RU2568986C1 - Method of geological monitoring - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: claimed process exploits the application of magnetic probing of geological medium. Integral magnetic field developed in the result of net effects produced by the existing set of industrial electric power sources in the frequency range of 50 Hz to 1-2 kHz is used as the source. Evaluation of the electromagnetic field far and rear zone effects is made for zoning of territories by the rock electric resistance complying with informative zone. Then, magnetic field intensity components are recorded at every observation pint in three perpendicular directions at several magnitudes of azimuth for radial location components of the measuring unit. Spectral analysis of measured magnetic field is performed to define amplitude-frequency responses of each every component and to evaluate the latter in terms of apparent resistance. The latter are interpreted to get the info on spatial variation of electric resistance and anisotropic properties on rock in the range of effective depth of magnetic field propagation.

EFFECT: higher accuracy and data content.

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Description

The invention relates to the field of geophysics, and in particular to a method for geoelectrical exploration based on the use of industrial magnetic fields (PMF).

The PMP method can be used to solve geological, hydrogeological and environmental problems associated with the selection and mapping of objects with high electrical conductivity in urban areas. Most relevant is its use in order to forecast possible negative techno-geological processes during mine development of deposits.

A number of electrical exploration methods are known for detecting geological heterogeneities of the environment, based on the use of galvanic and inductive methods of excitation and registration of electromagnetic fields. These include various types of electrical and electromagnetic profiling and sensing (VES, EP, 43, ZSB, MTZ, etc.). However, in industrialized regions, their use becomes ineffective. This is due to the presence of various kinds of industrial structures and man-made interference, which significantly complicates the measurement process and reduces the information content of the results.

One of the ways to increase the efficiency of the application of electrical exploration methods in these conditions is to use electromagnetic fields generated by industrial electric power sources as a source. To date, several methods are known for using industrial electromagnetic fields in solving geological prospecting problems [2, 6-10].

One of the close to the present invention is a method of searching for good conductors in the magnetic field of industrial currents with a frequency of 50 Hz [2] by registering three orthogonal field components according to a system of parallel profiles with measuring the angle of inclination of the tension vector to the horizontal plane. The selection of informative components and interpretation are carried out on the basis of a comparative analysis with the known features of the geological structure of the previously studied territory. Another variation of this method is the invention (patent RU No. 2107932 C1, IPC G01V 3/08, published March 27, 1998), which considers the possibility of determining the position of linear conductive zones in the bowels of the earth by measuring the azimuths and inclination angles of the minor and major axes of the magnetic polarization ellipsoid field at the frequency of industrial current (patent RU No. 2107932 C1, IPC G01V 3/08, published 03/27/1998). As in the first case, measurements are carried out over a network of parallel profiles. At each point, according to the results of azimuthal observations, the direction to the lower space of the radius vector perpendicular to the plane built on the measured vectors is determined and the presence of conducting linear objects associated with the possible the presence of faults or sulfide ores.

The disadvantages of these methods include: 1) the need to perform surveys using a system of parallel profiles, which is not always possible due to the inaccessibility of individual sections of the study area, for example, with possible water cut, marshy, built-up areas, etc .; 2) informational limitations associated with the possibility of distinguishing only linearly elongated conductive objects, the uncertainty of the nature of changes in their depth, ignoring the possible effects of other industrial sources of electromagnetic fields.

The closest in technical essence and the achieved result to the proposed invention relates to the method described in the work of V.S. Titlinov [10], in which for the first time, in addition to the fundamental frequency (50 Hz), its individual harmonics were used. It was proposed to carry out field observations using standard equipment of impedance frequency soundings AChZ-78 with a nominal frequency range of 30-2500 Hz, into the measuring unit of which an additional set of frequencies of an industrial field of 50, 150, 250, 500, 1000 Hz was added. This equipment has a frequency bandwidth of 0.3 Hz and a noise floor of about 0.1 μV (at f = 50 Hz) and 0.02 μV at f = 1000 Hz). The main transmission line with a capacity of 110 kV was used as a source of industrial field. The method is implemented using the theory of infinite long cable. Registration was carried out using three industrial frequencies - 50, 150 and 250 Hz in combination with frequency sensing. A comparison of the obtained results with the data of frequency sounding made it possible to identify a number of important features of the used power transmission line field: a) the magnetic field is noticeably more stable than the electric field; b) when moving away from the power line by a distance exceeding half the wavelength, the apparent resistance curve calculated according to the power line field data is practically independent of the location system (vertical or horizontal) of the power line wires and is in good agreement with the frequency sounding curve; c) the observed field exceeds the threshold level of sensitivity of the device at a distance from the source (power 110 kV) up to 2.5 km.

The disadvantages of the prototype method are:

1) the field of a separate power line is used without taking into account the possible influence of a combination of different types of industrial field sources in highly urbanized areas, which reduces the accuracy and reliability of measurements; 2) there are no methods for quantifying the information content of the application of the method in specific geoelectric and electric power conditions with an arbitrary system of location of observation points; 3) when using AChZ-78 equipment, setting the frequencies of the industrial field is carried out subjectively, without taking into account and preliminary assessment of their information content.

The task of creating the present invention is to eliminate the disadvantages of the prototype, improving the accuracy, information content and manufacturability of the method of magnetic sensing, based on the use of industrial fields in solving geological, hydrogeological and environmental problems.

The problem is solved using the features specified in the claims common to the prototype, such as a method of geoelectrical exploration, based on the use of magnetic sensing of the geological environment, and distinctive essential features, such as using an integrated magnetic field as a result of the total exposure to the existing a set of industrial electric power sources in the frequency range from 50 Hz to 1-2 kHz, and based on an assessment of the influence of the far and near zones of the electromagnet of the total field, the territory is zoned according to the electrical resistance of the rocks corresponding to the informative zone, then the magnetic field components are recorded at each observation point in three orthogonal directions for several values of the azimuth of the location of the radial components of the sensor of the measuring setup, then the spectral analysis of the measured magnetic field is carried out, determine the amplitude-frequency characteristics of each of its components and recalculate the amplitude-frequency different characteristics in terms of apparent resistance, from the interpretation of which they obtain information about the spatial change in electrical resistance and anisotropic properties of the medium in the range of effective depths of magnetic field propagation.

The above set of essential features allows you to get the following technical result - improving the accuracy, information content and adaptability of the method of magnetic sensing based on the use of industrial fields.

The causal relationship of the distinguishing features of the invention with the achieved technical result is disclosed below.

The invention relates to ground-based methods of electrical exploration, based on the use of the phenomenon of electromagnetic induction, and can be used to study the physical state of the geological environment, with the allocation of any electron and ion-conducting objects (ore formations, water-saturated rocks, salt solutions) in solving search, engineering-geological and environmental tasks in urbanized areas.

The essence of the invention lies in creating a method for studying the structure and physical state of the geological environment, based on the use of the magnetic component of an alternating electromagnetic field, formed as a result of the total exposure to a wide range of sufficiently powerful power supply facilities - power lines, transformer substations, power regulators, induction furnaces, rectifiers, etc. taking into account the identified characteristic features of it, in particular, a) the multiplicity of harmonics of the integral field of the main Oh frequency (50 Hz); b) common-mode fields of various sources, due to the existing synchronization of the electric network within the industrial region; c) increased stability of the behavior of the field over time, due to both the stationary location of the sources and the weak dependence of the integral field on changes in the operation mode of individual sources of average power; d) the predominance of the vertical component of the magnetic field over its radial component due to the correspondence of the field of most industrial sources to the field of a vertical magnetic dipole. The method has the ability to predictively evaluate the effectiveness of its use in specific geoelectric and electric power conditions.

When using existing instrumentation that allows recording harmonics of the fundamental frequency (50 Hz) up to 10-12 orders of magnitude, the maximum penetration depth of such fields in the study of sedimentary rocks can reach several hundred meters, and the minimum depth starts from the first tens of meters (40- 50 m). The physical essence of this is explained on the basis of the basics of electrodynamics.

и противоположно направленного индуцированного вторичного поля $${\overline{H}}_{инд}\left(f\right)$$

According to the principle of electromagnetic induction, the magnetic field observed on the earth's surface can be represented as the sum of two main fields: primary $${\overline{H}}_0\left(f\right)$$

and oppositely directed induced secondary field $${\overline{H}}_{\mathrm{and}nd}\left(f\right)$$

при данной частоте поля f, соответствующей эффективной глубине зондирования [1, 5]Obviously, the larger the magnitude of the induced magnetic field, the greater the magnitude of the decrease in the amplitude of the observed field $$\left(\overline{H}\left(f\right)\right)$$

at a given frequency of the field f, corresponding to the effective sounding depth [1, 5]

^, являются:The main factors affecting the magnitude of the induced magnetic field $${\overline{H}}_{\mathrm{and}nd}\left(f\right)$$

^{They are:}

1) the presence of an electrically conductive body;

2) the rate of change of the primary field in a conducting medium.

.The higher the conductivity of the body, or the rate of change of the field, the more contrast is the manifestation of the conductive object, which can serve as any electron and ion-conducting bodies: ore formations, water-saturated rocks, salt solutions. The higher their conductivity, the greater the magnitude of the induction magnetic field excited by them and, accordingly, the greater the decrease in the observed field $$\overline{H}$$

.

The magnitude of the rate of change of the primary field in a conducting medium is determined by the ratio of the distance from the observation point r to the source with a wavelength λ, which is associated with the concept of near and far zones [1]. At small distances of the observation point from the source compared with the wavelength (r <λ / 2π), the field corresponds to the near zone, and for r> λ / 2π to the far zone. With the close proximity of the observation point to the source (r << λ), the magnetic field becomes almost uninformative - its dependence on the frequency and electrical resistance of the medium is lost [1]. The greatest manifestations of induction occur in the far zone.

Given the expression for the wavelength

in real conditions, if there are many sources within the region with different distances from the observation point, numbering hundreds and sometimes thousands of units, with their known location, the region of distribution of the far zone can be predicted. For this, the proposed parameter K _dz (f) can be used, which characterizes the degree of manifestation of the informative (far) zone in the observed integrated electromagnetic field, due to the set of N main industrial sources:

where r _i is the distance from the observation point to the i-th field source; f is the main (minimum) frequency (f = 50/60 Hz), which determines the condition for the implementation of the far zone for the entire frequency range f _{i of the} industrial field; ρ _en is the longitudinal resistance value corresponding to the upper boundary of the range of abnormally lowered resistances characteristic of the desired object.

On the basis of formula (6), zoning of the territory under investigation can be performed according to the values of ρ _en corresponding to the condition of the far zone. To calculate ρ _en using the formula obtained from (6):

Within the working area that meets the condition K _dz (f) >> 1, for example, K _dz (f) = 10, it is possible to obtain information about the geological section in a certain depth interval based on the principle of frequency sounding.

The proposed method in some cases can be used in the study of the geological environment and in the absence of information about each of the sources that contribute to the resulting field. This is based on the use of information on the above features of industrial fields. One of the criteria for informativeness is the assessment of the presence and degree of manifestation of the amplitudes of the magnetic field components for each of the used set of industrial frequencies (in the range from about 50 to 1000 Hz). The presence of industrial field frequencies and a sufficiently high level of the amplitudes of the magnetic field components that exceed the background level can serve as an indirect sign of the presence of a far zone.

When using the proposed method, it is possible to register the components of the magnetic field strength at each observation point in three orthogonal directions with several values of the azimuth of the location of the radial components of the sensor of the measuring installation.

Example 1

The technology for sensing the geological environment of the proposed method includes the following set of operations:

1) registration of the components of the magnetic field strength H _Xi (t), H _yi (t), H _z (t) at each observation point in three orthogonal directions in a given time interval (of the order of 20-40 s) at several values of the azimuth of the measurement setup;

2) spectral analysis of the measured field in order to determine the amplitude-frequency characteristics of each of the components of the observed magnetic field;

;3) recalculation of the amplitude-frequency characteristics into values of apparent resistance $${\rho }_k\left(\sqrt{\mathrm{one}/f}\right)={\rho }_k\left(\sqrt{T}\right)$$

;

- получение информации о пространственном изменении электрических свойств среды в интервале эффективных глубин распространения магнитного поля.4) interpretation of sounding graphs $${\rho }_k\left(\sqrt{T}\right)$$

- obtaining information about the spatial change in the electrical properties of the medium in the range of effective propagation depths of the magnetic field.

The implementation of this technology was performed using a hardware complex, including: registration sensors (type ERA-MA), analog-to-digital converter (type L-Card E440), GPS-navigator, mobile laptop, power supply and digital control system, using specially designed programs for recording and spectral analysis of the observed field [4], as well as the interpretation system of the PROBE programs (certificate No. 2005610058).

Unlike the prototype:

1) the field is not used as a separate power transmission line, but as an integral field, due to a combination of different sources, taking into account the general physical concepts and the results of experimental work;

2) a method has been developed for quantitatively evaluating the information content of using an industrial magnetic field in specific geoelectric and electric power conditions on the basis of calculating the integral characteristics of the far (informative) zone, as well as a method of regionalizing the territory according to the electrical resistance of rocks corresponding to the information zone;

3) the choice of operating frequencies is performed with their preliminary assessment in the process of spectral analysis of the observed field;

4) the possibility of recording the components of the magnetic field strength at each observation point in three orthogonal directions at several values of the azimuth of the location of the radial components of the sensor of the measuring setup, providing the opportunity to study the anisotropic properties of the medium.

The advantages of the proposed method include: 1) the use of a wide range of frequencies, including, in addition to the fundamental frequency (50 Hz), a set of harmonics up to 10-12 orders of magnitude generated by various kinds of electric power loads, allowing information on the physical properties of rocks occurring at different depths ( from the first tens to the first hundreds of meters); 2) the fundamental possibility of obtaining information about the physical state of the rock strata in the conditions of industrially developed regions, providing advantages relative to traditional methods of electrometry, subject to the influence of various kinds of industrial structures and man-made interference, significantly complicating the measurement process and the information content of the results obtained; 3) the ability to assess the information content of the application of the method in specific geoelectric and electric power conditions with an arbitrary system, the location of observation points that do not require profile observations on sub-parallel profiles; 4) the independence of the results of the interpretation of the observed data from the shape of the desired conductive body; 5) the simplicity of the technical design and the methodology of the work, ensuring the efficiency of forecasting possible negative events in highly developed industrial regions with the possibility of shooting at any time of the year in difficult industrial conditions.

Example 2

The following examples relate to the task of examining a water-proof stratum to ensure the safety of mining operations in the region of the Verkhnekamsk potash deposit, located in one of the industrially developed regions of the Perm Territory. In this case, the areas of salt karst formation serve as a conducting object. In conditions of natural occurrence, the electrical resistivity of salts is quite large and ranges from several thousand to the first tens of thousands of ohm-meters. Any violation of the salt mass opens access to underground water. The value of electrical resistivity, closely related to the mineralization of aqueous solutions formed as a result of leaching of salt rocks, can decrease to the first units, and in some cases, to fractions of units of an ohm meter. This degree of lowering the resistance values (hundreds, thousands of times) provides a sufficiently high contrast of the manifestations in the electromagnetic field of salt karst formation.

In FIG. Figure 1 shows a fragment of the survey results in the area capturing the region of the pillar and the flooded part of the worked out part of the carnallite stratum, which is in the depth interval 240-250 m. By contrast, the change in electrical resistance, changing by 8-10 times, the transition zone between worked and unworked is quite confidently recorded parts of the cut. These experimental observations of a well-known underground object, like physical modeling, confirm the penetration depth of an alternating magnetic field.

In FIG. Figure 3 shows an example of evaluating the information content of the proposed method in specific geoelectric and electric power conditions, a predictive assessment of the range of values of longitudinal electrical resistance of the medium, made by the totality of the main electrical sources in the area of the study area (from 200 kW to 700 MW) when the conditions of the far zone are fulfilled (K _dz ( f) = 10), as well as the nature of the distribution of the integral magnetic field.

A forecast estimate of the range of electrical resistance corresponding to the condition of the far zone shows that its value is in the range significantly exceeding the value of the anomalous resistance for a given territory ρ _an = 10 Ohm · m. This indicates the possibility of obtaining information about the zone of abnormally low resistances and the thickness of the enclosing rocks with a sufficient magnetic field for measurements. From the description and practical application of the present invention, other particular forms of its implementation will be apparent to those skilled in the art. This description and examples, drawings are considered as material illustrating the invention, the essence of which and the scope of patent claims are defined in the following claims, a combination of essential features and their equivalents.

LITERATURE

1. Vanyan L.L. Fundamentals of electromagnetic sounding. M .: Nedra, 1965.109 s.

2. Carvelis G.A. On the possibility of searching for good conductors in the magnetic field of stray currents with a frequency of 50 Hz. On Sat Methods of exploratory geophysics. Issues of electrical exploration of ore deposits. L .: NPO Geophysics, 1977, pp. 90-95.

3. Kolesnikov V.P., Diaghilev R.A. A system for registering industrial electromagnetic fields for electrical prospecting, Rec H3D. Certificate of state registration of computer programs No. 20144611489 of 04/04/2014

5. Landau L.D., Lifshitz EM. Electrodynamics of continuous media. - 4th ed., Moscow: FIZMATLIT, 2005 .-- 656 p.

6. Bobrovnikov N.V. Observation results of the vertical component of the electric field of industrial frequency // Theory and practice of electromagnetic methods of geophysical research. Yekaterinburg, Science, Ural Branch of the Russian Academy of Sciences, 1992.

7. Veshev A.V., Yakovlev A.V. The use of electromagnetic fields with a frequency of 50 Hz for electrical exploration // Geophysical methods of prospecting and exploration: Sverdlovsk: SGI, 1, 1975. P. 83-90.

8. Zakharov V.X., Parfenov A.V., Timokhin M.B. Amplitude-phase measurements of the magnetic field of industrial currents for the purpose of geological research // Geophysical methods of prospecting and exploration of ore and non-ore deposits. Sverdlovsk, 1980.59.

9. Saraev A.K., Ivochkin V.G., Pertel M.I., Nikiforov A.B. Possibilities of electromagnetic profiling at an industrial frequency of 50 Hz when studying the Vuoksinsky apatitone massif // Bulletin of St. Petersburg State University. St. Petersburg, 1998, 7.P. 63-68.

10. Titlinov B.C. On the possibility of using harmonics fields of a 50-period current of industrial power lines in multi-frequency electrical exploration // Theory and practice of electromagnetic methods of geophysical research. Yekaterinburg: Science, Ural Branch of the Russian Academy of Sciences, 1992.S. 64-77. - prototype.

Claims (1)

The method of geoelectrical exploration, based on the use of magnetic sensing of the geological environment, characterized in that the source uses an integrated magnetic field generated as a result of the total exposure to an existing set of industrial electric power sources in the frequency range from 50 Hz to 1-2 kHz, and based on the assessment of the effect the far and near zones of the electromagnetic field carry out the zoning of the territory in terms of the electrical resistance of the rocks corresponding to the informative zone, then The magnetic field components are recorded at each observation point in three orthogonal directions for several values of the azimuth of the location of the radial components of the sensor of the measuring setup, then a spectral analysis of the measured magnetic field is carried out, the amplitude-frequency characteristics of each of its components are determined, and the amplitude-frequency characteristics are calculated in values of apparent resistance, according to the interpretation of which they obtain information about the spatial m change in electrical resistance and anisotropic properties of the medium in the range of effective depths of magnetic field propagation.

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