RU90225U1 - NUCLEAR MAGNETIC LOGGING DEVICE - Google Patents

Abstract

1. A nuclear magnetic logging device comprising a downhole tool, consisting of a NMR sensor, a measurement, control, and tuning circuit associated with ground-based equipment consisting of a polarization current pulse generator and a measurement unit, using a wireline cable, a processor, characterized in that the processor is located inside the downhole tool and is connected to the NMK sensor and the measurement, control and tuning circuit. ! 2. The device according to claim 1, characterized in that the NMR sensor is configured to tune to a resonant frequency in the range up to 400 Hz.

Description

The invention relates to field geophysics and can be used to study drilled oil, gas and hydrogeological wells by nuclear magnetic logging in the Earth’s field.

A known method of obtaining information about the rock ("Method of eliminating the influence of acoustic excitation on nuclear magnetic resonance data", RF application No. 2005138896, IPC G01V 3/32, publ. 2007.06.20), in which a nuclear magnetic logging tool is introduced into the drilled in the thickness of the rock borehole, receive the primary sequence of echo signals of nuclear magnetic resonance (NMR), carry out the evaluation of the magnitude of the signal, not associated with NMR and resulting from the auxiliary sequence of pulses, and carry out the correction of the echo signal in between primary sequence of NMR echo signals using a signal evaluation unrelated to NMR.

A device for nuclear magnetic logging (AS USSR No. 669898, IPC G01V 3/32, publ. 2000.04.20) containing a polarization current source, keys and a polarization coil with taps that are connected through the key contacts to the polarization current source and input measuring amplifier, switch.

A device for nuclear magnetic logging ("Calculation of the characteristics and selection of elements of the NMR equipment" B. Tetelbaum, All-Russian Research Institute of Nuclear. Geophys. And Geochemistry, M .: 1984, 12 pp.), Containing the main inductor, switch, amplifier, input stump.

The known device cannot be used for research in wells, the precession frequency of which varies over a wide range up to 400 Hz with a frequency gradient of 10 Hz per 10 m.

Inaccurate tuning to the precession frequency leads to large errors in determining the initial amplitude of the free precession signal during nuclear magnetic logging, and sometimes even excludes the possibility of signal separation against the background of interference.

Known interference-free method for complex measurements of nuclear magnetic properties of rocks in a well during logging ("Method for measuring the nuclear magnetic properties of rocks in a well", RF patent No. 2148843, IPC G01V 3/32, G01N 24/00, publ. 2000.05.10) , the closest in technical essence and the totality of coinciding features to the claimed method and adopted as a prototype, in which the surrounding rocks are polarized, the received signal is subjected to direct Fourier transform. After that, the nuclear induction signal is re-excited and its frequency is measured, the frequencies of the nuclear induction signals are compared, and the magnetic field induction in the well before and after polarization is judged by the ratio of frequencies in the first and third measurements. As a result of the Fourier transform, the original signal is converted from the temporal to the frequency representation, which makes it possible to apply digital filtering of the signal and measure the amplitude and width of the spectral line of the proton resonance.

However, in the known method, it is necessary to polarize the medium three times and conduct the Fourier transform three times, which increases the time of logging. With a polarization time of 2 s and a Fourier calculation duration of 0.8 s, the total time of one measurement cycle of the signal from the reservoir will be (2 + 0.8) * 3 = 8.4 s.

The known method is implemented by a device for measuring the nuclear magnetic properties of rocks in the well during logging, which is the closest but technical essence to the claimed device and is taken as a prototype. The device includes a downhole tool comprising an NMR sensor, a measurement, control, and tuning circuit associated with a polarization current pulse generator using a wireline cable, and a processor unit.

The processor unit is located on the surface, i.e. the processed signal is transmitted via cable to the surface in analog form. The geophysical cable inherently represents an additional source of all kinds of interference, which greatly distorts the shape of the transmitted useful signal, which, in turn, increases the likelihood of errors in determining the initial amplitude of the signal.In addition, the control of tuning the NMC sensor to the resonant frequency occurs from the surface, which also takes time and complicates the control and configuration scheme. The tuning range for the signal precession frequency in such a device is limited to a band of 128 Hz, which does not overlap with the anomalous change in the precession frequency in real wells currently being drilled.

The range of changes in the precession frequency in the study interval in some of them reaches 400 Hz. In such wells, with large detuning values, registration of the useful signal from the reservoirs may become impossible or the initial amplitude of the received signal will be determined with a large error.

The technical result to which the invention is directed is to increase the accuracy of registration of nuclear magnetic logging signals, the precession frequency of which varies widely up to 400 Hz with a frequency gradient of 10 Hz by 10 m, reducing the logging time and reducing the level of interference.

The technical result is achieved by the fact that in the method of nuclear magnetic logging, which includes polarization by a constant magnetic field of the rocks surrounding the well, subsequent measurement of the nuclear magnetic induction signal from the formation with the magnetic field turned off, the Fourier transform of the measured nuclear magnetic induction signal, new is that determination of the resonant frequency of the nuclear magnetic induction signal and subsequent tuning to this frequency is carried out in one polarization-measurement cycle, and tuning to the resonant frequency Nuclear magnetic induction signal occurs after each polarization.

Tuning to the resonant frequency is carried out in the range up to 400 Hz.

In a nuclear magnetic logging device comprising a downhole tool, consisting of an NMR sensor, a measurement, control, and tuning circuit associated with ground-based equipment consisting of a polarization current pulse generator and a measurement unit, using a wireline processor, a processor is new that the processor is located inside the downhole tool and is connected to the NMR sensor and the measurement, control and tuning circuit, and additional capacitors are introduced into the measuring, control and tuning circuit with the possibility of their connection to emya NMR probe tuning the resonance frequency.

The essence of the method is as follows.

First, the surrounding layers are polarized in the well. After the polarization is completed, a nuclear magnetic induction signal is received from the formation, which then undergoes a direct Fourier transform, then the resonant frequency of the nuclear magnetic induction signal is determined and the NMR sensor is tuned to this frequency, digitization of the nuclear magnetic induction signal and subsequent transmission of the received signal to the surface.

To determine the resonant frequency, a signal is not required but a cable to the surface, because the processor is located in the downhole tool and the cable does not introduce additional interference. This ensures the separation of the nuclear magnetic logging signal against the background of interference, i.e. its registration and increases the accuracy of determining the initial amplitude of the signal.

The proposed method allows tuning the NMR sensor to the precession frequency for one measurement cycle in the range of 400 Hz, and the determination of the resonant frequency of the signal occurs after each polarization cycle.

The proposed method is implemented in a nuclear magnetic logging device, shown in figure 1.

The nuclear magnetic logging device (Fig. 1) consists of a downhole tool 1, and ground equipment 2, which includes a polarization current pulse generator 3 and a measurement unit 4. The downhole tool 1 contains an NMK sensor 5, a processor 6, a measurement, control, and tuning circuit 7 and connected to ground equipment 2 using a wireline cable 8.

The measurement, control and tuning circuit 7 further comprises a set of capacitors with different tuning capacities, which provide tuning of the NMC sensor 5 to the resonant frequency of the signal from the formation.

The introduction of additional capacitors allows you to configure the NMK 5 sensor in the frequency range of 400 Hz.

The measurement of the resonant frequency occurs in the range from 0 to 4096 Hz. In the range of 400 Hz (relative to the average frequency of 2300 Hz), the NMR 5 sensor is tuned to the resonant frequency of the signal. This occurs due to a change in the measurement, control, and tuning circuit 5, namely, by adding additional capacitors to it.

Adding additional capacitors to the measurement, control and tuning circuit 5 allows you to expand the tuning and tuning range to 400 Hz.

The device operates as follows.

The polarization current pulses from the polarization current pulse generator 3 are fed into the downhole tool 1 to the NMK sensor 5, i.e. polarization of the environment in the well is performed. After polarization is completed, the NMK sensor 5 registers a nuclear magnetic induction signal, which arrives at processor 6 and in parallel to the measurement, control, and tuning circuit 7. In processor 6, the resonant frequency of the signal is determined and, processor 6 sends a command to the measurement, control, and tuning circuit 7 where the required number of capacitors is connected, which allows you to configure the NMK 5 sensor to the resonant frequency of the signal from the reservoir. Next, the reception, digitization and amplification of the nuclear magnetic induction signal takes place, which is digitally transmitted via cable 8 to the ground equipment 2 to measurement unit 4, where the visualization and final processing of the nuclear magnetic induction signal takes place. 11After the signal is transmitted to the surface, the polarization and measurement cycle is repeated.

In each cycle of measuring the NMR sensor 5 of the nuclear magnetic induction signal from the formation, the resonant frequency of the signal from the formation is determined using processor 6, and by connecting the required number of capacitors in the measurement, control and tuning circuit, the NMR sensor 5 is tuned to this frequency.

The processor 6 controls the measurement, control and tuning circuit 7 to fine tune the NMR sensor 5 to the precession frequency, i.e. in resonance with the received signal. This ensures an increase in the accuracy of recording signals from formations in wells, the precession frequency of which varies over a wide range up to 400 Hz with a sharp gradient of frequency change of more than 10 Hz per 10 m.

To determine the resonant frequency, it is not necessary to transmit a signal through the logging cable 8 to the surface, since the processor 6 is located in the downhole tool 1 and the logging cable 8 does not introduce additional interference. This ensures the separation of the nuclear magnetic logging signal against the background of interference, i.e. its registration and increases the accuracy of determining the initial amplitude of the signal.

The inventive method of nuclear magnetic logging and a device for its implementation allow tuning to the precession frequency for one measurement cycle in the range of 400 Hz, and the determination of the resonant frequency occurs before the start of measurement in each cycle.

The inventive method of nuclear magnetic logging and a device for its implementation are implemented in the borehole equipment Yak8, developed by LLC "TNG-Group", Bugulma. The YaK8 equipment is used in the production units of the company when performing NMR studies in drilled wells, both on the territory of Tatarstan and beyond.

Claims (2)

1. A nuclear magnetic logging device comprising a downhole tool, consisting of a NMR sensor, a measurement, control and tuning circuit associated with ground-based equipment consisting of a polarization current pulse generator and a measurement unit, using a wireline cable, a processor, characterized in that the processor is located inside the downhole tool and is connected to the NMK sensor and the measurement, control and tuning circuit. 2. The device according to claim 1, characterized in that the NMR sensor is configured to tune to a resonant frequency in the range up to 400 Hz.