WO2015088466A1

WO2015088466A1 - Geophysical exploration method

Info

Publication number: WO2015088466A1
Application number: PCT/UA2014/000093
Authority: WO
Inventors: Igor Borisovich BURKYNSKYY; Anatoliy Stepanovyc DOVHOPOLY; Igor Oleksandrovych ZGUROV; Igor Leonidovych UCHYTEL'; Tsezar Mykolayovych SULTAN; Victor Veniaminovych LUKIN; Oleksandr Mykolayovych POLOVENKO; Oleg Romanovych CHERTOV
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-06-26
Filing date: 2014-08-14
Publication date: 2015-06-18
Anticipated expiration: 2016-12-26

Abstract

The geophysical exploration method involves synchronous measurements of an intensity of the natural pulsed electromagnetic field of the Earth (NPEFE) in different parts of the area being explored with all measurements are taken in a range of very low frequencies in at least two different directions to receive a signal by routing and reference devices, and first the sensitivity and identity of reception of signals by all routing and reference devices are adjusted, the antennas for the same reception channels of all involved devices are oriented in same preset directions of space, the graphs with spatial changes in the intensity of fields along the work profile are construed, any geophysical anomaly is identified in the profile being explored, with measuring available structural and lithological heterogeneities by an anomalous change in the intensity of NPEFE, the boundaries of anomalies are mapped and the results are given a geological interpretation. The routing devices for measurement of the electromagnetic field for subsequent compensation of noises from local and remote sources are additionally installed, at least two routing devices are installed in each peg, the profiling is made with simultaneous measurement of signals by all routing and reference devices with the preset discreteness, the digital filtering is provide for selection of signals in the context of noise, the group processing is given to signals from routing and reference devices by setting admissible ranges for factors of cross-correlations between signals of the corresponding channels of different routing devices, different routing and reference devices, a time interval is set for calculations of factors of cross-correlations for signals, calculations of factors of cross-correlations between signals from the corresponding channels of routing devices and between signals of the corresponding channels of routing and reference devices, values of each calculated factor of cross-correlations for each routing devices are compared with corresponding admissible ranges of factors for cross-correlations of signals, with further determination of a signal from the routing device as a NPEFE signal in the point of current location of the routing device, if the values of the calculated cross- correlation factors correspond to the preset corresponding admissible range of cross-correlation factors, then a number of signals determined as NPEFE signals is calculated in each point of current locations of the corresponding routing device for each corresponding device within the time interval in accordance with the preset discreteness of signal measurements, and the intensity of NPEFE in those points is determined for the further mapping of the boundaries of geophysical anomalies, on the basis of the intensity value of NPEFE in different points of the area being explored.

Description

Geophysical exploration method

This invention relate to the geophysics, in particular to the field of electromagnetic prospecting which uses measurements of the natural pulsed electromagnetic field of the Earth (NPEFE) and can be used for detection and mapping of structural and lithological heterogeneities of the Earth's crust, prospecting and exploration of mineral deposits, including deposits of oil and gas when there is an disturbance from local sources (located in the exploration area and in its immediate vicinity) and remote sources.

Geophysical explorations which are focused on prospecting and exploration of mineral resources often have certain complications associated not only with a complexity of geological structure in the exploration area, but also with the technical capabilities of explorations. One of the problems which exists, when conducting a geophysical exploration, is the presence of electromagnetic disturbances, including unwanted physical phenomena or effects of electric, magnetic or electromagnetic fields, electric currents or voltages from external or internal sources that disturb the normal operation of technical equipment or cause or worsen technical properties and parameters.

In addition, electromagnetic disturbances may be of natural origin (cosmic noise, radio emission of the Earth and objects of the Solar system, atmospheric disturbances of the Earth) or they may also be generated artificially (industrial or production noises such as radiation of production machines, household appliances, etc. contact disturbances such as noise that occurs during transition processes and station noise from other radio electronic devices such as broadcasting stations, etc.).

Thus, the most of methods and devices for geophysical exploration are aimed at creating the system and the algorithm that would ensure getting the most accurate results, even in case of existence of electromagnetic disturbances. Many similar methods and related geophysical exploration devices are knows, among which the following one is the closest to the invention by essential features.

A device for recording the natural pulsed electromagnetic field of the Earth are known which may employ the method of geophysical survey, that includes a magnetic antenna connected to an amplifier connected in series with a block of filters, an amplifier with programmable gain ratio, an analog-digital converter, a computer microprocessor and a RAM device with independent power source and an amplitude discriminator with programmable discrimination threshold, which is connected with its input to the output of the amplifier with programmable gain ratio. Further, this device includes a multi-channel adaptive notch filter with parallel channels, which input is connected to the amplifier, and its first output is connected to the filter and second output - to the computer microprocessor, while the multi-channel notch filter has each channel connected to a common input and includes a narrow-band filter, an amplitude detector, a controlled threshold circuit and a disturbance indicator, which are connected in series, as well as a key circuit which signal input is connected to an output of the narrow-band filter, and its control input is connected to the second output of controlled threshold circuit, and its output is connected to the corresponding input of an adding circuit with common output and to the corresponding input of the computer microprocessor (Patent UA 70417 published on October 15, 2004, Bulletin No. 10).

One of the disadvantages of the method employed by that known device is that does not have any instruments for selecting NPEFE signals of local origin that convey the information about a geophysical structure of the area being explored from a total flow of NPEFE signals which may also include disturbances from local and remote sources. In turn, this would has allowed enhancing the accuracy of data on geophysical anomalies and the mapping based on those data and, therefore, the results from finding out any available locations of deposits of minerals, hydrocarbons in particular. By its nature, the method of geophysical exploration which was chosen as a prototype is the most likewise, as it involves synchronous measurements of an intensity of the natural pulsed electromagnetic field of the Earth (NPEFE) in different parts of the area being explored with all measurements are taken in a range of very low frequencies in at least two different directions to receive a signal, the construction of graphs with spatial changes in the intensity of fields along the work profile, which gives a geological interpretation of the results, and an area with low values of NPEFE intensity is referred to promising areas containing oil or gas, record additionally the time of arrival and the number of pulses from the natural pulsed electromagnetic field of the Earth, and, first, the antennas of n- devices which record the natural pulsed electromagnetic field of the Earth, where n = 2, 3, 4, are mounted at a maximum distance of 1 m from one another and the antennas for the same channels are oriented in same preset directions of space, the sensitivity of channels is adjusted for a typical 24 hour routine of NPEFE, then, by comparing the device readings with one another, the sensitivity is equalized for those channels which receive signals from the same directions, and the resulted device settings are stored by adjusting the attenuation and magnitude factors for reference voltages, then the synchronous measurements of fields time variations are taken by all devices during working hours, then the mean intensity values are determined for each device and each direction of signal reception, the graphs of mean intensity changes in time are construed, comparing the designed graphs with one another, the devices are sorted by reference devices and stopping accuracy devices, choosing those devices which readings are close to the mean reading values of all devices as stopping accuracy devices, a basic device is chosen among stopping accuracy devices, which has recorded the values of signal intensity the average that are the closest to the mean reading values of stopping accuracy devices, the transfer functions which display the difference in readings of each device and the readings of the basic device during a certain time of work are determined for all devices and each direction of signal reception, the graphs are construed for those dependencies and smoothed by a sliding window of such duration that they do not have sharp jumps, then the accuracy stopping devices, including the basic one, are installed in selected point of the area being explored, orienting the antennas of their same reception channels in the same preset directions of space, the measurement are taken by standard time signal in continuous mode by using the parameters determined in the settings, the profiling is made by preset discontinuous polling of channels, using routing instruments which antennas are oriented in space so that their orientation coincides with the orientation of the antennas of accuracy stopping devices and the setting and measurement parameters correspond to previously set values, the measured NPEFE parameters variations along the profile are determined, a conclusion is made as to a geophysical anomaly by taking out the time variations registered by accuracy stopping devices from the readings of routing devices in the explored profile, the boundaries of anomalies are mapped and the results are given a geological interpretation with measuring structural and lithological heterogeneities by changes of signal intensity, and the faults are detected by higher signal intensity values, considering that big and transcontinental faults increase the signal intensity in the area of edges and lower the signal intensity in the axial zone, and when mapping the boundaries of hydrocarbons or other minerals, and the readings of routing devices are compared with the readings of accuracy stopping devices installed in a productive area, and those areas where the parameters being recorded are slightly different from the parameters being registered by accuracy stopping devices are referred to, productive areas and the rest of areas is considered unproductive, the field boundary is outlined outside the boundaries of productive and unproductive areas, if any information about area productivity is available, when taking the above mentioned measurements, the areas with highest and lowest intensity of NPEFE are identified, then, using other methods of geophysical exploration and drilling, the presence of oil or gas is identified in one of the anomalous areas, and based on the consolidated results, the rest of the area is divided into productive and unproductive ones (WO2010/082868 Al published on July 22, 2010).

The disadvantage of the prototype method is that no additional digital filtering is performed to select the signals when any disturbances are present. The absence of that reduces the possibility to receive quality results as the use of digital filtering is suppressing narrowband disturbances. In addition, this method does not provide a group processing of signals from routing and reference stations, which allows for selection of NPEFE signals from impulse noise, allowing you to record NPEFE with much better quality when any disturbances are present.

The task of this invention, which is a method of geophysical exploration, is to raise effectiveness of the detection and mapping of structural and lithological heterogeneities of the crust on the basis of measurements of parameters of pulsed electromagnetic field of the Earth, including geological faults and places of their crossing, cracks, boundaries of dissimilar rocks and hydrocarbon traps, by improving the known prototype-backed method of geophysical exploration.

The known method of geophysical exploration based on the recording of the natural pulsed electromagnetic field of the Earth is improved by increasing the efficiency of selection of the NPEFE pulses of local origin, the parameters of which convey the information about the geophysical structure of an area being explored in the context of background disturbances from local (located in the area being explored and its immediate vicinity) and remote sources, including natural disturbances (atmospheric and lithospheric) origin.

The set task is reached so that the method of geophysical exploration, as well as in the prototype, includes synchronous measurements of the intensity of the natural pulsed electromagnetic field of the Earth (NPEFE) in different parts of the area being explored, and all the measurements are taken in the range of very low frequencies at least in two different directions of signals reception by reference and routing devices, first the sensitivity and identity of signal reception by reference and routing devices are adjusted, the antennas of the same reception channels in all the used devices are oriented in the same preset directions of space, the graphs of spatial intensity changes in electromagnetic fields are construed along the profile of works, any presence of geophysical anomalies are determined in the target profile and the presence of structural and lithological heterogeneities are measured by anomalous changes in the NPEFE, the boundaries of anomalies are mapped, and a geological interpretation is prepared for the resulted values in accordance with the claimed invention, the reference devices are additionally installed to measure the electromagnetic field to further compensate disturbances from local and remote sources, at least two routing devices are installed in each peg, the profiling is made with simultaneous measurements of signals by all routing and reference devices with the preset discreteness, the digital filtering is provided for selection of signals in the context of disturbances, the signals from reference and routing devices are processed by setting admissible ranges of factors for cross- correlations of signals from different routing and reference devices, the time interval is set for calculation of factors for cross-correlations of signals and calculations for cross-correlation factors between corresponding channels of routing devices and between signals of corresponding channels of routing and reference devices, each calculated cross-correlation factors for each routing device are compared with corresponding admissible ranges of factors for cross- correlations of signals, with further determination of the signal from the routing device as a NPEFE signal in the point of current location of the routing device, if the values of the calculated cross-correlation factors correspond to the preset corresponding admissible range of cross-correlation factors, then the number of signals determined as NPEFE signals is calculated in each point of current locations of the corresponding routing device for each corresponding device within the time interval in accordance with the preset discreteness of signal measurements, and the intensity of NPEFE in those points is determined for the further mapping of the boundaries of geophysical anomalies, on the basis of the intensity value of NPEFE in different points of the area being explored. The following cause-effect relationship exists between the essential features of the invention and the results achieved with the application thereof.

In the process of the explorations with application of the known method, which is, in particular, known for its technical level, research on improving the efficiency of the detection and mapping of structural and lithological heterogeneities of the crust performed, based on measurements of the natural pulsed electromagnetic field of the Earth, and tested the proposed method. During those researches, it was found that a technical result is achieved only when some additional works are performed and the calculations are made in relation to the filtering and processing of the data obtained during the research.

To accomplish the set goal, such as the improvement the efficiency of the detection and mapping of structural and lithological heterogeneities of the crust on the basis of measurements of parameters of the pulsed electromagnetic field of the Earth, it was determined about the need to create a method that would improve the exploration data in the context of disturbances, by upgrading the operations and activities related to digital filtering and group processing of the information received.

In the course of the research, the signals were recorded by the same type devices with similar characteristics, which are conditionally divided into routing devices and reference devices. In the process of measurement, the reference devices are located permanently in points selected for recording, and the routing devices may be moved among selected pegs along the profile. The reference devices are used for recording the time variations of the magnetic component in the field.

The researches show that the additional installation of reference devices for further compensation of disturbances from local and remote sources will allow you first to additionally record the intensity disturbance signals from local sources of noise. To do this, the devices (reference and routing) record the intensity of the signal near the man-made sources of disturbance (eg, electric power generating plants, transformer substation, surface and underground power lines, production capacities, etc.), and the intensity of the disturbing signal in the area of pegs on the profile is recorded simultaneously. This will help, by conducting an analysis, to set the intensity of signals from local sources of disturbance in the area being explored.

The analysis of the intensity of signals from local sources of disturbance in the area being explored allows you to specify the places of installation of reference devices in the area only from local sources of disturbance, the signals of which were recorded in the area being explored, as well as to provide an option to install reference devices for recording signals from remote sources of noise at a distance of 10-30 km from the area of exploration.

To obtain the required results in the selection of weak signals of NPEFE, at least two routing devices record are installed at peg. The installation of at least two routing devices at a distance of 1 m will allow for a verification of the information received, since the signals at such small distances may not be materially different, that may be a proof that they belong to the given point of profile being explored and not be a noise of the device.

The profiling at simultaneous measurements of signals by all routing and reference devices with the preset discreteness is provided by taking the following steps for conducting the research related to information processing. In addition, the discreteness of signal measurements by all routing and reference devices, the permissible ranges of cross-correlation between signals from the corresponding channels of different devices, the value of the time interval for calculating the cross-correlation factor is determined by the inventor itself, based on the results of statistical processing of data records from different areas of exploration, calculations, manual selection of respective ranges and different thresholds. These parameters are subject to refinement for each new area of exploration. Thus, in the course of many studies, there have established the discreteness of signal measurement signals which starts from 1 sec or more. In addition, it was the statistics which exactly provided the ranges of cross- correlation factors for the area given in the following example. The data values of the ranges are as follows:

0.7...1 - range of similarity;

(- 0.3)...(+ 0.3) - range of differences.

Unlike the prototype, the proposed method provides for the additional digital filtering to select the signals in the terms of noise. The automatic digital filtering procedure is effected with using the wavelet analysis of output channel known from the art (eg, Daniel TL Lee, Akio Yamamoto, Wavelet Analysis: Theory and Applications, Hewlett-Packard Journal, December 1994). Due to the use of the digital filtering, the narrowband noise manifested as peaks in the spectrum of the signal is suppressed, provided that these peaks are simultaneously present in the signals from reference and routing devices.

After the digital filtering in the proposed method is over, the group processing signals from routing and reference stations is provided, in which NPEFE signals are selected in the context of pulse noise, which are simultaneously recorded by routing and reference stations. Indeed, the application of the group processing by setting admissible ranges of factor values for cross-correlations between the signals of the corresponding channels of different routing devices and signals between different routing and reference devices, the setting of time interval for calculation of the cross-correlations factors for signals and calculation of factors for cross- correlations between the signals of the corresponding channels of the routing and reference devices, and the comparison of each calculated cross-correlation factor for each routing device and the corresponding admissible ranges of factors for cross-correlation of signals with further determination of a signal of routing device as a NPEFE signal in the point of current location of the routing device, provided that the values of calculated cross-correlation factors correspond to the preset respective admissible range of cross-correlation factors, allow for the selection of 14 000093

NPEFE in the context of pulse noise, that makes it possible to record the NPEFE with higher quality in the context of that noise.

For the purpose above, the different routing and reference devices mean the same routing and reference devices that are used in the profiling when the claimed method is applied, and are those which differ by location in a certain period of time.

The group processing allows you to select NPEFE pulses precisely in the location of a routing device, from an aggregation of pulses, including both NPEFE pulses and pulse noises from local and remote sources.

The counting of a number of signals identified as NPEFE signals at each point of current location of the device is made for each corresponding routing device within a time interval corresponding to the preset discreteness of signal measurement, which is used to determine the intensity of NPEFE, the spatial change of which in the area of exploration is used area make a conclusion on geophysical anomalies in the explored profile, for mapping the boundaries of anomalies based on NPEFE intensity values at different points in the area of exploration, and to provide a geological interpretation of the results, thus making it possible to search and explore mineral resources, particularly oil and gas fields.

The claimed invention is illustrated by the following example of the geophysical exploration method and related drawings.

Fig 1 shows the block diagram of the device for recording NPEFE signals, depicting: 1 - routing device for recording signals; 2 - reference device for recording signals; 3 - group processing device; 4 - electronic computing machine (computer).

Fig.2 shows the block diagram of the device for recording signals, depicting

5 - channel for receiving magnetic component X; 6 - channel for receiving magnetic component Y; 7 - channel for receiving magnetic component Z; 8 - control device. 00093

Fig. 3 shows the block diagram of the channel for receiving magnetic component, depicting 9 - induction magnetometer; 10 - adjustable amplifier; 1 1 - analog-to-digital converter; 12 - channel microcontroller.

Fig. 4 shows the block diagram of the control device (prototype-based), depicting: 13 - control-oriented microcontroller; 14 - buzzer; 15 - start button; 16 - working device; 17 - clock; 18 - serial port controller; 19 - GPS.

Fig. 5 shows the block diagram of the device for group processing, depicting 20 - digital filtering microprocessor; 21 - group processing microprocessor; 22 - monitor; 23 - input device (keyboard).

Fig. 6 shows the change in signal intensity over time for 165 sec, recorded in the peg by the device designed on the example of the prototype (without the use of digital signal filtering). The change in the intensity is almost doubled due to the inclusion of a remote source of noise from 37 to 127 sec. CU (conditional unit) - the conditioning of an on-going number of pulses per second for the maximum value of a number of pulses per second for the period of exploration or among all pegs of the profile, or among all pegs in the area of exploration.

Fig. 6a shows the signal at the output of the channel receiving magnetic component over 165 sec. The interval of the signal amplitude change coincides with the interval of the intensity in Fig. 6. Horizontally - smpl - discrete in time (in this case, 6 microseconds), vertically - smpl - discrete in amplitude due to the value of least significant digit of the analog-to-digital converter (ADC).

Fig. 6b shows the spectrogram of the output signal from the channel receiving magnetic component over 165 sec. The interval of changes in the brightness of spectral components coincides with the interval of changes in the signal amplitude in Fig. 6a and in the intensity in Figure 6. Horizontally - smpl - discrete in time (in this case, 6 microseconds), vertically - smpl - frequency in Hz.

Fig. 7 shows the change in the signal intensity over 165 sec after using the digital signal filtering and subsequent calculation of intensities similar to the prototype. As a result, the noise components shown in Fig. 6, Fig. 6a and Fig. 6b are suppressed. CU (conditional unit) - the conditioning of an on-going number of pulses per second for the maximum value of a number of pulses per second for the period of exploration or among all pegs of the profile, or among all pegs in the area of exploration.

Fig. 8, 8b, 8c show the signal at the output of the channel receiving magnetic component before using the digital filtering (upper graphs in Fig. 8a, 8b, 8c) and after using the digital filtering (lower graphs in Fig. 8a, 8b, 8c). The right side of the figure has the fragments of signals which are strobed in its left side. Even visually you can see that the filtering resulted in occurrence of the pulses (lower graphs in Fig. 8a, 8c, 8c) which were hidden by the noise (upper graphs in Fig. 8a, 8b, 8c).

Fig. 9 shows the monitor of the device for group processing of simultaneously recorded signal by routing and reference devices within one interval of sampling. The signals from routing and reference devices, after the digital filtering (upper 8 lines), the correlations dependences between these signals (further 7 lines), the results of group analysis (the signal is identified as NPEFE by the pulse marked in the bottom line) and the number of pulses considered to be NPEFE at the selected sampling interval in the point of the routing device location.

Fig. 9a shows a kind of pulse noise simultaneously recorded by reference and routing devices (marked by strobe to the right).

Fig. 9b shows a kind of pulse noise simultaneously recorded by reference and routing devices (marked by strobe to the right).

Fig. 9c shows a kind of pulse simultaneously recorded by routing devices, which are the top two lines, and not recorded by routing devices, which are 3-8 lines (marked by strobe to the right). The pulse is referred to the NPEFE signal - the pulse in the bottom line at the beginning of the strobe.

Fig. 9d shows a kind of pulse simultaneously recorded by routing devices, which are the top two lines, and not recorded by routing devices, which are 3-8 lines (marked by strobe to the right). The pulse is referred to the NPEFE signal - the pulse in the bottom line

Fig. 9e shows a kind of pulse simultaneously recorded by routing devices, which are the top two lines, and not recorded by reference devices, which are 3-8 lines (marked by strobe to the right). The pulse is referred to the NPEFE signal - the pulse in the bottom line.

Fig. 10 shows the change in the intensity along the profile laid across the structural heterogeneity. The origin of coordinates coincides with the intersection of the profile and a priori known structural heterogeneity (Fig. l l b shows a priori known structural heterogeneity as a tectonic disturbance) identified by the results of seismic studies. In addition, the simultaneous recording by routing and reference devices, the digital filtering and the group processing were provided according to the claimed method. CU (conditional unit) - the conditioning of an on-going number of pulses per second for the maximum value of a number of pulses per second for the period of exploration or among all pegs of the profile, or among all pegs in the area of exploration.

Fig. l 1 , l ib show the exploration plans for Verkhnii Maslovets Field: (a) general plan; (b) plan for profile area.

The graphic materials which illustrate the claimed invention, the presented option of how to use the method and the example of how method may be realized do not limit the scope of the claims set forth in the formula, but only to explain the essence of the invention.

The geophysical exploration method may be applied using the device for recording signals which contains, like in the prototype, the channels for receiving and converting analog signals, the control unit that contains control microcontroller, the clock and the navigation positioning system.

According to the invention, the device for recording NPEFE (Fig. 1) contains at least two routing devices for recording signals 1 and at least two reference devices for recording signals 2 and the device for group (collective) processing the information 3 from all routing and reference devices involved in the recording. In addition, the device for group (collective) information processing 3 is connected to the computer 4. Each device for data recording 1 and 2 (Fig. 2) has at least two channels for receiving magnetic component, and in this option of realization it has three reception channels: 5 - channel for receiving magnetic component X, 6 - channel for receiving magnetic component Y, 7 - channel for receiving magnetic component Z, and also the device for information recording includes the control unit 8.

Each channel for receiving magnetic component 5, 6, 7 (Fig. 3) of the device for recording signals 1 , 2 has the induction magnetometer 9, the adjustable amplifier 10, the analog-digital converter 1 1 and the channel microcontroller 12, which are connected in series The adjustable amplifier 10 is connected to the channel microcontroller 12.

The control unit (Fig 4), like in the prototype, has the control microcontroller 13 connected to the start button 15, the clock 17, the buzzer 14 and the controller serial port 18, which is connected to the GPS-navigator 19, and to the storage device and the clock. The control microcontroller is connected with each channel group and the device for group processing.

The device for group processing (Fig. 5) has the microprocessor for digital filtering of 20 signals received from devices recording signals 1 , 2 (routing and reference devices), from the output of which signals comes to the input of the microprocessor for group information processing 21. In addition, the microprocessor for group processing 1 1 is connected to the microprocessor of digital filter 20, the monitor 22, the keyboard 23, the computer 4 and control microcontrollers 8 of the devices for recording signals by standard communication channels.

The automatic digital filtering which uses the wavelet analysis of the output signal of each channel is applied to suppress narrowband disturbances that appear as peaks in the signal spectrum. Fig. 6, 6a, 6b, 7, 8a, 8b, 8c show the signals received by devices without using the digital signal filtering and with using the digital signal filtering. It is evident that the digital filtering reduces the level of disturbances and causes the occurrence of the pulses (lower graphs in Fig. 8a, 8b, 8c) which were hidden by the noise (upper graphs in Fig. 8a, 8b, 8c).

Thus, the use of the digital filtering allows you to even visually see much better selection of signals in the context of narrowband noise.

Then, the group information processing which is based on the selection, from the variety of signals simultaneously received by routing and reference devices, of those signals which are received only by routing devices 1 located in the analyzed peg and, therefore, are not received by all reference devices 2 and routing devices 1 in other pegs, and the subsequent recording of their intensity in the analyzed peg (counting of the number of those signals in selected sampling interval).

As a measure of similarity (difference) of signals simultaneously received by devices, a factor of cross-correlation between those signals is used.

The background for group processing is as follows:

- signals from all routing and reference devices involved in the group processing that have been digitally filtered (for selection of signals in the context of noise);

- pre-set discreteness of polling devices (time interval during which the intensity of NPEFE signals is calculated);

- pre-set time interval to calculate factors for the cross-correlations of signals;

- set allowable ranges for cross-correlation factors to take a decision on similarity (difference) of the compared signals (ranges of similarities/differences);

- set maximum possible time for distribution of signals among routing and reference stations

The following sequence of basic operations for the group processing of each analyzed peg: 1. Considering the specified time interval to calculate cross-correlation factors, the factors of cross-correlations of signals among routing devices 1 located in the analyzed peg are calculated, and:

- routing devices 1 located in the analyzed peg and

- routing devices 1 located in adjacent pegs;

- reference devices 2 to compensate disturbances from local sources in the vicinity of the area being explored;

- reference device 2 to compensate disturbances from remote sources,

2. The value of each calculated cross-correlation factor is compared with the values of corresponding specified admissible ranges of cross-correlation factors for making a decision on similarity (difference) of the compared signals

3. When all calculated cross-correlation factors simultaneously fall into in the corresponding preset ranges of similarities/differences, a decision is made that the analyzed signal is received only by routing devices 1 located in the analyzed peg and the signal from the analyzed routing device is considered as a NPEFE signal in that peg, and the same signal is included in calculation of the NPEFE intensity.

4. These operations are repeated during the time interval that corresponds to the preset discreteness of devices polling.

Thus, during the group processing of the information recorded simultaneously by routing and supporting devices 1 , 2, for each peg, a calculation is made for the factors of cross-correlations between the simultaneously received signals from the corresponding channel of the routing devices 1 located in the analyzed peg and the routing devices 1 located in the analyzed peg, and:

- routing devices 1 located in adjacent pegs;

- reference devices 2 to compensate disturbances from local sources in the area of exploration;

- reference devices 2 to compensate disturbances from remote sources.

For each peg, a signal from routing devices 1 which correspond to that peg is identified as the NPEFE signal in the peg, provided that the value of the calculated cross-correlation factors of the signals correspond to the previously specified ranges. As already mentioned above, the following ranges are set for area of exploration:

0.7...1 - range of similarity;

(-0.3)... (+0.3) - range of differences.

Further, for each peg within a time interval that corresponds to the preset discreteness of devices polling, a number of signals identified as NPEFE signals (intensity of NPEFE) is counted.

Fig. 9, 9a show the monitor of the device for group processing of the information from routing of reference stations.

Fig. 9a, 9b show that the pulse noise (the pulse received simultaneously by routing and reference devices - it is presented in the figure in the respective signal lines) is identified as a NPEFE signal (no pulse in the last line).

Fig. 9c, 9d, 9e show that the pulse received only by route device is the NPEFE signal (the respective pulse is in the last line).

Thus, the use of group processing allows for filtering NPEFEs in the context of pulse noise, making it possible to record NPEFEs in the context of that noise.

The group processing allows selecting NPEFE pulses in the point of current location of the routing device being analyzed from the aggregation of pulses, including both NPEFEs and noise pulses from local and remote sources.

After the group processing of all pegs, the recorded intensities of NPEFE and the coordinates of the corresponding pegs are coming to the computer 4 for the subsequent processing by special programs to construe the changes of dependence of the NPEFE intensity the area of exploration, map the boundaries of anomalies and give a geological interpretation of the results.

The recorded NPEFE intensities and the coordinates of the corresponding pegs allow for establishment of dependence changes in the NPEFE intensities and construction of the corresponding graphs. In addition, the resulted data are used for mapping the boundaries of geophysical anomalies as one of the exploration 2014/000093 methods. The results of the mapping are used to prepare geologic maps that form the basis for searching for hydrocarbons such as oil and gas.

The geological interpretation of geophysical data is based on the determinate relationships of geophysical anomalies with geological factors (structures of certain types and sizes, composition of different rocks and concentrations of minerals) and provided by the method known to experts in the field.

The example of profile measurements in the Verkhnii Maslovets Field near the village of Skhidnytsya in Lviv Region is following.

The first four recording devices were located at the same distance of 1 meter in the peg in the area of the intersection of the explored profile and a priori known structural heterogeneity determined by the results of seismic studies. Another pair of devices was installed at a distance of 15 km from the explored profile as references for recording signals from remote sources of disturbance. The fourth pair of devices for recording signals was consistently moved to the area of local sources of man-made disturbances in the vicinity of the explored profile. Moreover, the simultaneous recording of signals by all devices was conducted for each location of the fourth pair of devices (each source of man-made disturbance)

Before the simultaneous recording of signals by the said devices, the magnetometers 9 of the channels receiving magnetic component 5 of all the devices for recording signals were oriented in the same specified directions of space using a compass. The start button 15 was used to turn on all the devices at the standard time signal, using the clock. Within five minutes, the signals were recorded by all devices for each location of the fourth pair of devices (each source of man-made noise). The recorded information was loaded into the computer, in which it was processed by a special program, and the information about the change in time of the amplitude of signals recorded simultaneously by all the devices and the change in time of cross-correlation of signals in the area of man-made noise sources and in the peg of the explored profile was displayed simultaneously on the monitor. This known correlation helped to get more accurate identification of signal from the devices located on the profile and near the source of man-made disturbances. Those sources of man-made disturbances, the signals from which exceed the specified threshold in the peg of profile were considered meaningful (those which require installation of reference devices 2 in their area).

The results of that analysis were used to refine the locations for installation of reference devices 2 in the vicinity of local sources of disturbances. As a result, before recording the signals for the profile exploration, the two recording devices, as reference ones, were installed at the significant source of the local man-made noise (the powerful transformer substation at a distance of 2 km from the explored profile). The two reference devices for recording signals from remote sources of noise were located at a distance of 15 km from the explored profile. The two pairs of routing devices were installed at the same distance of about one meter in the area of the intersection of the explored profile and a priori known structural heterogeneities determined by the results of seismic studies. The magnetometers 9 of the channels receiving magnetic component 5 of all the devices for recording signals were oriented in the same specified directions of space using a compass. The start button 15 was used to turn on all the devices at the standard time signal, using the clock. Within three minutes, the simultaneous recording of signals was effected by all the devices.

Then, the two routing devices 1 were moved and installed in the peg at the beginning of the explored profile, while the magnetometers 9 of the channels receiving magnetic component 5 of all the devices for recording signals were oriented in the same specified directions of space using a compass. The rest of the routing and reference devices were left in the selected locations and the continuous recording of signals was provided during the profile exploration. With this arrangement, the simultaneous recording of signals by all reference and routing devices was made within three minutes. To do that, the standard time signal was used for additional synchronization of all reference and routing devices.Later on, the two routing devices 1 were step by step moved from one peg to another along the explored profile. In this case, after installing them in each peg, the simultaneous recording of signals was taken by the routing and references devices within three minutes, similarly to those measurements which were taken at the beginning of the profile.

After recording the signals in all pegs, the information from all reference and routing devices was loaded into the computer 4, and processed by special programs to construct the change in the NPEFE intensity along the explored profile.

Fig. 10 shows the change in the intensity dependence of NPEFE along the analyzed profile. Figure 10 also shows an anomalous decrease in the intensity in the area of the intersection of the explored profile and a priori known structural heterogeneity determined by the results of seismic studies. This illustration shows the operability of the proposed method.

Thus, the proposed method can improve the efficiency of detection and mapping of structural and lithological heterogeneities of the crust on the basis of measurements of the natural pulsed electromagnetic field of the Earth: geologic faults and places of their crossing, cracks, boundaries of dissimilar rocks and hydrocarbon traps. This is achieved by increasing the efficiency of the selection of NPEFE pulses of local origin, the parameters of which convey the information about the geophysical structure of the area being explored, in the context of background disturbances from local (located in the area of exploration and in its immediate vicinity) and remote sources, including natural disturbances of (atmospheric and lithospheric) origin.

Claims

1. The geophysical exploration method which involves synchronous measurements of an intensity of the natural pulsed electromagnetic field of the Earth (NPEFE) in different parts of the area being explored with all measurements are taken in a range of very low frequencies in at least two different directions to receive a signal by routing and reference devices, and first the sensitivity and identity of reception of signals by all routing and reference devices are adjusted, the antennas for the same reception channels of all involved devices are oriented in same preset directions of space, the graphs with spatial changes in the intensity of fields along the work profile are construed, any geophysical anomaly is identified in the profile being explored, with measuring available structural and lithological heterogeneities by an anomalous change in the intensity of NPEFE, the boundaries of anomalies are mapped and the results are given a geological interpretation, characterized in that the routing devices for measurement of the electromagnetic field for subsequent compensation of noises from local and remote sources are additionally installed, at least two routing devices are installed in each peg, the profiling is made with simultaneous measurement of signals by all routing and reference devices with the preset discreteness, the digital filtering is provide for selection of signals in the context of noise, the group processing is given to signals from routing and reference devices by setting admissible ranges for factors of cross- correlations between signals of the corresponding channels of different routing devices, different routing and reference devices, a time interval is set for calculations of factors of cross-correlations for signals, calculations of factors of cross-correlations between signals from the corresponding channels of routing devices and between signals of the corresponding channels of routing and reference devices, values of each calculated factor of cross-correlations for each routing devices are compared with corresponding admissible ranges of factors for cross-correlations of signals, with further determination of a signal from the routing device as a NPEFE signal in the point of current location of the routing device, if the values of the calculated cross-correlation factors correspond to the preset corresponding admissible range of cross-correlation factors, then a number of signals determined as NPEFE signals is calculated in each point of current locations of the corresponding routing device for each corresponding device within the time interval in accordance with the preset discreteness of signal measurements, and the intensity of NPEFE in those points is determined for the further mapping of the boundaries of geophysical anomalies, on the basis of the intensity value of NPEFE in different points of the area being explored.