Drilling in-situ lithium ore content measuring method and device based on pulsed neutron technology

Abstract

The invention discloses a drilling in-situ lithium ore content measuring method and device based on the pulsed neutron technology, the device comprises a pulsed neutron generator, a neutron detector, a gamma detector and electronic processing equipment, the measuring method comprises the steps that time spectrum information of detected neutrons at a drilling in-situ position is obtained, and the neutron life is calculated according to the time spectrum information; stratum macroscopic sections under different lithium ore grades are obtained through calculation according to the neutron lifetime; according to the relation equation of the stratum macroscopic section and the lithium content, calculation is conducted based on the stratum macroscopic section, and the scale lithium content is obtained; and performing scale calculation on the scale curve of the lithium content based on the distribution of the stratum macroscopic cross section to obtain the actual lithium ore grade distribution of the stratum. And according to the change condition of time spectrum attenuation under different borehole sizes, a borehole correction equation is established, and the borehole influence is corrected. And monitoring the content of hydrogen in the water-containing wellbore according to the gamma-ray energy spectrum, and correcting the influence of hydrogen characteristic peak counting on the water-containing wellbore.

Description

Technical Field

[0001] The invention belongs to the technical field of mineral measurement, and in particular relates to a method and a device for measuring the content of lithium ore in situ in a borehole based on pulse neutron technology. Background Art

[0002] Lithium is an important rare metal resource in the 21st century. It plays an important role in new energy vehicles, lithium batteries, aerospace, nuclear industry and other fields. Among them, mica minerals, lithium clouds and pyroxene minerals are the main minerals of solid lithium mines. They are generally of low grade, but due to their large output and easy mining, they are the main types of lithium mines currently mined. In the process of mining resources in lithium mines, the grade of lithium ore can directly reflect the quality of the ore. Therefore, in-situ grade measurement of lithium ore in the mine is used to guide the actual mining of lithium ore resources, which will greatly improve the mining efficiency of lithium ore and enhance the productivity and production benefits of lithium resources in the mine.

[0003] At present, the methods for measuring lithium ore grade are mainly divided into field methods and laboratory methods. Among them, the field analysis method includes laser induced breakdown spectroscopy, which mainly uses a handheld laser induced breakdown spectrometer to analyze the surface of the core sample, and characterizes the lithium ore grade of the ore layer through the core measurement results. The analysis is simple and fast, and a large number of samples can be analyzed in a short time. However, the instrument cost is high and it is also relatively complex. It is difficult to obtain standard reference materials that completely match the matrix. The matrix effect is large, the laser scattering background interference is large, and the accuracy and precision are greatly affected by the uniformity of the sample. It is impossible to accurately characterize the grade and distribution of underground lithium ore. Laboratory methods mainly include inductively coupled plasma emission spectroscopy and spark source emission spectroscopy. These methods can accurately analyze samples taken from core samples, but they are affected by many factors such as the drilling sampling rate, the size of selective wear, the randomness of splitting and shrinking, etc., resulting in the high accuracy of core analysis, but its representativeness of the actual grade of underground ore layers is limited. Therefore, there is an urgent need for an in-situ grade measurement method for lithium ore to effectively characterize the grade and distribution of underground lithium ore, determine the size and exact boundaries of mineralization and the grade of the ore being processed, guide the actual production strategy of the mine, and improve the mining efficiency of the mine, which is crucial for calculating the mineral reserves to maintain mine operations in the future.

[0004] In 1956, the principle of pulse logging was first proposed, and downhole instrument design and testing work was carried out. With the development of neutron logging technology, it has also been well applied in petroleum, uranium and metal minerals. Among them, neutron lifetime logging, as a neutron measurement method, was first widely used in the field of oil and gas measurement. It mainly uses a DT pulse neutron source to emit 14MeV fast neutrons into the formation in a short period of time. The fast neutrons react with the nuclei in the borehole and formation and slow down to thermal neutrons within a few microseconds. Therefore, a thermal neutron radiation field is formed around the neutron source within 10-50μs after the fast neutron is emitted, and then it is captured and disappears by the nuclei in the formation. Neutron capture is a statistical probability problem. The more captured nuclei, the larger the thermal neutron capture cross section (abbreviated as sigma or Σ), and the greater the probability of neutrons being captured quickly. The average lifetime of a thermal neutron in a vacuum is about 15 minutes, but in common earth materials, due to the differences in the neutron absorption capacity of each element, the average lifetime of a neutron will show great differences in different strata. For example, the neutron lifetime in rock salt is about 5μs, while quartzite may be 900μs. Lithium has a large thermal neutron absorption cutoff, so when the stratum contains lithium, the lifetime of the neutron in the stratum will be greatly shortened, and as the lithium content of the stratum increases, the thermal neutron lifetime also decreases. Therefore, the neutron lifetime can effectively characterize and measure the low-grade lithium elements in the stratum. However, the above technical solution does not provide a method for measuring the in-situ lithium ore content in the borehole, and the underground lithium ore layer grade information calculated in the prior art is quite different from the actual underground ore layer. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a method for measuring the content of lithium ore in situ in a borehole based on pulsed neutron technology to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above object, the present invention provides a method for measuring the content of lithium ore in situ in a borehole based on pulsed neutron technology, comprising:

[0007] Acquire time spectrum information of neutron detection in situ in the borehole, wherein the time spectrum includes time and corresponding neutron counts;

[0008] Performing time window interception on the time spectrum information; calculating the neutron lifetime based on the intercepted time spectrum information by using a time spectrum method;

[0009] According to the neutron lifetime, a macroscopic cross section of the formation under different lithium ore grades is calculated; according to the relationship equation between the macroscopic cross section of the formation and the lithium content, a calculation is performed based on the macroscopic cross section of the formation to obtain the scaled lithium content;

[0010] The scaled lithium content is located according to the distribution of the macroscopic cross-section of the formation, and the calibration curve of the scaled lithium content is calculated according to the positioning result to obtain the actual lithium ore grade distribution of the formation.

[0011] Optionally, the process of obtaining time spectrum information of neutron detection in situ in the borehole includes:

[0012] Pulsed neutrons are emitted by a pulsed neutron emitter to bombard the formation, and the time spectrum curve of the neutrons, that is, the time spectrum information, is collected by a neutron detector.

[0013] Optionally, the process of performing time window interception on the time spectrum information includes:

[0014] In the time spectrum information, the starting time when the neutrons begin to decay to a certain threshold and the neutron count in the wellbore thereafter is lower than the count of the time spectrum is taken as the interception start time, and the time corresponding to when the count of the time spectrum is 0 is taken as the interception end time. A time window is set by using the interception start time and the interception end time, and the time spectrum information is intercepted through the time window.

[0015] Optionally, the process of obtaining the neutron lifetime includes:

[0016]

[0017] Among them, C(t) is the neutron count in the time spectrum information, τ is the neutron lifetime of the formation, 1 / τ is the attenuation coefficient, t is the time, and A is the decay term.

[0018] Optionally, the process of obtaining the formation macro-section includes:

[0019]

[0020] Among them, ∑ is the macroscopic cross section of the formation, τ is the neutron lifetime of the formation, and V is the thermal neutron velocity.

[0021] Optionally, the relationship between the macroscopic cross section of the formation and the lithium content is:

[0022] G li =K*Σ mes -F

[0023] Among them, G li is the calibration lithium ore content, K is the calibration coefficient, ∑ mes is the macroscopic cross section of the formation measured and calculated, and F is the contribution coefficient of the formation skeleton.

[0024] Optionally, before calculating based on the formation macroscopic cross section, the method further includes:

[0025] Obtaining a probe tube formation macroscopic cross section, wherein the probe tube formation macroscopic cross section is a macroscopic cross section in the formation simulated by a borehole test of a probe tube radius of a neutron emitter;

[0026] A well logging model and a lithium ore formation model are established through the model, and the ratios of different formation macro sections to the probe formation macro sections are calculated according to the well logging model and the lithium ore formation model to obtain correction coefficients of different formation macro sections;

[0027] The formation macro-section is corrected by using the corresponding correction coefficient to obtain the corrected formation macro-section for subsequent calculations.

[0028] Optionally, after obtaining the time spectrum information, the following steps are also included:

[0029] By establishing a well logging model and a lithium ore formation model, the characteristic peak area of ​​the hydrogen capture gamma spectrum and the response law of the wellbore water correction coefficient are calculated according to the well logging model and the lithium ore formation model;

[0030] The gamma detector is used to obtain the hydrogen capture gamma spectrum, and the borehole water correction coefficient is calculated by the response law according to the characteristic peak area of ​​the hydrogen capture gamma spectrum. The attenuation coefficient in the time spectrum information is adjusted by the borehole water correction coefficient to achieve the correction of the influence of water-containing boreholes.

[0031] In order to better achieve the above technical objectives, the present invention also provides a device for measuring the content of lithium ore in situ in a borehole based on pulsed neutron technology, comprising:

[0032] Pulsed neutron generator, neutron detector, gamma detector and signal processing electronic equipment, wherein the pulsed neutron generator adopts deuterium-deuterium or deuterium-tritium pulsed neutron generator, and the neutron detector adopts 3 He neutron detector. A pulsed neutron generator, a neutron detector, a gamma detector and an electronic processing device are arranged in the probe tube, and the neutron detector collects the neutron time spectrum information of the pulsed neutron emitter bombarding the formation, and the signal processing electronic device is used to execute the above-mentioned method for measuring the content of lithium ore in situ in the borehole based on the pulsed neutron technology.

[0033] Optionally, a gamma detector is used, wherein the gamma detector adopts a lanthanum bromide gamma detector, a sodium iodide gamma detector, a cerium bromide gamma detector or a bismuth germanate gamma detector, and the gamma detector is arranged in a probe tube to measure the hydrogen capture gamma energy spectrum.

[0034] Compared with the prior art, the present invention has the following advantages and technical effects:

[0035] The present invention proposes an in-situ lithium ore grade measurement method based on pulsed neutron logging technology. This method is different from the existing measurement method. It can obtain continuous and complete underground ore grade information, and the lateral detection radius is larger than the core radius, which can effectively eliminate the interference of objective and subjective factors in the process of drilling coring and splitting sample analysis. The underground lithium ore grade information provided is closer to the real underground ore layer, and the lithium ore grade in the mined rock can be effectively measured in the blasting hole during the mining process.

[0036] The present invention establishes a saturated lithium ore model through simulation, obtains the neutron time spectrum attenuation coefficient under strata with different lithium ore grades, calculates the corresponding stratum macroscopic cross-section, establishes the relationship equation between lithium ore grade and stratum macroscopic cross-section, obtains the calibration curve of lithium ore grade and stratum macroscopic cross-section, and makes corrections for the influence of wellbore size and the influence of hydrogen in wellbore water. Preliminary results show that pulsed neutron logging technology can effectively measure and characterize the grade and distribution of underground lithium ore. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0038] Figure 1 A schematic diagram of the neutron logging principle and the corresponding neutron time spectrum according to an embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of a lithium ore saturation model simulation according to an embodiment of the present invention;

[0040] Figure 3 A schematic diagram of the height and radius of a lithium ore saturation model according to an embodiment of the present invention;

[0041] Figure 4 Schematic diagram of neutron diffusion and noise time spectrum in a wellbore in the time spectrum results of different lithium contents in an embodiment of the present invention;

[0042] Figure 5 It is a schematic diagram of time spectrum fitting and corresponding calibration equation of different lithium ore contents in an embodiment of the present invention;

[0043] Figure 6 Schematic diagram of the effect of wellbore size on time spectrum according to an embodiment of the present invention;

[0044] Figure 7 A schematic diagram of a wellbore size correction equation and a corresponding wellbore influence correction effect according to an embodiment of the present invention;

[0045] Figure 8 It is a schematic diagram of a water-bearing wellbore correction equation and a corresponding water-bearing wellbore gamma spectrum simulation result according to an embodiment of the present invention;

[0046] Fig. 9 It is a schematic diagram of the gamma correction equation of a water-bearing wellbore and the corresponding correction effect of the water-bearing wellbore influence according to an embodiment of the present invention;

[0047] Fig.10 A schematic diagram of a lithium mine logging curve simulation according to an embodiment of the present invention;

[0048] Fig.11 Schematic diagram of a method for measuring in-situ lithium ore content in a borehole based on pulsed neutron technology according to an embodiment of the present invention. DETAILED DESCRIPTION

[0049] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0050] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0051] In-situ measurement of lithium ore in boreholes can effectively guide the mining strategy of lithium ore resources in mines and improve the efficiency of lithium ore mining. It is urgent to develop an in-situ measurement method for boreholes. Since natural lithium has a high thermal neutron absorption cross section, neutrons are ideal probes for lithium ore measurement.

[0052] The present invention is based on pulsed neutron technology, uses a pulsed neutron emitter to launch pulsed neutrons to bombard the formation, and collects neutron time spectrum through a neutron detector to establish a new neutron logging method for in-situ lithium ore measurement in boreholes. The simulation determines that the fitting time window in the neutron time spectrum is 352-2000μs; the minimum radius and height of the lithium ore saturation model are 60cm and 140cm respectively; the time window information of the neutron time spectrum with different lithium contents is in a good linear relationship with the lithium content, which verifies the above method. In addition, the gamma energy spectrum collected by the gamma detector in the probe can correct the size of the borehole and the influence of water in the borehole, and the relative error after correction is less than 5%. Through the measurement and analysis of lithium ore layers of different thicknesses and different contents in the simulated well, the layer thickness can reach 10cm, and the lithium content analysis results are consistent with the theoretical value, which verifies that the pulsed neutron technology can realize the in-situ measurement and layer analysis of lithium ore in the ground. It has guiding significance for the research and development of lithium ore content measurement methods and equipment in the in-situ of the borehole.

[0053] A detailed description of the above related contents is given below:

[0054] 1 Theory of in-situ quantitative method for lithium ore using pulsed neutron technology

[0055] 1.1 Neutron lifetime logging

[0056] During the logging process, according to the above neutron lifetime logging principle, the formation response thermal neutron time spectrum curve is obtained by using the neutron detector. The principle and curve results are as follows: Figure 1 As shown in the figure, at time t0, the neutron source is turned on, and the thermal neutron group continues to increase until the neutron source is turned off at time t1. After the neutron source is turned off, the thermal neutron group disappears rapidly, mainly because the fluid in the wellbore absorbs the thermal neutrons until the later stage (>t2) when the thermal neutrons in the borehole completely disappear. The extinction approximation at this time is the decay exponent, that is, a straight line on the semi-logarithmic graph (such as Figure 1 b), the slope of the second half of the curve is inversely proportional to the life time.

[0057] Since after the neutron burst, the neutrons in the formation decay like radioactive decay, the number of neutrons captured per unit time is proportional to the number of neutrons present. In the case of a homogeneous medium, the total number of neutrons in the formation process can be expressed as a function of time using formula (1):

[0058] N=N0·e -ΣVt #(1)

[0059] Where N is the number of neutrons at any time t; N0 is the number of neutrons at t=0; V is the velocity of neutrons; Σ is the macroscopic cross-section of the formation.

[0060] Because in the time spectrum, the relationship between the thermal neutron count C(t) in the time spectrum information and time t satisfies the exponential decay law:

[0061]

[0062] Where τ is the neutron lifetime of the formation, 1 / τ and are the exponential decay rates of the associated decay terms, t is the time, and A is the magnitude of the decay term.

[0063] According to formula (2), the formation neutron lifetime τ can be calculated using time spectrum technology, and combined with formula 1, the formation Σ calculation formula can be obtained as follows:

[0064]

[0065] Where V is the thermal neutron velocity. In actual well logging, the thermal neutron velocity is usually set to 2.2×10 5 cm / s, the unit of Σ is cu(10 -3 cm), and the unit of neutron lifetime is μs (10 -6 seconds), so formula (3) can be written as:

[0066]

[0067] From the above theory, we know that neutrons burst out at time t0 and end at time t1. The first area that has a greater impact on thermal neutron attenuation is the mixed area of ​​the borehole formation. The exponential decay rate changes over time. As the neutron diffuses, the borehole effect weakens and enters the single formation effect area, the exponential decay rate, that is, the attenuation coefficient, remains almost unchanged. Therefore, the key to obtaining accurate formation Σ is to select a suitable time period in the time spectrum to reduce the influence of the mixed area of ​​the borehole and formation effects, obtain a single formation effect area, and calculate the formation macroscopic cross section Σ, that is, the macroscopic capture cross section.

[0068] The present invention adopts a delayed measurement method. After a certain delay time has passed after the neutron release ends, the delay time is obtained by time spectrum analysis to determine the appropriate parameter t2. After determining the parameter t2, the fitting time window ΔW (t2-2000μs) is determined. The attenuation part of the time window is subjected to negative exponential fitting according to formula (2) to obtain the neutron lifetime τ of the formation, and then the formation macroscopic cross section Σ under different lithium ore grades is calculated.

[0069] According to this method, the relationship equation between the macroscopic cross section and the lithium content can be established:

[0070] G li =K*∑ mes -F#(5)

[0071] Among them G li is the calibration lithium ore content (%), K is the calibration coefficient, ∑ mes is the macroscopic cross section of the formation measured and calculated, and F is the contribution coefficient of the formation skeleton.

[0072] Finally, the underground lithium ore layer distribution is accurately located through the distribution curve of the macroscopic cross-section of the logging formation to generate a calibration curve, and the actual lithium ore grade distribution of the formation is calculated through the calibration curve.

[0073] 1.2 Prompt Gamma Neutron Activation Analysis (PGNAA) Technology

[0074] In the process of neutron lifetime logging, Figure 1As shown in the schematic diagram, when a neutron source is used to induce a large number of fast neutrons into the formation, these neutrons will lose energy through elastic and inelastic collisions with the nuclei of the nuclei in the drilling area. These collisions will continue until the neutrons and the surrounding matter reach a thermal equilibrium of about 0.025eV. These thermal neutrons will eventually be captured by the formation and borehole elements, and emit a large number of characteristic gamma rays with energies of about 0-10MeV according to the type of element. The formation elements are measured and analyzed using the gamma energy spectrum. This method is called the instantaneous gamma neutron activation analysis logging (PGNAA) technology. Since hydrogen nuclei have a large capture cross section for thermal neutrons during neutron logging, when there is water in the borehole, the hydrogen element in the water will have a greater impact on the attenuation coefficient of the time spectrum, thereby affecting the final lithium ore grade measurement results. Since H will release a characteristic gamma of 2.23MeV when capturing thermal neutrons, the present invention integrates the PGNAA technology to monitor the characteristic gamma counts of the H element in the borehole, which is used to correct the contribution of water in the borehole to the attenuation coefficient of the neutron time spectrum.

[0075] 1.3 Monte Carlo simulation method

[0076] The study used the Monte Carlo method to refer to the actual logging model, and established the uranium fission prompt neutron logging tool model of the ratio of epithermal neutrons to thermal neutrons and the cylindrical saturated lithium ore formation model, such as Figure 2 As shown. The outer diameter of the probe is 6cm, and the length of the probe is 170cm. The pulsed neutron source uses a 14MeV DT pulsed neutron source, with a pulse width of 200μs and a time spectrum period of 2000μs. The two detectors are arranged in an upper and lower structure, with the upper one 3 He neutron detector, used for thermal neutron (energy range 0.0001 ~ 0.1eV) time spectrum acquisition; below is the lanthanum bromide gamma detector, used for gamma spectrum acquisition. Neutron source and 3 The source distance between the center of the He thermal neutron detector is 27cm; the source distance between the neutron source and the center of the lanthanum bromide gamma detector is 45cm. According to the grade of the main hard rock lithium ore in Jiangxi Province, the lithium content of the hard rock lithium ore in the formation is set to be 0%, 0.1%, 0.2%, 0.4%, and 0.6%, respectively, and the bedrock is silicon dioxide. Since the time spectrum is mainly the influence of the borehole material on the neutron time spectrum within a period of time after the neutron pulse ends, the neutron imp in the borehole is set to 1 through the MCNP simulation, and the elapsed time spectrum of the neutrons in the borehole is recorded through the neutron detector, and the time spectrum results of the diffusion of neutrons from the borehole to the formation are recorded through the F4 card. The range of the time spectrum fitting curve is determined by comparing the elapsed time spectrum of the neutrons in the borehole source, the time spectrum of the diffusion to the formation, and the full neutron spectrum of the borehole formation. By changing the size of the borehole r in the model, the change of the neutron time spectrum attenuation coefficient of the same grade lithium ore under different borehole environments is simulated, and the elements in the borehole are filled with water to simulate the influence of the water-containing borehole on the neutron time spectrum attenuation coefficient.

[0077] It should be noted that the pulsed neutron generator can use not only the deuterium-tritium (DT) pulsed neutron generator, but also the deuterium-deuterium (DD) pulsed neutron generator. 3 He neutron detectors and gamma detectors can use not only lanthanum bromide gamma detectors, but also sodium iodide gamma detectors, cerium bromide gamma detectors or bismuth germanate gamma detectors.

[0078] 2 Results and discussion

[0079] 2.1 Lithium ore saturation model

[0080] In well logging, the height and diameter of the cylindrical model ore layer must be large enough to ensure that the size of the ore layer is a saturated ore layer for the detector. In this way, in a thick ore layer with uniform content, the neutron time spectrum attenuation coefficient of the adjacent measuring points in the center can reach a stable value, that is, the attenuation coefficient of the center point does not change with the thickness of the ore layer. Therefore, the measurement results of the neutron detector under this ore layer model are the same as those of the infinitely large ore layer. Through the MCNP method, the size of the ore layer model is gradually increased while the detector performance, source term, borehole and formation medium remain unchanged, and the changes in neutron counts detected by the detector are recorded. Figure 3 shown.

[0081] Neutron detection counts Figure 3 It can be observed that as the radius H of the logging model increases, the number of neutrons detected by the neutron logging instrument increases, and after the model height reaches a certain value, the neutron count basically does not change with the increase of the model height. Therefore, from the simulation results, it can be known that the height H of the saturated ore layer should be greater than or equal to 140cm. The change of neutron count value with the model radius is shown in the figure below. Figure 3 As shown in the figure, it can be observed that: as the height R of the logging model increases, the neutron count value detected by the neutron logging instrument increases, and after the model reaches a certain height, the number of neutrons detected basically does not change with the increase of the model radius. Therefore, from the simulation results, it can be known that the height R of the saturated ore layer should be greater than or equal to 60cm.

[0082] Through simulation, it was determined that the height of the saturated lithium ore model should be greater than 140cm and the radius should be greater than 60cm. Under the ore layer model of this size, the measurement results of the neutron detector are the same as those of the infinitely large ore layer. It is also the effective formation range size detected by the neutron logging instrument. The calculated formation Σ value is the total macroscopic cross-section of the saturated ore layer size and is not affected by the formation area outside the model size.

[0083] 2.2 Time window parameters

[0084] The results of borehole source neutron attenuation, borehole diffusion neutron time spectrum and time spectrum under different lithium content in the formation are as follows: Figure 4When the borehole source neutron attenuation is greater than 95%, it can be considered that the impact on the formation time spectrum is small. 95% can be used as a certain threshold to determine the interception start time. At the same time, the certain threshold can be determined based on relevant artificial experience, for example, Figure 4 For example, it can be seen that after 352μs, the source neutrons in the wellbore have decayed by 97.8%, and from the time spectrum of neutrons diffused from the wellbore to the formation, the neutron count diffused after 352μs is lower than the count of the full time spectrum, indicating that after this moment, the attenuation contribution of the wellbore to the time spectrum is far less than the contribution of the formation. Therefore, the attenuation coefficient fitting time window is selected as 352μs-2000μs.

[0085] 2.3 Lithium ore content calibration equation

[0086] The time spectrum ΔW (352μs-2000μs) of different lithium contents was fitted with a negative exponential according to formula (1). The fitting results are as follows: Figure 5 As shown in a, the fitting effect is good, and according to formula (4), the formation macroscopic cross section Σ with different neutron lifetimes τ is calculated. Finally, the relationship curve between formation Σ and lithium content is established, as shown in Figure 5 As shown, it can be seen that there is an obvious linear relationship between the macroscopic cross-section of the stratum and the lithium content of the stratum. The linear fitting equation for the lithium ore content based on the macroscopic cross-section of the stratum is obtained as follows:

[0087] G li =0.0058·∑ mes -0.06487

[0088] where Σ mes is the macroscopic cross section of the formation calculated during the actual measurement process, G li is the lithium ore grade. Fitting coefficient R 2 It is 0.999, F=0.06487.

[0089] 2.4 Wellbore size correction

[0090] In well logging, different aperture sizes will lead to different time spectra measured under the same mineral layer, resulting in inaccurate calibration results of the calibration equation. Therefore, it is necessary to correct the measurement results under different borehole radius. The neutron macroscopic cross section of the mineral layer simulated by borehole measurement at the probe radius size is recorded as Σ E , the macroscopic cross section of the formation tested in different wells is recorded as Σ x , then Σ E With Σ x The ratio of is defined as the wellbore size parameter correction:

[0091]

[0092] The Σ measured under different borehole radius conditions needs to be corrected to the Σ under the logging tool calibration environment, so as to obtain the accurate lithium content using the calibration equation obtained by the calibration curve. The corrected Σ cos for:

[0093] Σ cos =Σ E =μ r *Σ X

[0094] Assuming the lithium grade of the rock formation is 0.2%, the boreholes are set to 5cm to 12cm respectively, and the simulated neutron time spectrum results are as follows Figure 6 As shown in Figure 2, it can be seen that as the borehole becomes larger, the time spectrum attenuation coefficient gradually increases, and the macroscopic absorption cross section of neutrons in the formation gradually decreases.

[0095] According to the above method, the correction coefficient μ is obtained by calculation r The equation for the wellbore radius is Figure 7 As shown. It can be seen that the borehole radius and the correction coefficient have a good linear relationship. The correction coefficient equation is used to correct the measurement results under different borehole radii, and the final lithium ore content calibration results are obtained, as shown in Figure 7 As shown, it can be seen that the correction equation can effectively correct the calibration results under different wellbore radii. After correction, the calibration deviation of lithium ore content is less than 5%, and the effect is good.

[0096] 2.5 Wellbore water correction

[0097] During the logging process, especially water accumulation in open-pit blasting holes will have a great impact on the logging results, so it is necessary to correct the water-bearing wellbore. Since hydrogen capture gamma is the gamma ray released by the radiation capture reaction between thermal neutrons and hydrogen, its energy peak is between 2 and 2.4 MeV. It is 10 -6 ~10 -3 The size of the hydrogen capture gamma count can indicate the content within the detector range. Based on the relative relationship between hydrogen capture gamma and the hydrogen content in the borehole and saturated ore layer, the gamma detector is used to measure the hydrogen capture gamma energy spectrum, and the hydrogen capture gamma characteristic peak area and the borehole water correction coefficient μ are obtained. W The response law of the wellbore water is realized by in-situ correction, and the correction coefficient μ W The calculation formula is:

[0098]

[0099] Among them A N is the characteristic peak area of ​​hydrogen capture gamma in different water-containing wells, A B The characteristic peak area of ​​hydrogen capture gamma in the dry pore state is a constant. Finally, according to the relationship between the characteristic peak area of ​​hydrogen capture gamma and μW The relationship between the gamma ray spectrum and the water-bearing wellbore is used to fit the correction equation, and the influence of the characteristic peak of the hydrogen peak of the gamma ray spectrum under different water-bearing wellbore on the water-bearing wellbore can be corrected according to the correction equation.

[0100] Gamma spectra of different boreholes under simulated water content conditions are as follows Figure 8 As shown in Figure 2, it can be seen that as the borehole radius increases, the time spectrum attenuation coefficient of the water in the borehole changes significantly. Fig. 9 It can be seen that with the increase of water content, the area of ​​hydrogen characteristic peak is also gradually increasing.

[0101] According to the above borehole correction equation, the characteristic peak counts of hydrogen 2-2.4 MeV are obtained, and the relationship curve between hydrogen peak counts and correction coefficients is established, as shown in Fig. 9 As shown in (a), it can be seen that the H characteristic gamma peak count and the correction coefficient have a good exponential relationship. The equation of hydrogen characteristic peak count and correction coefficient is obtained by fitting. Finally, the time spectrum measurement results of different water-bearing wells are corrected according to this correction equation. Fig. 9 As shown in (b), it can be seen that the corrected lithium ore grade is within the 5% error band of the true value, and the correction effect is good.

[0102] 2.6 Well logging curve simulation

[0103] Finally, a lithium ore neutron logging model with different ore layer thicknesses was established, and a cylindrical formation model with a height of 16 meters was designed according to the size of the simulated saturated model. Fig.10 As shown, the bedrock in the 1st, 3rd, 5th, 7th and 10th layers from top to bottom is silica bedrock, the minimum thickness of the lithium-bearing ore layer is 70cm (layer 4), and the 8th layer is the largest ore layer of two meters. The neutron logging model was moved in the borehole of this stratum, and a total of 160 points were measured with an interval of 10 cm. The neutron time spectrum was measured at different positions, and the time spectrum attenuation coefficient at different positions was fitted using the calculation method introduced above, and Σ was calculated. The lithium grade was calculated through the calibration equation and compared with the theoretical value, as shown in the figure. Fig.10 As shown in the figure, it can be seen that the calculated results (area filling and) are in good agreement with the theoretical values ​​(curves). However, in the boundary area, the propagation and attenuation characteristics of neutrons in the strata are affected by the surrounding layers. This interference is more significant in thin strata, resulting in a decrease in the accuracy of the ore boundary measurement results. From the simulation results, it can be seen that the distance of the interlayer influence is about 70cm.

[0104] 3 Conclusion

[0105] This paper proposes a method and device for determining the lithium grade of a formation by using pulsed neutron logging technology through the macroscopic cross section (neutron lifetime) of thermal neutron absorption in the formation. The measuring device consists of a DT neutron generator, a He3 neutron detector, a lanthanum bromide gamma detector and corresponding electronic parts. The method flow chart is shown in the figure below. Fig.11 The size of the saturated lithium ore model was determined by Monte Carlo simulation: R>60cm, H>140cm. The neutron time spectrum response of different lithium ore grades simulated in the model showed that there is a linear relationship between lithium ore grade and nuclear physical parameters (Σ). The linear scale equation is: G li =0.0058·Σ mes -0.0648, R 2 =0.999, and the grade of lithium ore in the formation was determined by this scale equation. The influence of borehole radius was corrected during logging, and the influence of borehole water was corrected by combining gamma spectrum information. The relative errors before and after correction were less than 5%. Finally, a 16m lithium-bearing ore layer logging case was simulated. The comprehensive logging results showed that this borehole logging method is feasible for in-situ measurement of lithium ore grade, and provides a new method for in-situ measurement of lithium ore grade in mine blasting holes.

[0106] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for measuring the content of lithium ore in situ in a borehole based on pulsed neutron technology, characterized in that: include: Acquire time spectrum information of neutron detection in situ in the borehole, wherein the time spectrum includes time and corresponding neutron counts; Performing time window interception on the time spectrum information; calculating the neutron lifetime based on the intercepted time spectrum information by using a time spectrum method; According to the neutron lifetime, a macroscopic cross section of the formation under different lithium ore grades is calculated; according to the relationship equation between the macroscopic cross section of the formation and the lithium content, a calculation is performed based on the macroscopic cross section of the formation to obtain the scaled lithium content; The scaled lithium content is located according to the distribution of the macroscopic cross-section of the formation, and the calibration curve of the scaled lithium content is calculated according to the positioning result to obtain the actual lithium ore grade distribution of the formation.

2. The method according to claim 1, characterized in that The process of obtaining the time spectrum information of neutron detection in situ in the borehole includes: Pulsed neutrons are emitted by a pulsed neutron emitter to bombard the formation, and the time spectrum curve of the neutrons, that is, the time spectrum information, is collected by a neutron detector.

3. The method according to claim 1, characterized in that The process of performing time window interception on the time spectrum information includes: In the time spectrum information, the starting time when the neutrons begin to decay to a certain threshold and the neutron count in the wellbore thereafter is lower than the count of the time spectrum is taken as the interception start time, and the time corresponding to when the count of the time spectrum is 0 is taken as the interception end time. A time window is set by using the interception start time and the interception end time, and the time spectrum information is intercepted through the time window.

4. The method according to claim 1, characterized in that: The process of obtaining the neutron lifetime includes: Among them, C(t) is the neutron count in the time spectrum information, τ is the neutron lifetime of the formation, 1 / τ is the attenuation coefficient, t is the time, and A is the decay term.

5. The method according to claim 1, characterized in that The process of obtaining the macroscopic cross section of the formation includes: Among them, ∑ is the macroscopic cross section of the formation, τ is the neutron lifetime of the formation, and V is the thermal neutron velocity.

6. The method according to claim 1, characterized in that The relationship equation between the macroscopic cross section of the formation and the lithium content is: G li =K*∑ mes -F Among them, G li is the calibration lithium ore content, K is the calibration coefficient, ∑ mes is the macroscopic cross section of the formation measured and calculated, and F is the contribution coefficient of the formation skeleton.

7. The method according to claim 1, characterized in that Before calculating based on the macroscopic cross section of the formation, the following steps are also included: Obtaining a probe tube formation macroscopic cross section, wherein the probe tube formation macroscopic cross section is a macroscopic cross section in the formation simulated by a borehole test of a probe tube radius of a neutron emitter; Establishing a well logging model and a lithium ore formation model by simulation, calculating the ratio of different formation macro sections to the probe formation macro sections according to the well logging model and the lithium ore formation model, and obtaining correction coefficients of different formation macro sections; The formation macro-section is corrected by using the corresponding correction coefficient to obtain the corrected formation macro-section for subsequent calculations.

8. The method according to claim 1, characterized in that After obtaining the time spectrum information, it also includes: By establishing a well logging model and a lithium ore formation model, the characteristic peak area of ​​the hydrogen capture gamma spectrum and the response law of the wellbore water correction coefficient are calculated according to the well logging model and the lithium ore formation model; The gamma detector is used to obtain the hydrogen capture gamma spectrum, and the borehole water correction coefficient is calculated by the response law according to the characteristic peak area of ​​the hydrogen capture gamma spectrum. The attenuation coefficient in the time spectrum information is adjusted by the borehole water correction coefficient to achieve the correction of the influence of water-containing boreholes.

9. A device for measuring the content of lithium ore in-situ in a borehole based on pulsed neutron technology, characterized in that: include: Pulsed neutron generator, neutron detector, gamma detector and signal processing electronic equipment, wherein the pulsed neutron generator adopts deuterium-deuterium or deuterium-tritium pulsed neutron generator, and the neutron detector adopts 3 He neutron detector. A pulsed neutron generator, a neutron detector, a gamma detector and an electronic processing device are arranged in the probe tube, and the neutron detector is used to collect the neutron time spectrum information of the pulsed neutron emitter bombarding the formation, and the signal processing electronic device is used to execute the method for measuring the content of lithium ore in situ in a borehole based on the pulsed neutron technology as described in any one of claims 1 to 8.

10. The device according to claim 9, characterized in that Also includes: Gamma detector, the gamma detector adopts lanthanum bromide gamma detector, sodium iodide gamma detector, cerium bromide gamma detector or bismuth germanate gamma detector, the gamma detector is arranged in the probe tube, and is used to measure the hydrogen capture gamma energy spectrum.

Images