SU1296973A1 - Reception device for low-frequency electric surveying - Google Patents

Abstract

The invention relates to electrical exploration methods for the study of mineral deposits and can be used, in particular, in downhole electrical exploration methods. The purpose of the invention is to increase the accuracy of measurements of a low-frequency electric field in wells with poor grounding conditions. The goal is achieved by introducing a known receiving device containing a hollow working electrode that compensates for a hollow electrode and an antenna amplifier located between them, an additional working electrode compensating the electrode and the antenna amplifier . In addition, a high-pass filter, a high-frequency master oscillator, a modulator, a buffer stage, a demodulator, and a ground-band controller — a band-pass filter and a detector are introduced into the downhole tool. In addition, two feedback circuits for the carrier frequency and for the high-frequency oscillation envelope are introduced into the modulator, and the working electrodes are made in the form of replaceable cylinders, 1 hp. f-ly, 2 ill. (L CO 05 CO CO

Description

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11296973

The invention relates to electrical exploration methods for the study of mineral deposits. An advantageous area of its application is borehole electroprospecting methods, in which a low-frequency electric field is measured.

The purpose of the invention is to improve the measurement accuracy of a low-frequency electric field in dry wells. ABOUT

FIG. 1 shows a block diagram of the proposed device; 2 is a block diagram of a modulator used in the device.

The device contains two hollow working electrodes 1.1 and 1.2, filled with a conductive material, such as metal, two hollow compensating electrodes 2.1 and 2.2, located in the space between the antennas 3.1 and 3.2 and the working electrodes. The working electrodes are connected to the inputs of antenna amplifiers. The antenna amplifiers are interconnected by a two-wire line 4. A transformer 5 is connected to one of the branches of the two-wire line 4, and hollow compensating electrodes are connected to the ends of the other branch.

thirty

A communication transformer is connected to the input of the selective amplifier 6, the output of which is connected to the low-frequency input of the modulator 7. To the high-frequency input of the modulator 7 via a buffer stage 8 connects a high-frequency master oscillator 9. The output of the modulator by a two-wire symmetrical line 10 passing through one of the hollow compensating electrodes and the corresponding working electrode is connected to the input of the high-pass filter 11. Blocks 1 through 11 are structurally incorporated into the downhole tool. The filter loads a wireline 12 connected to a surface console. The cable is directly connected to the input of the bandpass filter 13 and the demodulator 14, the output of the demodule of the measuring line with the source of the received signal. Since structurally working electrodes are cylinders of conductive material located on the body of an downhole tool made of an insulator, it is advisable to increase the diameter of the electrode to reduce the impedance of the electrodes. Constraints here arise in connection with providing the necessary technological gap between the borehole wall and the electrode. As the calculations show, the difference in the diameters of the well and the working electrode should not exceed 10 mm.

Since the gain of the antenna amplifier is close to one and the amplifier itself is a broadband device, it does not transform the spectrum of the received signal. In practice, an antenna amplifier serves to match the high resistance of the working electrode with the low resistance of subsequent blocks of the device.

Due to the fact that the antenna amplifiers are interconnected by a symmetric line, the pickups to each of the branches are the same and in the transformer 5 the links are subtracted. The compensation of parasitic capacitive leakage is also due to compensating electrodes. The length of the communication line between the electrodes is determined by the required .35 spacing of the working electrodes. But to maintain the pointlike nature of the electrodes, the distance between the electrodes must be at least three times their length:

40 Thus, at the output of the transformer 5, a signal equal to the difference of the signals induced on the working electrodes will act. In the electoral amplifier 6, 45 filtering and amplification of the low-frequency signal f ...

then you

Subsequently, the signal arrives at the low-frequency input of the modulator. The torus is connected to the detector 15 and the reti-y) frequency-frequency modulator input with the sweeping device of the 16. giving generator 9 through a buffer

Fig. 2 shows a scheme of modulo-cascade 8, a signal from a high-speed clock 7 with negative feedbacks. low f | (block 17) and high f (block 18) frequencies.

The device works as follows.

Due to the capacitance of the working electrodes on earth, communication is carried out

 to

As a result, there are three frequencies f, f 1 ± f in the signal spectrum at the modulator output.

The modulated signal via a two-wire line, including inside the hollow compensating and antenna electrodes, goes to the filter

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0

ABOUT

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measuring line with the source of the received signal. Since structurally working electrodes are cylinders of conductive material located on the body of an downhole tool made of an insulator, it is advisable to increase the diameter of the electrode to reduce the impedance of the electrodes. Constraints here arise in connection with providing the necessary technological gap between the borehole wall and the electrode. As the calculations show, the difference in the diameters of the well and the working electrode should not exceed 10 mm.

Since the gain of the antenna amplifier is close to one and the amplifier itself is a broadband device, it does not transform the spectrum of the received signal. In practice, an antenna amplifier serves to match the high resistance of the working electrode with the low resistance of subsequent blocks of the device.

Due to the fact that the antenna amplifiers are interconnected by a symmetric line, the pickups to each of the branches are the same and in the transformer 5 the links are subtracted. The compensation of parasitic capacitive leakage is also due to compensating electrodes. The length of the communication line between the electrodes is determined by the required .35 spacing of the working electrodes. But to maintain the pointlike nature of the electrodes, the distance between the electrodes must be at least three times their length:

40 Thus, at the output of the transformer 5, a signal equal to the difference of the signals induced on the working electrodes will act. In the electoral amplifier 6, 45 filtering and amplification of the low-frequency signal f ...

then you

cascade 8 is given a high-frequency signal

 to

As a result, there are three frequencies f, f 1 ± f in the signal spectrum at the modulator output.

The modulated signal via a two-wire line, including inside the hollow compensating and antenna electrodes, goes to the filter

11 high frequencies, the bandwidth of which is chosen in such a way that it transmits without distortion the modular signal, i.e. frequency f., f

about b

and cuts off the low-frequency part of the spectrum.

Then, via cable 12, the signal enters the input of the band-pass filter 13, which is structurally an element of the surface part of the apparatus. In general, the signal conversion and filtering system using filters 11 and 13 allows one to get rid of possible electromagnetic interference from extraneous sources as well as

operating frequency signal f., which

to

cable 12, the length and brand of which can be different, and therefore, the modulator must operate stably for different loads. In order to fulfill the above requirements, the modulator introduced two feedback loops at the carrier frequency f, and

high frequency oscillation L.

If only one feedback loop is used, a large magnitude of the coupling coefficient will cause the system to become excited at the corresponding frequency.

The use of two f5 circuits simultaneously allows one to create a system with deep feedback, in which the expansion of the dynamic diapason, the improvement of linearity, the reduction of the dependence of parameters on the log is brought to the logging station.

As already noted in the cab, taking into account the long cable length and its possible proximity to the source of the working signal 20 of the load, occurs when comparing (for example, when working in a version of extremely weak feedback links), the amount of signal induced on the cable can transcend the signal coming from the electrodes. The application in similar cases in geophysical equipment for transmitting a useful signal with the transformation of its spectrum has long been known (for example, in equipment of radio wave meters). There, the principle of superheterodyne reception is used, and the corresponding blocks are used in the device.

Taking into account the low frequency spectrum of the working signal, namely hundreds, and

40

In the perspective of ten Hz, the use of a 35 VA instrument was developed, allowing superhero herdin reception to be almost impossible. The latter circumstance is explained by the fact that with a small intermediate frequency and its proximity to the operating frequency, the requirements for signal filtering blocks increase dramatically, which is difficult or impossible to achieve in the dimensions of downhole tools at low frequencies. The narrowing of the signal path bandwidth, in addition, if necessary, should lead to an increase in the requirements for frequency stability of the sources of working signals, i.e will cause difficulties in creating generating devices that will be used simultaneously with the proposed receiver.

Considering that the range of variation of the operating signal is large, the modulator is subject to increased requirements with regard to dynamic range and linearity. In addition, from the device circuit itself, it follows that the modulator, through filter 11, is connected to the

measure the low-frequency electric field in the well. The advantages of such a device are obvious when working in conditions of wells covered in permafrost conditions, in mountains, in underground mines, i.e. where dry wells are found in large numbers.

Claims (2)

1. Receiver for low-frequency electrical prospecting, containing at least one hollow metal working electrode, antenna preamplifier compensating a hollow electrode located in the space between the antenna preamplifier and the working electrode, a selective amplifier whose detector is connected to a measuring device , characterized in that, in order to increase the measurement accuracy in wells with poor conditions, 55 cable 12, the length and brand of which can be different, and therefore, the modulator must operate stably for different loads. In order to fulfill the above requirements, the modulator introduced two feedback loops at the carrier frequency f, and high frequency oscillation L. If only one feedback loop is used, then a large value of the coupling coefficient will cause the system to become excited at the corresponding frequency. The use of two 5 circuits simultaneously allows one to create a system with deep feedback, in which the expansion of the dynamic diapason, the improvement of linearity, the decrease in the dependence of parameters on the load magnitude, occurs at relatively weak feedback links for high and low frequency, i.e. guarantee the inability to self-excitement. I Ground signal operations the control panel flows out of the previous one. The signal is amplified, if necessary, after the band-pass filter 14 and enters the demodulator, where it is converted into a signal of the operating frequency f. The signal goes to the detector and the measuring device. Based on the proposed device Your device was designed to allow measure the low-frequency electric field in the well. The advantages of such a device are obvious when working in conditions of wells covered in permafrost conditions, in mountains, in underground mines, i.e. where dry wells are found in large numbers. 35 WA device was developed allowing 45 claims Your device was designed to allow 1. Receiver for low-frequency electrical prospecting, containing at least one hollow metal working electrode, antenna preamplifier compensating a hollow electrode located in the space between the antenna preamplifier and the working electrode, a selective amplifier whose detector is connected to a measuring device , characterized in that, in order to increase the measurement accuracy in wells with poor conditions ground, for example, dry, an additional nor- mal metal working electrode, an antenna preamplifier, a compensating hollow electrode located between the antenna preamplifier and a working electrode, a high-frequency driving oscillator, a buffer cascade are introduced into the device; modulator and high-pass filter, and the connection between the two working electrodes is made in the form of a symmetrical two-wire line, in one of the branches of which a communication transformer is connected, the secondary winding of which is connected via a selective amplifier to the low-frequency input of the modulator, one output of the modulator is connected to the input of the high-pass filter symmetrical two-wire line, a VNIIPI Order 774/48 Circulation 731 Subscription Proizv.-polygr. pr-tie, Uzhgorod, st. Project, 4 a high-frequency master oscillator is connected to the high-frequency input of the modulator via a buffer cascade, and the output of the high-pass filter is connected via a logging cable to the ground control panel. connected to the detector input. 2. The device according to claim 1, characterized in that, in order to increase the measurement accuracy by reducing the grounding resistance, both working electrodes are made in the form of replaceable cylinders of different diameters.