from each other and from the generator, the electromagnetic field is received simultaneously by several identical receivers. 5. The method according to any one of claims 1 to 4, according to which, when receiving an electromagnetic field, the EMF amplitudes arising in the receiving frame are measured. 6. A device for geoelectrical exploration, containing an electromagnetic field generator, which includes a serially connected synchronizer, a microcontroller, a controlled frequency synthesizer, an amplifier and an emitting frame installed with the possibility of alternating vertical and horizontal arrangement, a keyboard and a display connected to the input / output of the microcontroller, a battery voltage converter connected to the power input of the amplifier, an electromagnetic field receiver, which includes the receiver frame, which is installed with the possibility of alternating vertical and horizontal arrangement, an amplifier, a mixer, an analog-to-digital converter, a microcontroller and a synchronizer, a local oscillator connected to one of the mixer inputs, a keyboard and a display connected to the input / output of the microcontroller, and also a radio channel synchronization, including a transmitting unit with a transmitting antenna, connected to the output of the receiver synchronizer, and a receiving unit with a receiving antenna, connected to a synchronization input generator torus. 7. The device according to claim 6, in the electromagnetic field generator of which the frequency synthesizer has a frequency spectrum from 100 Hz to 1 MHz, and the microcontroller is configured to change the frequency of the synthesizer according to a linear law. 8. The device according to claim 6, in the electromagnetic field receiver of which the microcontroller is configured to estimate the amplitude of the EMF arising in the receiving frame. 9. The device according to any one of claims 6 to 8, in which there are several identical electromagnetic field receivers.

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