RU1822996C - Nuclear-magnetic logging unit - Google Patents

Abstract

Usage: in geophysics in the study of oil and gas wells. SUMMARY OF THE INVENTION: a measuring sensor is included in a calibration circuit, for which purpose a generator of a signal with a stable amplitude signal with a frequency equal to the frequency of free precession, and communication resistors, and a switch providing alternating connection of the measuring sensor to a polarization current source are introduced into the device measuring amplifier, connects a stable signal generator to the measuring sensor connected to the input of the measuring amplifier through communication resistors. The output signal in this mode is proportional to the transmission coefficient of the entire receiving-measuring path, including the measuring sensor. 3 ill.

Description

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The invention relates to field geophysical studies, and more particularly, to the technique of nuclear magnetic logging of oil and gas wells.

The aim of the invention is to remedy this drawback of known devices by including in the calibration path all the elements of the receiving and measuring path, including the measuring sensor.

In FIG. Figures 1 and 2 show block diagrams of the device without and in the presence of a calibration sensor; Fig. 3 is a diagram illustrating their operation.

The proposed device (see Fig. 1) includes a borehole part 1, the units and elements of which are placed in a sealed housing (not shown), made at least partially of non-magnetic and non-conductive materials, a ground part 2 and a wireline cable 3 connecting them.

acting as a support cable and communication line.

Downhole part 1 includes a measuring sensor consisting of a solenoid coil 5 connected in parallel, the axis of which is perpendicular to the axis of the well, and a capacitor 6 forming a resonant circuit tuned to the frequency of the free procession of hydrogen atoms in the Earth's magnetic field; a polarization current source 7 (which, in principle, can be placed in the ground part 2 of the device); measuring differential amplifier 8 with a soft-start circuit (not shown), an amplitude-stable signal 9 with a frequency equal to the frequency of free precession of hydrogen atoms in the Earth’s magnetic field, with symmetric paraphase output coupling resistors 10 and 11. connected to generator output 9; comm00

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tator 12 with three groups of keys 12A. 12V 12C; the control unit 13 of the switch 12, as well as the borehole telemetry unit 14 and the downhole power supply 15 connected to the logging cable 3. The ground part 2 of the device includes a ground telemetry unit 16 connected to the logging cable 3, the signal processing and analysis unit 17, the recorder 18 and ground power supply 19..

The device in the presence of a calibration sensor, shown in figure 2, includes in addition to these nodes a calibration sensor 20, made, for example, in the form of connected in parallel with a toroidal coil 21, in the cavity of which is placed an ampoule with a reference hydrogen-containing liquid 22, and a capacitor 23, forming a resonant circuit tuned to the frequency of free precession of nuclei of hydrogen atoms in the Earth's magnetic field. The switch 12 in this embodiment of the device is made with 4 groups of keys 12A, 12B, 12C, 12D, providing a choice of measuring 4 or calibration 20 sensors.

The proposed device operates as follows.

The control unit 13 of the switch 12 connects the measuring sensor 4 through the keys 12A to the output of the polarization current source 7 (mode A in diagram 24 (Fig. 3), while the magnetic field of the current flowing through the coil 5 of the sensor 4 polarizes the magnetic moments of the atoms hydrogen in the adjacent volume of rocks parallel to the axis of the coil 5; after polarization is completed, the control unit 13 of the switch 12 connects the measuring sensor 4 to the input of the measuring amplifier 8 via keys 12B (mode B in diagram 25 in Fig. 3) and the signal excited in 4, the magnetic moments of the precessing nuclei of hydrogen atoms in the rocks after its amplification by the amplifier 8 passes through the telemetry systems 14, 3, 16, processing and analysis, in block 17 is registered by the registrar 18; after the registration of the free precession signal, the control unit 13 of the switch 12, through the switches 12C, connects the generator 9 through the coupling resistors 10 and 11 to the measurement sensor 4, which through the switches 12B remains connected to the measurement amplifier 6 (mode C in diagrams 25, 26 of FIG. 3), and the signal of the generator is recorded ora 9, passing through all the elements priemoizmeritelnogo path 4, 8, 14, 3, 16, 17. Then the calculated ratio of the signal recorded in the mode B (UB). to the signal registered in pe0

5

0

Ur

press C (Uc). The ratio R gives a relative estimate of the signal amplitude of the free precession of hydrogen atom atoms in the rock, free from the influence of changes in the parameters of all elements of the receiving-measuring path, including measuring sensor 4.

The second variant of the device (see Fig. 2) involves conducting at each well point two similar measurement cycles described above, in the first of which (modes A. B, C in diagram 24, 25. 26 of Fig. 3), a measuring sensor 4 is used. and in the second (modes A. B, C in diagrams 27, 25, 26 of Fig. 3), a calibration sensor 20. The sensor is selected by the control unit 13 of the switch 12 through the keys 12E. According to the results of measurements in the first cycle, youUB

the parameter R

Uc

, and by result 5

0

5

0

5

0

5

there measurements in the second cycle - parameter UB

R

WE

. Then calculate the ratio

R / R, which gives an estimate of the relative amplitude of the free precession signal associated with the mobile fluid in the rocks, free from the influence of changes in the parameters of all elements of the receiving and measuring path, as well as from the orientation of the borehole part of the device relative to the Earth’s magnetic field.

The calibration signal of the sensor 20, in addition, as in known devices, can be used to control the frequency of free precession of hydrogen atoms in the Earth's magnetic field, which allows frequency tuning of both the elements of the receiving amplifier path and the stable signal generator 9.

Using the proposed device, in comparison with the known one, it is possible to increase the accuracy of estimating the signal level of the free precession and, accordingly, the reservoir rock parameters by taking into account the influence of changes in the parameters of all elements of the receiving-measuring path, including the measuring sensor.

Claims (1)

SUMMARY OF THE INVENTION A nuclear magnetic logging device comprising a borehole part consisting of a measuring sensor including a solenoid coil, the axis of which is perpendicular to the axis of the borehole part, and a capacitor connected in parallel therewith, forming a resonant circuit tuned to the frequency of free precession of hydrogen atoms in the magnetic Earth field, current source polarization, downhole power supply, differential measuring amplifier, control unit and switch, including the first, second and third key pairs, the control inputs of each of which are connected to the first and second outputs of the control unit, the inputs of each of the first and second key pairs are connected parallel to the outputs of the measuring sensor, the outputs of the first key pair are connected to the outputs of the polarization current source, and the outputs of the second pair of keys are connected to the input of a differential measuring amplifier, the output of which The downhole telemetry unit and the communication line are connected to an extraterrestrial part containing a processing and analysis unit, a recorder, and also ground power and telemetry units, characterized in that, in order to increase the accuracy of measurements, the account of changes in the parameters of all elements of the receiving-measuring path, including the measuring sensor during the measurement, additionally contains a generator of a signal stable in amplitude with a frequency equal to the frequency of the free precession atomic hydrogen signal in the Earth’s magnetic field, made according to the scheme with a symmetric paraphase output, the first and second communication resistors, the inputs of the third pair of switch keys are connected to the second terminals of the first and second communication resistors, the outputs are connected to a measuring sensor, and the input The control wires are connected to the third output of the control unit, the first terminals of the first and second communication resistors are connected to the output of a generator with a stable amplitude signal, and the fourth output of the control unit is connected to the downhole telemetry unit. Figure 1 FIG. 2