RU2650794C1 - Method and device for carrying out of the pulse neutron gamma logging (options) - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: usage for carrying out of the pulsed neutron gamma-ray logging. Summary of the Invention is in the fact that they carry out periodic irradiation of borehole space and rocks with the pulses of the fast neutron generator, registration of inelastic gamma rays (gamma quanta) scattering (IGRS) of fast neutrons, capture gamma rays (CGR) of thermal neutrons and temporal distributions of gamma radiation from radiation capture in pauses between the generator pulses in real time with continuous movement of the downhole tool and at the given quantization step, accumulation and registration within the given time cycle of the full amplitude-time spectra of fast neutron IGRS and thermal neutron IGRS, the periodic irradiation of the downhole and rocks with pulses of the fast neutron generator is performed at the operating frequency of the generator that is selected from the range of 1,000–400 Hz, and measurement of temporal distributions of gamma quanta is performed in pauses between the pulses, which are set within the range of 2,500–1,000 mcs. Two options of the device for implementing the claimed method are proposed.

EFFECT: ensuring the possibility of reducing the measurement error due to the increased accuracy of the separation of the borehole and reservoir components of the investigated section.

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Description

The group of inventions relates to nuclear geophysics and is intended to perform well research in order to determine the current oil saturation and to clarify the lithological and reservoir characteristics of reservoir layers crossed by a well.

In known devices for pulsed spectrometric neutron logging with a single probe (Method of pulsed neutron logging and device for its implementation. Pat. RF №2262124, G01V 5/40, priority 05/26/2004, published 10/10/2005) uses a generator frequency of 10-20 kHz with a generator pulse width of 15-25 μs, which causes the superposition of the SINR (gamma radiation of inelastic scattering) and the SIRS (gamma radiation of radiation capture) from previous generator pulses to the recorded SINR and the need for subsequent cleaning of the spectrum from overlapping radiation was.

Also, in the known device, the temporal distribution of gamma rays of GIRZ is recorded in order to determine the average lifetime of thermal neutrons. Measurement of the distribution of gamma rays over time is implemented in the pauses between the series of pulses of the generator. The length of such a pause is 2000 μs and is comparable with the lifetime of thermal neutrons in the medium under study, and there are overlapping responses from a series of pulses to measurements in a pause, which significantly distorts the nature of the temporal distribution of gamma rays, which affects the results of logging.

The disadvantages of this method include the underestimation of the borehole component of the measured characteristics of the section, since measurements with one probe include both the reservoir and the borehole components.

Known devices for pulsed spectrometric neutron logging, performing registration at two distances from the neutron generator (two probes), one of which characterizes the borehole component of the section (near), and the second - the reservoir and borehole components (distant) (Pulse neutron gamma-ray spectrometric logging device AINC -73С-2. Www.vniia.ru/ng/apkarotazh.html).

These devices also use a generator frequency of 10–20 kHz with a pulse width of the generator 15–25 μs, and registration of time distributions of gamma rays is also performed in the pauses between series (trains) of pulses. Due to the high frequency of the generator, these devices are also not free from superimposing energy spectra on top of each other, and the method of recording time distributions does not allow to completely separate the borehole and reservoir components of the studied section even when using measurements on two different probes. This is due to the fact that measurements at the near probe characterize the borehole component, while measurements at the far probe are deeper, but not free from the contribution of the borehole component, as a result, the error accumulates during measurements, which reduces the accuracy of determining the studied characteristics of reservoirs crossed by the well.

As a prototype of the claimed device adopted pulsed neutron gamma-ray spectrometric logging AINK-73C-2. www.vniia.ru/ng/apkarotazh.html.

The known equipment is dual-probe and contains a pulsed fast neutron generator, two scintillation gamma-ray detectors optically connected to a photoelectronic multiplier, a screen for protecting the scintillation detector from direct radiation from a pulsed fast neutron generator, a power supply unit that generates secondary supply voltages, a cable input, a transceiver unit, connected by a bi-directional bus with an automatic transceiver, implemented as a programmable logic integrated circuit module we (FPGA), blocks the high voltage to ensure power corresponding to the detection blocks, the block-analog converter, which forms control signals for the high voltage block, two blocks of the analog to digital conversion connected to the data processing unit, implemented as a module FPGA and data processing units.

Known equipment provides pulsed neutron gamma-ray logging, which includes periodic irradiation of the borehole space and rocks with pulses of a fast neutron generator, registration of gamma radiation of inelastic scattering (GINR) of fast neutrons, gamma radiation of radiation capture (GIRZ) of thermal neutrons and time distributions of GIRZ in pauses between pulses of the generator in real time with continuous movement of the downhole tool and a given quantization step, the accumulation in Within a given step of the full amplitude-time spectra of the fast neutron GINR and thermal neutron scattering spectra in the entire energy range by two gamma radiation detectors located in the downhole tool at such distances that one of them (near) records the amplitude-time spectra of gamma radiation from the borehole component of the well section, and the second - the amplitude-time spectra of gamma radiation from the reservoir component of the section.

In the known equipment, as mentioned earlier, there are distortions of both energy and time spectra, despite the use of two probes, which provides the primary separation of the borehole and reservoir components of the investigated section, but there is a measurement error due to the superposition of the far probe (reservoir component) measurements of the downhole component.

The problem that the claimed group of inventions solves is to reduce the measurement error due to the increased accuracy of separation of the borehole and reservoir components of the studied section.

The problem is solved by using the frequency of the neutron generator, at which the superposition of the spectra is minimal for the given specific measurement conditions associated with the characteristics of the well section, probe length, etc. This frequency is in the range of 1000-400 Hz, which was chosen experimentally.

The specified problem in terms of the method is solved by the fact that in the claimed method for conducting pulsed neutron gamma-ray logging, including periodic irradiation of the borehole space and rocks with pulses of a fast neutron generator, registration of gamma radiation (gamma quanta) of inelastic scattering (GINR) of fast neutrons, gamma radiation radiation capture (GIRZ) of thermal neutrons and time distributions of gamma radiation radiation capture in the pauses between pulses of the generator in real time with continuous the movement of the downhole tool and the specified quantization step, the accumulation and registration within the specified time cycle of the full amplitude-time spectra of gamma radiation of inelastic scattering of fast neutrons and gamma radiation of thermal neutron capture in the entire energy range, in contrast to the known periodic irradiation of the borehole space and rocks by pulses of a fast neutron generator produce at the operating frequency of the generator selected from the range of 1000-400 Hz, and the registration of temporary gamma-quantum distributions are carried out in pauses between pulses set in the range of 2500-1000 μs.

The specified task in terms of the device according to the first embodiment is solved by the fact that in the inventive device for conducting pulsed neutron gamma-ray logging containing a pulsed fast neutron generator, two detection units in the form of scintillation gamma-ray detectors optically connected to a photoelectron multiplier, a protection screen of one of these detectors from direct radiation of a pulsed fast neutron generator, a power supply unit forming secondary supply voltages, a cable entry, a transceiver unit, with a single bidirectional bus with an automatic transceiver, implemented as a programmable logic integrated circuit (FPGA) module, high voltage units that supply power to the respective detection units, a digital-to-analog converter unit that generates control signals for high-voltage units, two analog-to-digital conversion units connected to data processing units implemented in the form of a FPGA module, in contrast to the well-known programmable logical integrated circuit In addition, a synchronization unit was introduced that provides control pulses for a pulsed fast neutron generator and data processing units, while the analog-to-digital conversion units contain analog-to-code converters operating at a high clock frequency synchronously with the data processing units. In addition, an information storage unit representing non-volatile memory is introduced into the device circuit.

This problem in terms of the device according to the second embodiment is solved by the fact that in the inventive device for conducting pulsed neutron gamma-ray logging containing a pulsed fast neutron generator, a detection unit in the form of a scintillation gamma-ray detector optically connected to a photoelectronic multiplier, the screen protects the detector from direct radiation of a pulsed fast neutron generator, a power supply unit generating secondary supply voltages, cable entry, a transceiver unit connected to a bi-directional bus with an automatic transceiver, implemented as a programmable logic integrated circuit (FPGA) module, a high voltage unit that provides power to the detection unit, a digital-to-analog converter unit that generates control signals for the high-voltage unit, an analog-to-digital conversion unit connected to the data processing unit implemented in the form of FPGA module, in contrast to the well-known in the programmable logic integrated circuit (FPGA), a synchronization block is introduced, providing control pulses for a pulsed fast neutron generator and a data processing unit, while the analog-to-digital conversion unit contains an “analog-to-code” converter operating at a high clock frequency synchronously with the data processing unit. In addition, an information storage unit representing non-volatile memory is introduced into the device circuit.

In FIG. 1 shows a device for pulsed neutron gamma-ray logging according to the first embodiment.

In FIG. 2 shows a pulsed neutron gamma-ray logging device according to the second embodiment.

In FIG. Figure 3 shows an example of a signal digitized by an ADC unit.

In FIG. 4 shows an example of the temporal distribution of a signal.

The device according to the first embodiment contains a controlled fast neutron generator 1, two detection units 2 and 3, located at different distances from the fast neutron generator and consisting of scintillation gamma-ray detectors optically connected to a photoelectron multiplier, a screen (not shown in Fig.), located between the fast neutron generator 1 and the detection unit 2 closest to it, a power supply unit 4 forming secondary supply voltages connected by a cable entry 5 to a transceiver unit 6, which is connected inen bidirectional bus 7 with automatic transceiver 8, implemented in the form of a programmable logic integrated circuit (FPGA) module 9, two high voltage units 10 and 11, the outputs of which are connected to the inputs of the respective detection units 2 and 3, the digital-to-analog converter unit 12, which generates control signals for high voltage blocks 10 and 11, two analog-to-digital conversion blocks 13 and 14 connected to the corresponding data processing blocks 15 and 16, implemented as an FPGA module, and the inputs of the blocks are the ogo-digital conversion 13 and 14 are connected to the corresponding detection units 2 and 3, as well as the synchronization unit 17 included in the FPGA, providing control pulses for the fast neutron generator 1 and data processing units 15 and 16, and the microprocessor 18 included in the FPGA, performing general control of the fast neutron generator 1 and blocks 15 and 16, 17, 8, connected with it by bidirectional buses 19, 20, 21, 22, 23 through connection 25, the information storage unit 24, connected to the microprocessor 18, while the blocks are similar digital converters 13 and 14 contain analog-to-code converters operating at a high clock frequency synchronously with data processing units 15 and 16. Standard buses - positions: LVDS - parallel differential bus, АМВ АХ14 - common FPGA bus, SDIO - bus between microprocessor 18 and information storage unit 24, SPI is the connection bus between the digital-to-analog converter unit 12 and microprocessor 18 (Fig. one).

The device according to the second embodiment comprises a controllable fast neutron generator 1, a detection unit 2, consisting of a scintillation gamma-ray detector optically connected to a photoelectronic multiplier, a screen (not shown in FIG.) Located between the fast neutron generator 1 and detection unit 2, block power supply 4, which forms secondary supply voltages, connected by a cable entry 5 with a transceiver unit 6, which is connected by a bi-directional bus 7 with an automatic transceiver 8, implemented as a module programmable logic integrated circuit (FPGA) 9, a high voltage unit 10, the output of which is connected to the input of the detection unit 2, a digital-to-analog converter unit 12, which generates control signals for the high-voltage unit 10, an analog-to-digital conversion unit 13 connected to the data processing unit 15 implemented in the form of a FPGA module, wherein the input of the analog-to-digital conversion unit 13 is connected to the detection unit 2, as well as the synchronization unit 17 included in the FPGA, which provides control pulses for I of the fast neutron generator 1 and the data processing unit 15, and the microprocessor 18 that is part of the FPGA, which controls the fast neutron generator 1 and the blocks 15, 17, 8 connected to it by bidirectional buses 19, 20, 22, 23, the information storage unit 24 connected to the microprocessor 18, while the analog-to-digital conversion unit 13 contains analog-to-code converters operating at a high clock frequency synchronously with the data processing unit 15 (Fig. 2).

The claimed invention implements the measurement of the parameters necessary for a standard complex of nuclear-physical methods (NPS) in a two-probe modification ("Methodological recommendations for the use of nuclear-physical well logging methods (geophysical studies of wells), including carbon-oxygen logging, to assess the oil and gas saturation of rocks -collectors in cased wells "/ Edited by V.I. Petersilier, GG Yatsenko. - Moscow-Tver: VNIGNI, Scientific and Production Center" Tvergeofizika ", 2006).

To irradiate rocks with neutrons, a controlled fast neutron generator operating in a pulsed mode is used. A neutron generator emits neutrons with an energy of 14 MeV. The device registers secondary gamma radiation generated during inelastic scattering (GINR) and radiation capture (GIRZ) reactions with its separation by energy and time. Inelastic scattering is a threshold reaction with a characteristic threshold value of the neutron energy and the characteristic energy of the generated gamma quantum for each probable reaction. GINR occurs in a short time interval after the neutron leaves the target of the generator, which is determined by the time of neutron deceleration to threshold reaction values. In the majority of sections composed of sedimentary rocks, this time does not exceed units of microseconds, so the GINR is localized in time in the interval of the generator radiation. When fast neutrons are slowed down to thermal energies, the main reaction becomes radiation capture, generating gamma-ray lines characteristic of each element. The process of propagation of thermal neutrons in a medium is diffusive, the duration of this process depends on the composition and density of the substance and is characterized by the average lifetime of thermal neutrons, which for sedimentary rocks varies in the range from hundreds to thousands or more microseconds. Thus, it is possible to divide the time intervals with the maximum contributions of the GINR and GIRZ. An analysis of the recorded energy distributions (spectra) of the GINR and GIRZ makes it possible to assess the content of elements whose characteristic lines are presented in these spectra and, ultimately, the oil saturation of reservoir layers. The distribution of gamma rays over time contains information on the average lifetime of thermal neutrons, which is a generalizing characteristic of the medium as a whole and is widely used in the interpretation of NFM data to determine the gas saturation of reservoir layers.

In the proposed device, which has two probes (Fig. 1) or one probe (Fig. 2), measurements are carried out at a generator frequency in the range of 1000-400 Hz and time distributions are measured in the pauses between pulses of the order of 1000-2500 μs, which are quite comparable with the lifetime of thermal neutrons in the medium under study, and these measurements are free from the contribution of responses from neutron momenta. Moreover, the superposition of energy spectra is practically absent. In this regard, this device implements a reliable separation of the borehole and reservoir components of the studied section of the well. To implement such measurements, continuous digitization of the analog signal at high speed and a special signal processing algorithm are used to ensure high throughput of the spectrometric path. Measurements are performed with a small number of miscalculations and low statistical error at high loads.

In order to more fully disclose the implementation of the method, the operation of the device with two probes is presented (Fig. 1).

When a supply voltage is applied to the cable entry 5, the power supply unit 4 starts to work and forms secondary voltage levels necessary for electronic circuits. The controlled fast neutron generator 1 is powered directly from the cable input 5. When the supply voltage appears, the program located in the read-only memory of the microprocessor 18 starts to run. As a result of the program, the necessary settings for the transceiver unit 6, the digital-to-analog converter unit 12, and the analog-to-digital converter units 13 and 14. The block of the digital-to-analog converter 12 after the initial initialization carries out the establishment of control levels it at the inputs of the high voltage blocks 10 and 11, which then supply high voltage to the detection blocks 2 and 3. Also at the beginning of the program microprocessor 18 sets the necessary parameters of the transceiver unit 6, the automatic transceiver 8, data processing units 15 and 16 and the synchronization unit 17.

Further operation of the device is determined by control commands from the surface. Commands encoded in the Manchester-2 code, through cable input 5, are input to the transceiver unit 6, converted to a digital code and then fed to the transceiver machine 8, decoded and transmitted to microprocessor 18. Microprocessor 18 analyzes the command and, if necessary , sets the high voltage parameters on the block of the digital-to-analog converter 12, the parameters of the data processing units 15 and 16.

When power is applied, preparation of the neutron generator 1 for operation in the radiation mode begins, for this the synronization unit 17 generates control pulses, and the microprocessor 18 receives information about its state from the neutron generator 1 via bus 23. The radiation mode of the neutron generator is also activated by command from the surface. The frequency and duration of the neutron pulses is set by the synchronization unit 17 and is controlled by the microprocessor 18. In this case, the operating frequency of the neutron generator 1 is set from the range of 1000-400 Hz, and the time distribution of gamma rays is measured in the pauses between pulses set in the range of 2500-1000 μs.

Gamma quanta are detected by detection units 2 and 3, in the scintillators of which a light flash occurs, the number of photons of which is proportional to the energy of the gamma quantum lost in the detector and which is then converted into an electrical pulse in a photoelectronic multiplier. An electric pulse corresponding to the registered particle is fed to the input of the corresponding block of the analog-to-digital converter 13 and 14 and, after digitization using the parallel differential bus of the LVDS standard, to the input of the data processing blocks 15 and 16. The data processing units measure the pulse amplitude taking into account sampling errors in time, as well as reject superimposed pulses and form the amplitude and time spectra. The blocks of analog-to-digital converters 13 and 14 contain analog-to-code converters operating at a high clock frequency synchronously with the data processing units 15 and 16, which ensures continuous digitization without missing fast output pulses and their transmission to processing units 15 and 16. Thus Thus, the fast neutron generator 1 is controlled by the synchronization unit 17, and the blocks of analog-to-digital converters 13 and 14 provide continuous high-speed digitization of the input signal with subsequent synchronous processing in the processing units data 15 and 16 connected to the synchronization unit 17, which allows to reduce the width of the recording pulses, the probability of their overlap. As a result, the statistical error in the measurement is reduced.

The operation of the device with one probe is carried out similarly to the operation of the device with two probes, but a circuit is used that contains one data processing unit 15, one analog-to-digital converter unit 13, one detection unit 1, one high voltage unit 10 (Fig. 2).

In FIG. 3 shows a view of the digitized signals.

From the FIG. Figure 3 shows that the width of the recorded signal is less than 200 ns, which can significantly reduce miscalculations.

In FIG. Figure 4 shows the temporal distribution of the signal obtained simultaneously at two detection units at different distances from the generator at a frequency of 400 Hz in the model of a porous reservoir.

It can be seen that the count of the spectrometric path rapidly decreases over a time interval of up to 1 ms, while the GIRD from the previous flash does not contribute to the current measurement.

Claims (4)

1. The method of conducting pulsed neutron gamma-ray logging, including periodic irradiation of the borehole space and rocks with pulses of a fast neutron generator, registration of gamma radiation of inelastic scattering of fast neutrons, gamma radiation of thermal neutron capture and gamma radiation distribution of radiation capture in pauses between pulses of the generator in real time with continuous movement of the downhole tool and the specified quantization step, accumulation and registration in within a given time cycle of the full amplitude-time spectra of gamma radiation of inelastic neutron scattering and gamma radiation of thermal neutron capture in the entire energy range, characterized in that the periodic irradiation of the borehole space and rocks with pulses of a fast neutron generator is performed at the operating frequency of the generator selected from the range of 1000-400 Hz, and the registration of the full amplitude-time spectra of gamma radiation of inelastic scattering of fast neutrons and gamma radiation is glad thermal capture of neutrons is carried out in the pauses between pulses, set in the range of 2500-1000 μs. 2. A device for conducting pulsed neutron gamma-ray logging according to the first embodiment, comprising a pulsed fast neutron generator, two detection units in the form of scintillation gamma-ray detectors optically connected to a photoelectronic multiplier, a screen for protecting one of these detectors from direct radiation from a pulsed fast neutron generator , a power supply unit generating secondary supply voltages, cable entry, a transceiver unit connected by a bi-directional bus to an automatic transceiver implemented in the form of a programmable logic integrated circuit module - FPGA, high voltage blocks providing power to the corresponding detection blocks, a digital-to-analog converter block generating control signals for high voltage blocks, two analog-to-digital conversion blocks connected to data processing blocks implemented as module programmable logic integrated circuit - FPGA, characterized in that the FPGA has a synchronization unit that provides control pulses for a pulsed fast neutron generator and data processing units, while the analog-to-digital conversion units contain high-frequency analog-to-code converters whose outputs are connected to the inputs of the data processing units. 3. A device for conducting pulsed neutron gamma-ray logging according to the second embodiment, comprising a pulsed fast neutron generator, a detection unit in the form of a scintillation gamma-ray detector optically connected to a photoelectronic multiplier, a screen for protecting the detector from direct radiation from a pulsed fast neutron generator, a power supply, forming secondary supply voltages, cable entry, transceiver unit connected by a bi-directional bus with a transceiver automaton implemented in the form of m a programmable logic integrated circuit (FPGA) module, a high-voltage block providing power to the detection block, a digital-to-analog converter block generating control signals for the high-voltage block, an analog-to-digital conversion block connected to a data processing unit implemented as a FPGA module, characterized in that that a synchronization block is introduced into the FPGA, which provides control pulses for a pulsed fast neutron generator and a data processing unit, while the analog- The digital conversion characterized by comprising a high clock frequency converter "analog code", the output of which is connected to the input of the data processing unit. 4. A device for conducting pulsed neutron gamma-ray logging according to claim 2 and 3, characterized in that an information storage unit representing a non-volatile memory is introduced into the device circuit.

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