SU184360A1 - L. Ya. V.M. Timofeev and A.A. VakulskyMizyuk, 'I! "” - -; - -' IVu '• *' '•; • ^ - "T '. -I h, t -.'--- .- ^'" - - Google Patents

Description

The invention relates to the field of inductive geoelectrical exploration in the vicinity of boreholes and is intended for carrying out work using the transient processes in the borehole variant (SMPT).

Apparatus for the induction investigation of the vicinity of a well is known, comprising an ungrounded loop on the surface and a magnetic field sensor lowered into the well. These devices using harmonic fields have a limited range and are not used in cased wells.

Also known are devices for recording transients in an inductively excited magnetic field, used in terrestrial and aeropaths.

The proposed device is different in that in its generator part a relay is switched between the powerful key and the generator loop, switching the ends of the loops in the pauses between the unipolar current pulses, and in the measuring part between the output of the strobe pulse multivibrator and the gating keys are included the last control schemes that measure signal of both polarities.

An additional compensation frame is connected to the output of the measuring part, coaxially with the receiving one, with a distance of m between them no more than 1/5 the distance from the center of the system.

frame to the generator loop on the surface, which has increased the level of the useful signal relative to the residual signal from eddy currents in the casing and the manufacturer of the measurement in the cased

well.

FIG. 1 shows a block diagram of the generator part of the device; in fig. 2 is a block diagram of the measuring part of the device. The generator part consists of the master

multivibrator 1, control circuit 2, power switch 3, relay 4, generator loop 5, delay multivibrator 6, trigger 7 and emitter follower 8. The measuring part contains the receiving

frame 9 and additional compensation frame 10, preamplifier 11, matching cascade 12, input key 13, impulse amplifier 14, keys gated 15 and 16, storage device 17, DC amplifier 18,

arrow indicator 19, delay multivibrator 20, strobe pulse multivibrator 21, trigger 22 and two coincidence circuits 23 and 24.

The rectangular pulses of the multivibrator are fed to the control circuit 2 by key 3. The negative polarity pulses coming from the control circuit transfer the triode of key 3 to the saturation region and the entire supply voltage is applied to the generator loop 5. In the remaining time intervals, there is practically no current in the loop.

The clock pulses from the control circuit 2 are fed to the measuring device. For switching the loop ends, there is a multivibrator of delay 6, trigger 7, an emitter repeater 8 and relay 4. The multivibrator of delay 6 produces a pulse longer than the maximum delay time of the strobe pulse, which can also be used to measure the transient signal. Such a pulse duration is chosen in order to eliminate the interference occurring at the moments of switching the ends of the loop. The rear edge of the pulse of the half-wave multivibrator 6 triggers the trigger 7, which controls the operation of the emitter follower 8, the load of which is the winding of the relay 4, which switches the ends of the loop 5.

The measuring part of the device (see Fig. 2) provides a measurement of the unsteady signal by gating it with a time shift, the value of which is determined by the delay multivibrator 20, and the width by the strobe pulse multivibrator 21. The signal amplified by the preamplifier 11 from frames 9 and 10 is fed through a matching cascade 12 to the input key 13, which cuts out short transient pulses from the transient process, shifted by a certain time relative to the falling edge of the pulse in frame 9.

From the output of the key 13, the signal clippings arrive at the low-frequency amplifier 14 and further on the two keys 15 and 16, which are switched on alternately in such a way that each of them switches the signal of one polarity. The keys 15 and 16 are the elements of the storage device 17, made according to the synchronous filter circuit. The signal from the storage device 17 is additionally amplified by a DC amplifier 18. A transistor amplifier according to the modulator - amplifier - demodulator scheme is used as such an amplifier. The readings are recorded by an arrow indicator 19. The keys 13, 15 and 16 are controlled by using the multivibrator delay 20, the multivibrator of the pulse 21, the trigger 22 operating in the frequency division mode by two and two coincidence circuits 23 and 24.

The synchronizing pulses from the output of the control circuit 2 (see Fig. 1) arrive at the multivibrator delay 20 and the trigger 22. The multivibrator delay 20 is started at times corresponding to the current off in the generator loop 5, and produce pulses of a fixed duration. The falling edge of the pulse of the multivibrator delay 20 triggers the half-wave multivibrator of the strobe pulse 21, producing a short pulse of constant duration. This pulse simultaneously turns on the input key 13 and enters the matching circuits 23 and 24. The input key 13 cuts the transient signals both with positive and negative pulses of the exciter floor, which then goes to the pulse amplifier 14, the output of which is distributed pulses on a temporary basis on two channels. One channel receives pulses generated from a signal from a positive current pulse in the exciting loop, and from another, from a negative one. Such a time distribution is made by appropriately inserting keys 15 and 16. From the point of view of an increase in the useful signal containing information about the object under study, to a signal from an unsteady field of eddy currents in a casing string, it is very important to place the receiving and compensation frames de device) relative to each other and relative to the source gender. Experimental studies have shown that this ratio is maximal if, when the two frames are coaxially disposed, the distance between them is significantly less (within 1/5) the distance from the center of the frame system to the generator loop on the surface and is comparable to the distance from the borehole axis to the desired object. In this case, the signal from the eddy currents in the casing in both frames is almost the same and therefore is best compensated, and the signal from the target object is practically not reduced.

Subject invention

1. A device for geoelectromagnetic exploration of borehole surroundings using a transient method, consisting of a generator part containing a current source, a powerful key, a generator loop, and a receiving one containing an induction receiving frame, amplifiers, synchronization and pulse shaping circuits, accumulators and a recorder, that, in order to improve measurement accuracy, a relay is switched on in the generator part between the powerful key and the generator loop, switching the loop ends in the pauses between current pulses, and in the meter the second part between the output of the multivibrator pulse generated and key matcher includes gating circuits controlled guides the latter in the measurement signal of both polarities.

From eddy currents in the casing when measuring in a cased well, an additional compensation frame is connected to the output of the measuring part, coaxially with the receiver, with a distance between Pim no more than 1/5 of the distance from the center of the frame system to the generator loop on the surface.

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