RU172839U1 - Device for conducting pulsed neutron gamma-ray logging - Google Patents

Abstract

Usage: for conducting pulsed neutron gamma-ray logging. The essence of the utility model lies in the fact that the device contains a pulsed fast neutron generator, two detection units in the form of scintillation gamma-ray detectors, a power supply unit that generates secondary supply voltages, a cable entry, a transceiver unit connected by a bi-directional bus to a transceiver automaton implemented in the form of a programmable logic integrated circuit module - FPGA, high voltage blocks, detection blocks, digital-to-analog converter block, two analog-to-c blocks digital conversion, connected to data processing units implemented as a programmable logic integrated circuit (FPGA) module; the FPGA includes a synchronization block that provides control pulses for a pulsed fast neutron generator and data processing blocks, while the analog-to-digital conversion blocks contain analog-to-code converters characterized by a high clock frequency, the outputs of which are connected to the inputs of the data processing units. Effect: providing the possibility of reducing the measurement error. 1 s.p. f-ly, 3 ill.

Description

The utility model relates to nuclear geophysics and is designed 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.

The well-known "Method of pulsed neutron logging and a device for its implementation" (US Pat. RF No. 2262124, G01V 5/40, priority 05/26/2004, published 10/10/2005), in which for recording GINR (gamma radiation of inelastic scattering) and GIRZ ( gamma radiation radiation capture) uses a design scheme with a single probe.

The disadvantages of the known device include the underestimation of the borehole component of the measured characteristics of the section, since measurements with a single probe include both reservoir and 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 reservoir and borehole components (distant) (Pulse neutron gamma-ray spectrometric logging AINC - 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 a transceiver automaton, implemented as a programmable logical integral module with circuits (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 a FPGA module and processing blocks data.

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 amplitude-time spectra of gamma radiation from the reservoir component of the section.

In the known equipment, there is a distortion 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 studied section, but there is a measurement error due to the superposition on the measurements of the far probe (reservoir component) downhole component measurements.

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

This problem is solved by the fact that in the claimed 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 photoelectronic multiplier, a screen for protecting one of these detectors from direct pulse radiation a fast neutron generator, a power supply unit generating secondary supply voltages, a cable entry, a transceiver unit connected by a bi-directional bus to av tomato transceiver, implemented in the form of a programmable logic integrated circuit (FPGA) module, high voltage units, providing power to the respective detection units, digital-to-analog converter unit, generating control signals for high-voltage units, two analog-to-digital conversion units, connected to data processing units implemented as an FPGA module, in contrast to the known, a synchronization block is introduced into the programmable logic integrated circuit (FPGA), bespechivaet control pulses for the pulse generator of fast neutrons and the data processing blocks, wherein the blocks of digital-analog converters comprise transformations "analog code" that operate at high clock frequency in synchronism with the data blocks. In addition, an information storage unit representing non-volatile memory is introduced into the device circuit.

In FIG. 1 shows a pulsed neutron gamma ray device.

In FIG. Figure 2 shows an example of a signal digitized by an ADC unit.

In FIG. 3 shows an example of the temporal distribution of a signal.

A device for conducting pulsed neutron gamma-ray logging comprises a controlled fast neutron generator 1, two detection units 2 and 3, located at different distances from the fast neutron generator and consisting of gamma-ray scintillation detectors optically connected to a photoelectron multiplier, a screen (in FIG. not shown), 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 the unit m of the transmitter-receiver 6, which is connected by a bi-directional bus 7 with an automatic machine of the transceiver 8, implemented as 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 corresponding detection units 2 and 3 , a digital-to-analog converter unit 12, generating control signals for high voltage units 10 and 11, two analog-to-digital conversion units 13 and 14 connected to respective data processing units 15 and 16, implemented as FPGA module, the inputs of the analog-to-digital conversion blocks 13 and 14 are connected to the corresponding detection blocks 2 and 3, as well as the synchronization block 17 included in the FPGA, which provides control pulses for the fast neutron generator 1 and data processing blocks 15 and 16, and the microprocessor 18, which is part of the FPGA, that controls the fast neutron generator 1 and the blocks 15 and 16, 17, 8 connected to it by bidirectional buses 19, 20, 21, 22, 23 through connection 25, the information storage unit 24, connected to the microprocessor rum 18, while the blocks of analog-to-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 - connection bus between digital-to-analog converter unit 12 and microprocessor 18 (Fig. one).

In the claimed utility model, the parameters necessary for the standard complex of nuclear-physical methods (NFM) are measured in a two-probe modification (“Methodological recommendations for the use of nuclear-physical well logging methods (geophysical well surveys), including carbon-oxygen logging, to estimate oil and gas saturation reservoir rocks 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 a 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 separate 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), measurements are taken 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, a 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.

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 — the microprocessor ROM 18 — starts to run. As a result of the program, the necessary settings for the transceiver unit 6 and the digital-to-analog converter unit are set. 12 and the blocks of analog-to-digital converters 13 and 14. The block of the digital-to-analog converter 12, after the initial initialization, establishes the control their levels at the inputs of high-voltage blocks 10 and 11, which then supply high-voltage power to the detection blocks 2 and 3. Also, at the beginning of the program, the microprocessor 18 sets the necessary parameters of the transceiver block 6, the transceiver automaton 8, and the data processing blocks 15 and 16 and synchronization unit 17.

Further operation of the device is determined by control commands from the surface. The 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 input of the transceiver machine 8, decoded and transmitted to microprocessor 18. Microprocessor 18 analyzes the command and, if necessary, sets the parameters of the high voltage 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 synchronization unit 17 generates control pulses, and the microprocessor 18 receives information about its state from the neutron generator 1 through the 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 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.

In FIG. 2 shows a view of the digitized signals.

It can be seen from the figure that the width of the recorded signal is less than 200 ns, which can significantly reduce miscalculations.

In FIG. Figure 3 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 (2)

1. 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 photoelectronic multiplier, a screen for protecting one of these detectors 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 to a transceiver automaton implemented in ide module of a programmable logic integrated circuit - FPGA, high voltage units providing power to the respective detection units, digital-to-analog converter unit generating control signals for high voltage units, two analog-to-digital conversion units connected to data processing units implemented as a module programmable logic integrated circuit - FPGA, characterized in that a synchronization block is introduced into the FPGA, which provides control pulses for the pulse th fast neutron generator and data processing units, wherein the blocks are an analog-digital conversions contain characterized by a high clock frequency converters "analog code", the outputs of which are connected to the data inputs of the processing units. 2. A device for conducting pulsed neutron gamma-ray logging according to claim 1, characterized in that an information storage unit representing a non-volatile memory is introduced into the device circuit.

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