RU2073895C1 - Neutron activation logging method and device for it performing - Google Patents

Abstract

FIELD: geophysical prospecting engineering. SUBSTANCE: rock cyclic-discret neutron radiation flow exposing is making by well instrument moving from opening to bottom, induced gamma ray radiation appears correspondingly to well instrument moving velocity. Radiation flow N1 is measuring by gamma-quantum detector within interval length 40-60 cm and concentration of element is determining by induced gamma ray flow spectrum intensity measuring. Exposure is making by 14 MeV neutron flow puls generator and gamma ray induced radiation flow spectrum from nitrogen isotopic element 16 N2 is measuring additionally as function of time t with one step period 1-5 s by second gamma ray detector using which is placed by 40-60 cm upper than neutron source is placed and it is moving synchronously with the first one. Molecules N2 flow as function f(t) is measuring in interval between fast neutrons pulses with initial time delay t equal to 5-6 mcs when total cyclic exposure in one cycle is t=h/V where h is basic length of free displacement of neutron detector, V is well instrument raising up velocity. Spectrum intensity of N16 isotopic nuclear flow and it's raising time measuring permits seam overcurrent velocity of fluid and it relative intensity determining by V_f=l/t_f expression using where l is distance between second detector of gamma quantum and neutron pulse generator, t_f is time counting from exposure beginning moment of N2 flow entering to second detector area. Device for this method realizing has movable part of system control block and well instrument connected to surface control panel by geophysical cable. Surface control panel has depth pulse pick-up, n-capacity digital pulse counter, pulse amplitude analyzer, logging registrar, exposition block, power supply unit for well neutron generator and cycle start marker of exposure-metering beginning. Well instrument has additional second gamma quantum detector, second recorder-transmitting unit and moving part control block with depth signal pulses pick-up, end switch, blocking-up unit, second n-capacity digital pulse counter and second digit-analog converter. Moving system has second gamma ray quantum detector placed at 40-100 cm distance up with respect to neutron source position. EFFECT: higher accuracy of logging measurements. 2 cl, 3 dwg

Description

 The invention relates to applied nuclear geophysics and can be used for remote research of hard-to-reach objects by neutron activation in geology, mining, metallurgical or chemical production and other areas of the national economy.

A known method of neutron activation analysis of rocks, based on the irradiation of samples with a neutron flux and subsequent measurement of induced activity from indicator isotopes. The intensity of the induced gamma radiation determines the content of the element. A device that implements the method consists of an activation installation containing a neutron source and protective shields, pneumatic mail and analyzing equipment, including a detection unit and a pulse analyzer [1]
These method and device provide a highly sensitive determination of the content of elements, but only in samples. The application of the method and device for determining the elements, for example, in wells is impossible, since the studied medium is not samples, but rock masses.

 There is also known a method of radioactive logging, which consists in irradiating rocks with a neutron flux and measuring the induced effect of the indicator isotope during continuous movement of the downhole tool through the borehole at an optimal speed. For the practical implementation of the method, a device is proposed consisting of a downhole tool and ground-based measuring equipment. The downhole tool comprises a detecting unit, a fast neutron source, and a recording and transmitting circuit. The detection unit is located at a certain fixed distance from the neutron source and is protected from its direct radiation by screens. Ground-based measuring equipment is a 2-4-channel or multi-channel pulse analyzer connected to an analog or digital information recorder by output. As a neutron source in a downhole tool, controlled fast neutron generators can be used. In this case, the ground-based equipment includes a power unit for the downhole neutron generator [2]. The measurement results in the form of the count rate of the induced effect as a function of the depth of the well are recorded on a chart tape stretching synchronously with the rate of rise of the downhole tool. The presence of a determined element is noted in the form of anomalies, by the intensity of which they judge the occurrence boundaries of a certain type of mineral and the content of the analyzed element in the rocks.

 The main disadvantage of this method is its low sensitivity to the analyzed elements, which is due to the continuous mode of irradiation and measurement. In fact, the method allows to determine only the macro-content of elements whose isotopes have a short half-life (less than 5 min) and a high activation course.

 The closest in technical essence and the achieved result is the method of neutron activation logging, which consists in discrete irradiation of rocks with a neutron flux in the well during shutdown of the downhole tool and subsequent continuous recording of the induced effect in motion in the range of 20-40 cm, located symmetrically relative to the irradiation points [2] Known stationary sources or pulsed neutron sources are used as a neutron source during measurements new. To implement the method, a device is used that is absolutely identical to the above second analogue.

 Due to the discrete irradiation mode, the proposed technical solution allows increasing the sensitivity of neutron activation logs to the analyzed elements by 3-10 times, which, in particular, opens up the possibility of its use for solving geochemistry problems.

 The main disadvantage of this method is the low productivity and low-tech work. For example, to study the distribution of fluorine content in a well 300 meters deep with a step of 2 meters, 150 stops are required lasting 20-30 seconds. After each stop, it is necessary to dial the optimal speed of the downhole tool and register the irradiated point. It is easy to see that such a measurement technology in practice is very difficult to implement.

The present invention solves the problem of increasing the accuracy, productivity and manufacturability of neutron activation logging. To do this, according to the method of neutron activation logging, which consists in discrete irradiation of rocks with a neutron flux from a pulsed neutron generator and continuous registration of induced gamma radiation (N ₁ ) in the lengths of 20-40 cm, located symmetrically relative to the irradiated points, and the subsequent determination of the content of elements by the intensity of spectral flows recorded in characteristic regions of the energy spectrum, irradiation is carried out cyclically with continuous movement of the borehole device with optimal speed (V), for which, in each cycle, the neutron source is synchronously with the logging speed moved in the direction opposite to the movement of the downhole tool, at a distance from the gamma-ray detector equal to l ₁ t _p • V, then quickly return it to the initial the position at a distance from the gamma-ray detector, equal to l ₂ V (t _p + t _a ), where t _p and t _a are the calculated values of the pause and activation times, established from the conditions for recording the induced effect of the ith isotope with a minimum statistical error .

In addition, the spectral flux of the induced gamma radiation of the nitrogen-16 isotope (N ₂ ) is also measured as a function of time (t) with a quantization step of 1-5 sec using a second gamma detector located above the neutron source at a distance l of 40 -100 cm, and moving synchronously with it, and the flux N ₂ f (t) is measured between fast neutron pulses with an initial time delay after each pulse of t 5-6 ms for a total exposure of measurements in the th / V cycle, where h is the base of free movement neutron source and second det Ktorov gamma quanta on the rise time and the intensity of spectral flux from the nuclei of activated N-16 (N ₁₎ is determined isotope flow rate of formation fluid V _f l / t _f and its relative intensity Q _i, where l - distance between second gamma detector quanta and a pulsed neutron source, t _{f the} time of entry of the activated flux N ₂ into the region of the second detector, counted from the start of irradiation in each cycle.

 To implement the method, a neutron activation logging device is proposed, comprising a downhole tool with a ground control panel connected by a geophysical cable, the ground control panel comprising a pulse depth sensor, an amplitude pulse analyzer, a logging recorder and a fast neutron pulse source power supply, while the output of the pulse depth sensor is associated with logging recorder, the information input of which is connected to the output of the amplitude pulse analyzer, the first input connected to oh residential logging cable, a pulsed fast neutron source power supply output is connected to the third residential logging cable. The downhole tool consists of a security enclosure with a first gamma-ray detector placed in it, connected to the input of the first recording-transmitting circuit, at the output of the first living geophysical cable, with a pulsed fast neutron source separated from the first gamma-ray detector by a protective screen.

The proposed device differs from the known one in that the ground-based remote control additionally contains an n-bit pulse counter, a two-input exposure unit and a fixation circuit for the beginning of the irradiation-measurement cycle, the input of which is connected to the second core of the geophysical cable, and the output to the input is “zero” n -digit pulse counter and the second input of the exposure unit, the output of the pulse depth sensor is additionally connected to the second living geophysical cable and the information input of the n-bit pulse counter, the output connected to the first input of the exposure unit, the output of which is connected to the input input blocking "In.bl." an amplitude pulse analyzer equipped with a second information input, connected through a capacitance to the 3rd core of the geophysical cable. The downhole tool additionally contains a second gamma-ray detector, a second recording and transmitting circuit, a mobile system with a speed reducer and a micro-winch, a reversible electric motor, a control unit for the mobile system including a pulse depth sensor, a limit switch, a blocking circuit, the first and second n- bit pulse counters, n-bit digital comparator, n switches of logical levels of zero and one, the first and second digital-to-analog converters,
a comparison circuit and a zero-organ amplifier, wherein a second gamma-ray detector and a pulsed fast neutron source are placed in the mobile system, the gamma-ray detector being placed above the pulsed fast neutron source at a distance of 40-100 cm and connected via flexible communication (such as telephone) with the input of the second recording and transmitting circuit, the output connected to the 3rd core of the geophysical cable, the movable system is mechanically connected to the speed reducer, with a micro winch and a reversible electric motor, the output of the pulse sensor g Ubina is connected to the information input of the first n-bit pulse counter, and its output is connected by a bus to the input of the first digital-to-analog converter, the output of the second n-bit pulse counter is connected by a bus to the first input of the n-bit digital comparator and the input of the second digital-to-analog converter, n-bit output the digital comparator is connected to the inputs "zero" of the second n-bit pulse counter and the second digital-to-analog converter, the outputs of the first and second digital-to-analog converter lei are connected to the first and second inputs of the comparison circuit, the output associated with the input of the amplifier of the zero-organ,
connected at the output to a reversible electric motor, the outputs of the n logic level zero and one switches are connected via a bus to the second input of an n-bit digital comparator, the output of the limit switch is connected to the zero-setting input of the first n-bit pulse counter, the first digital-to-analog converter and the first control the input of the blocking circuit, the second control input of which is connected to the output of an n-bit digital comparator, the output of the blocking circuit is connected to the input of a second n-bit count pulse generator, and the input is connected to the second core of the geophysical cable.

 In FIG. 1 shows the dependences of the induced effect on oxygen nuclei measured by the second detector at two different inflow rates during the implementation of the proposed method.

The essence of the method consists, as in the prototype, in discrete irradiation of the medium by a fast neutron flux and registration of the induced gamma radiation by the first gamma detector during continuous movement of the downhole tool over an activated (irradiated) point and additional measurement of the spectral flux from the nitrogen-16 oxygen isotope by the second a gamma detector moving synchronously with a pulsed source of fast neutrons. Since the position of the latter is stabilized relative to the medium under study in each measurement cycle, the second detector can only detect gamma rays from naturally-occurring radioisotopes and isotopes that are carried out from the irradiation zone in the direction of the second gamma-detector, for example, due to the vertical flow of formation fluid through the well or annular space. Obviously, the intensity of the induced effect due to the removal of activated nuclei from the irradiation zone will depend on the flow rate, i.e. the intensity of the flow, and the time of entry of the front of activated nuclei into the region of the second gamma-ray detector determines the flow velocity at a fixed distance to the source of fast neutrons. It is advisable to use the nitrogen-16 oxygen isotope as an indicator isotope for determining the parameters of formation fluid flow (velocity, relative flow rate). The latter is formed by the reaction O ¹⁶ (n, p) N ¹⁶ with a threshold of 10 meV, has a short half-life (T 7.4 sec), and during decay emits intense hard radiation with energies of 6.4 and 7.1 meV. Due to the favorable activation characteristics, its radiation is easily distinguished with a discrimination level of 2.5-3 meV. The absence of other isotopes with such secondary radiation energy provides practically backgroundless measurements and, accordingly, a high sensitivity of the method to flows of formation and well fluid that always contains stable oxygen nuclei.

Since the second detector is located at a short distance from the fast neutron source (40-100 cm), and the O ¹⁶ (n, p) N ¹⁶ reaction proceeds at a neutron energy of more than 10 meV, a downhole fast neutron pulsed source (neutron generator) is required to activate the nuclei with an energy of more than 10 meV, for example, 14 meV. Measurement of the spectral flux from the N-16 isotope is easily achieved in the region of more than 2.5-3 meV with a time delay after each neutron pulse of t 5-6 ms. Such a time delay is necessary to eliminate background gamma radiation due to radiation capture of thermal neutrons by the nuclei of the medium under study and structural materials. At a neutron pulse repetition rate f of 20 Hz, the net measurement time of the induced effect from the N-16 isotope will be 44-46 ms.

At the same time, with the same initial time delay, the spectrum of natural and induced gamma radiation can be recorded. The activation and measurement time for the second gamma-ray detector is determined by the logging speed (V) and the base of free movement of the gamma-ray detector system is the neutron source (h). At h 180 cm, V 4 m / min t _a 1.8 / 4 m / min 0.45 min or 27 sec. This mode is close to optimal and allows one to determine the flow rates in the range from 40 to 3 cm / sec at l 40 cm and from 100 to 4 cm / sec at l 100 cm, where l is the distance between the gamma-ray detector and the pulsed fast neutron source. At lower flow rates, the estimation of its parameters decreases due to the decay of the N-16 isotope nuclei as the fluid moves from the activation zone to the region of the gamma-ray detector. So, with V _f 3 cm / sec, the activity is about 6% of the initial one.

Specifically, the flow rate can be determined from the curve of the front of activated nuclei of the N-16 isotope, for which the spectral intensity N ₂ in each cycle is measured as a function of time N ₂ f (t). An example of recording spectral intensity at two different flow rates V _f1 and V _f2 1/2 V _{f1 is} shown in figure 1. With an equal flow rate, the maximum effect is fixed at a flow velocity v $\genfrac{}{}{0ex}{}{\text{opt}}{\text{f}}$ = λ • l .. It follows from the formula that for l 100 cm and λ = 0.1 sec, v $\genfrac{}{}{0ex}{}{\text{opt}}{\text{f}}$ = 10cm / sec. At a speed of 0 to 10 cm / s, the induced effect increases, and at V _f > 10 cm / s it decreases again. However, this ambiguity affects only the determination of the relative rate and is easily eliminated by the time of arrival of the front of activated nuclei. In view of this, an estimate with respect to flow rate should be carried out using at least two dependencies for v _f <v $\genfrac{}{}{0ex}{}{\text{opt}}{\text{f}}$ and for v _f > v $\genfrac{}{}{0ex}{}{\text{opt}}{\text{f}}$ .
Since, ceteris paribus, the gamma-ray intensity recorded by the second detector in the saturation region (see Fig. 1) depends on the volume of the flowing liquid Q and its filtration rate, for the ith and reference (with known flow rate and flow rate) intervals, the relations
N _2i Q _i • V _i ;
N _fl Q _fl • V _fl
whence Q _i Q _floor • N _2i / N _2et • V _floor / V _i .

Actually, N ₂ activities are determined by the asymptotic branches of the N ₂ f (t) dependencies. Therefore, the registration of the stream N ₂ should be carried out as a function of time with a quantization step of 1-5 seconds. The time quantization interval is determined for reasons of ensuring sufficient accuracy for measuring the spectral fluxes N ₂ (t) and the time of entry of the front of the activated liquid into the detector region.

At the same time, the second gamma detector can be used to measure the full spectrum of natural and induced gamma radiation, which allows for the implementation of radio geochemical studies. The spectrum recorded by the proposed method contains information on the content in the rocks of naturally-radioactive elements (uranium, thorium, potassium) and the equivalent oxygen content in the activated liquid. Quantitative determination of all these elements is carried out in the usual way by solving a system of linear equations of the form
g (U) a ₁ N ₁ + b ₁ N ₂ + c ₁ N ₃ + d ₁ N ₄ ;
g (Th) a ₂ N ₁ + b ₂ N ₂ + c ₂ N ₃ + d ₂ N ₄ ;
g (K) a ₃ N ₁ + b ₃ N ₂ + c ₃ N ₃ + d ₃ N ₄ ;
g (O) d ₄ N ₄ ,
where g (U), g (Th), g (K) and g (O) are respectively the contents of uranium, thorium, potassium and oxygen; a _i , b _i , c _i , d _i spectral coefficients determining the contribution of the i-th isotope to the i-th energy region; N ₁ , N ₂ , N ₃ , N ₄ spectral intensities recorded in the region of the main gamma lines of uranium (1.78 meV), thorium (2.62 meV), potassium (1.46 meV) and oxygen (> 2, 5-3 meV).

In the absence of flows N ₄ 0, the system goes over into the usual system of equations, well known in spectrometric gamma-ray logging.

The first gamma-ray detector, which is located rigidly in the downhole tool, is used to register induced gamma radiation generated in rocks during its irradiation with a fast neutron flux in the same way as in the prototype. We only note that the use of a neutron generator as a source makes it possible to sharply increase the information content of the method due to the excitation of nuclei by threshold reactions: oxygen O ¹⁶ (n, p) N ¹⁶ , E _n 10 meV; sodium Na ²³ (n, p) Ne ²³ , E _n 3.5 meV and Na ²³ (n, α) F ²⁰ , E _n 4.5 meV; chlorine Cl ³⁷ (n, p) S ³⁷ , En _n 4.1 meV and Cl ³⁷ (n, α) P ³⁴ , En _n 1.44 meV and others. These isotopes are part of the reservoir fluid of oil-bearing formations and can be used for their identification, assessment of the nature of saturation, as well as quantitative determination of their reserves in the bowels.

 In ore deposits, the first gamma-ray detector can be used to detect such common and important elements as fluorine, aluminum and silicon. This information, combined with data on the content of naturally occurring radioactive elements, can be used to search for various endogenous deposits by scattering halos.

 For the practical implementation of the method of neutron activation logging, a device is proposed whose functional diagrams are shown in FIG. 2 and FIG. 3. Figure 2 presents the functional diagram of the downhole tool and ground console; figure 3 presents the functional diagram of the control unit of the mobile system.

 The following notation is used in the drawings: 1 gamma-ray detector, 2 first recording-transmitting circuit, 3 second gamma-ray detector, 4 second recording-transmitting circuit, 5 pulsed neutron generator, 6 mobile system, 7 protective screen, 8 reversible electric motor, 9 - speed reducer with a micro winch, 10 pulse depth gauge of a downhole tool, 11 device for laying a flexible communication line, 12 control unit for a mobile system, 13 transport cable, 14 flexible communication line of a second gamma-ray detector and source and neutrons, 15 n-bit pulse counter, 16 pulse depth sensor, 17 exposure block, 18 - scheme for fixing the beginning of the irradiation-measurement cycle, 19 logging recorder, 20 pulse analyzer, 21 power supply unit of a pulsed neutron generator, 22 blocking circuit, 23 limit switch, 24 and 25 first and second n-bit pulse counters, 26 n-bit digital comparator, 27 n switches of logical levels of zero and one, 28 and 29 - first and second digital-to-analog converters, 30 comparison circuit, 31 - zero amplifier -organ, R input "set and zero ", 1U and 2U first and second control inputs, and Inf.vh.1 Inf.vh.2 first and second data inputs, Vh.bl. blocking input.

 The device operates as follows. In the initial state, the mobile system 6 with a source of fast neutrons 5 and a second gamma-ray detector 3 is in its highest position. All counting elements are reset to zero. When moving up (to the right in the drawing), the pulse depth sensor 16 generates pulses, for example, one for each millimeter of movement of the downhole tool. These pulses are fed to the input of the n-bit pulse counter 15, the logging logger 19, and along the second core of the cable to the n-bit pulse counter 24 of the control unit of the mobile system 12, at the output of which the number of received pulses is displayed in binary code. On the n-bit bus, this code is supplied to the corresponding inputs of the digital-to-analog converter (DAC) 28 and the n-bit digital comparator 26. From the output of the DAC 28, the signal in analog form is supplied to the comparison circuit 30. Since its second input, a constant voltage is supplied from the output of the second DAC 29, which is in the reset state (the output has zero potential), an unbalance signal appears at the output of the comparison circuit 30, which, amplified by the amplifier by a null-organ 31, goes to the control input of the reversing electric motor 8 in the form of a voltage Nia, for example, positive polarity. The electric motor 8 begins to rotate until the pulse depth sensor of the downhole tool 10 is activated.

 The pulse from its output goes to the input of the second n-bit counter of pulses 15 of the control unit of the mobile system 12, the output of which the number of pulses is also reflected in binary code and through the n-bit bus goes to the input of the second DAC 29, which works identically with the first. As a result, the voltage at the inputs of the comparison circuit 30 becomes equal and the motor 8 is stopped. For synchronous movement of the mobile system 6 and the downhole tool, depth gauges 16 and 10 are used with the same quantization step of the pulse signals per unit of movement. As the downhole tool rises and 16 new pulses appear from the depth sensor 16, an unbalance signal appears again, which is similarly compensated by the electric motor 8 by means of a zero-organ amplifier 31. In this mode, the device operates until the mobile system 6 moves a distance ht • V, where t is the activation time, V is the logging speed. Suppose h is 1.8 meters. Then, at the moment the 1800th pulse arrives from the pulse depth sensor 16, a signal appears at the output of the n-bit digital comparator 26. Before working on the inputs of the second channel of the n-bit digital comparator, it is necessary to send a binary code of 1800 from n switches of logical levels of zero and unity 27. The signal from the output of the digital n-bit comparator prohibits the passage of pulses from the pulse sensor of depth 16 through the second core of the cable by closing the key blocking circuit 22, resets the n-bit counter of pulses 24 and DAC 28 to the initial zero state, which leads to a decrease at the first input of the comparison circuit 30 of the voltage to zero.

At the same time, at the second input of the comparison circuit, the voltage remains maximum. Accordingly, the unbalance signal is greatest and, most importantly, has the opposite polarity. As a result, the output of the amplifier of the zero-organ 31 also produces a signal, but of a negative polarity. The electric motor changes rotation, quickly moving the moving system with a fast neutron source 5 and a second gamma-ray detector 3 to its original state. At the time of the transition to the initial state, the limit switch 23 is activated, which resets the n-bit pulse counter 25 and the digital-to-analog converter 29 to zero and releases the input of the n-bit pulse counter 24 by opening the key of the circuit 22. At the time of release, a signal is generated in the circuit 22 , which in the form of a pulse, for example of negative polarity along the second core of the cable, is transmitted to the input of the fixation circuit of the beginning of the irradiation-measurement cycle 18. The output signal generated by this circuit resets the n-digit the second pulse counter 15 is in the zero state and goes to the second input of the exposure block 17, which controls the operation of the pulse analyzer 20. At the time of receipt of the signal 0, fixing the beginning of a new cycle "radiation-measurement", the 2nd information input of the pulse analyzer is released, and thus information is recorded from the second gamma-ray detector coming from the output of the second recording-transmitting circuit along the third core of the cable. In the same vein, a neutron generator (neutron source) is supplied with a constant voltage of 200-300 volts. The beginning of the registration of information from the first gamma-ray detector is realized upon the arrival of the 1800th pulse to the n-bit pulse counter 15. The measurement mode of induced gamma radiation N ₁ in a given research interval is set by the exposure unit 17 by blocking or releasing the first information input of the pulse analyzer. Information N ₁ to the input of the pulse analyzer 20 is transmitted from the first recording and transmitting circuit along the first core of the geophysical cable.

 Separate transmission of depth pulses from the pulse depth sensor 16 and the limit switch 23 along the second cable core is carried out by pulses of different polarity or different amplitudes. The power of the neutron generator 5 (source of fast neutrons) and the second gamma-ray detector 3 is carried out via a flexible communication line 14 of the type of telephone wire, self-compressing when stacked in the complete device 11. The speed reducer 9 serves to enhance the traction of the electric motor and ensure synchronous operation of the pulse depth sensor 10. The gearbox output is articulated with a micro winch for lifting the movable system 6 after the irradiation-measurement cycle. The synchronous descent of the system is effected by gravity and is facilitated by the use of plain bearings.

 Unlike the prototype in the proposed device, the synchronous movement of the movable system is controlled by pulses from two depth sensors, which eliminates the influence of changes in the ohmic resistance of the wires of the geophysical cable, leaks or changes in the reactance of the cable when working at different depths. This ensures more accurate stabilization of the source position at each point of the section and, accordingly, the accuracy of determining the contents of elements from spectral fluxes from indicator isotopes and parameters of the flow of formation or well fluid.

 The above functional diagram of a device for implementing the method is not unique. When using a geophysical cable of large length (more than 2-3 km), a pulse analyzer with an exposure unit is more appropriate to place directly in the downhole tool. In this case, the registration and transmission of information signals via cable can be carried out in digital form with its processing in a ground-based complex, including a microcomputer. The principle of operation of such a spectrometric system is described, for example, in the article Digital Downhole Spectrometer, Sat. Gamma spectrometry of wells in the search and exploration of oil and solid minerals, M. VNIIGeoinformsistem, 1987, p. 64-68.

The capabilities of the method were investigated experimentally on physical models using a breadboard model of a downhole tool with a 14-meV pulsed neutron generator, providing a neutron yield of 2 • 10 ⁷ n / s. To record the natural and induced gamma radiation, scintillation detectors of gamma quanta of the Nal (Tl) type with a size of 50x150 mm paired with a PMT-151 were used.

According to the results of the experiments, it was found:
the error in determining the flow rate depends on its flow rate and is less than 10% relative at a flow rate of more than 0.5 liters / sec,
the method provides a relative estimate of the production fluid flow rate in wells at a flow rate of from 3-4 cm / s to 80-100 cm / s with an error in the range of 5-15% relative,
the accuracy of determining the content of elements from induced and natural radioactivity corresponds to the accuracy obtained in the prototype.

 However, the third position is satisfied only under the condition of strict stabilization of the pulsed source of fast neutrons in each measurement cycle. When the source is shifted by 5 cm during the irradiation process, the accuracy of quantitative measurements decreases by about 20-30%. Thus, the proposed method and device for neutron activation logging and a device for its implementation provide a significant expansion of analytical capabilities, increase the accuracy of quantitative determination of elements and at the same time make it possible to identify and quantify the parameters of formation fluid flow through a well or annular space. The methodological possibilities of the method and device considered provide a real basis for solving the most important applied problems, especially at the stage of development of oil fields, where complex information is needed on flows and their parameters, the position of oil-water saturated layers, their current productivity, etc.

Claims (2)

1. The method of neutron activation logging, including discrete irradiation of rocks with a neutron flux from a pulsed neutron generator and continuous registration of induced gamma radiation (N ₁ ) in the intervals of 20 to 40 cm in length of symmetrically irradiated points and subsequent determination of the content of elements by the intensity of spectral flux recorded in characteristic areas of the energy spectrum, characterized in that the irradiation is carried out cyclically with continuous movement of the downhole tool with about the optimal speed V, for which, in each cycle, the pulsed neutron generator is synchronously moved with the logging speed in the direction opposite to the movement of the downhole tool, at a distance from the gamma-ray detector l ₁ t _p • V then return it to its initial position at a distance from the gamma-ray detector quanta l ₂ V (t _p + t _a), where t _n and t _a correspondingly calculated values and the pause activation established from the condition of registration of the induced effect i-th isotope with minimum statistical error, and additional measurements performed Ia spectral flux-16 isotope of nitrogen (N ₂₎ induced by gamma radiation as a function of time t with the quantization step May 1 with using a second gamma detector,
located above the pulsed neutron generator at a distance of l 40 100 cm and moving synchronously with it, and the N ₂ f (t) flux is measured between fast neutron pulses with an initial time delay after each pulse of t 5 6 ms with a total exposure of measurements in the th / V cycle where h base free movement pulsed neutron generator and the second detector of gamma-rays on the rise time and the intensity of the spectral flux of activated nuclei isotope N-16 (N ₁₎ determine the rate of flow of formation fluid V _f l / t _p and ei relative intensity Q _i, where l a distance between the second gamma ray detector and a pulsed neutron generator, t _p the time of entry of the activated N ₂ flow to the second detector, measured from the start of exposure in each cycle. 2. A neutron activation logging device comprising a downhole tool with a ground control panel connected by a geophysical cable, the ground control panel comprising a pulse depth sensor, a pulse analyzer, a log recorder and a power supply unit for a pulsed neutron generator, wherein the output of the pulse depth sensor is connected to a log recorder, information the input of which is connected to the output of the pulse analyzer, the first input connected to the first core of the geophysical cable, the output of the pulse power supply unit the neutron generator is connected to the third core of the geophysical cable, the downhole tool consists of a guard housing with the first gamma-ray detector located in it, connected to the input of the first recording and transmitting circuit, at the output connected to the first core of the geophysical cable, a pulsed neutron generator, separated from the first gamma detector with a protective screen, characterized in that the ground-based remote control further comprises an n-bit pulse counter,
two-input exposure unit and a fixation scheme for the beginning of the irradiation - measurement cycle, the input of which is connected to the second core of the geophysical cable, and the output to the input "Zero setting" of the n-bit pulse counter and the second input of the exposure unit, the output of the pulse depth sensor is additionally connected to the second residential geophysical cable and an information input of an n-bit pulse counter, an output connected to the first input of the exposure unit, the output of which is connected to the blocking input of a pulse analyzer equipped with a second information with an input connected through a capacitance to the third core of the geophysical cable, the downhole tool further comprises a second gamma-ray detector, a second recording and transmitting circuit, a mobile system with a speed reducer and a micro winch, a reversible electric motor, a control unit for the mobile system, including a pulse depth sensor downhole tool
limit switch, blocking circuit, first and second n-bit pulse counters, n-bit digital comparator, n logic switches of zero and one, first and second digital-to-analog converters, comparison circuit and zero-organ amplifier, while the second gamma-ray detector and a pulsed source of fast neutrons are placed in a mobile system, and a gamma detector is placed above a pulsed neutron generator at a distance of 40-100 cm and, via flexible communication (such as telephone), a second register is connected capstan-transmitting circuit connected to the third output conductor logging cable, mobile system mechanically connected to the speed reducer with the motor and the reversing mikrolebedkoy, pulsed sensor output downhole tool depth is connected to the data input of the first n-bit pulse counter,
and its output is connected by a bus to the input of the first digital-to-analog converter, the output of the second n-bit pulse counter is connected by a bus to the first input of an n-bit digital comparator and the input of the second digital-to-analog converter, the output of the n-bit digital comparator is connected to the "Zero" inputs of the second n- the pulse counter and the second digital-to-analog converter, the outputs of the first and second digital-to-analog converters are connected to the first and second inputs of the comparison circuit, the output associated with the input the house of the zero-organ amplifier connected to the reversible electric motor by the output, the outputs of n logic zero level and unit switches are connected via the bus to the second input of the n-bit digital comparator, the output of the limit switch is connected to the "Zero setting" input of the first n-bit pulse counter, the first digital-to-analog converter and the first control input of the blocking circuit,
the second control input of which is connected to the output of the n-bit digital comparator, the output of the blocking circuit is connected to the input of the second n-bit pulse counter, and the input is connected to the second core of the geophysical cable.

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