A method and device for measuring the content of lithium ore in-situ in a borehole based on pulsed neutron technology

Abstract

The application discloses a kind of based on pulse neutron technology's borehole in-situ lithium ore content measurement method and device, device includes pulse neutron generator, neutron detector, gamma detector and electronic processing equipment, measurement method includes: obtaining the time spectrum information of borehole in-situ place detection neutron, according to time spectrum information, neutron lifetime is calculated;According to the formation of different lithium ore grade under the macroscopic cross section of neutron lifetime calculation;According to the relationship equation of formation macroscopic cross section and lithium content, based on the calculation of formation macroscopic cross section, obtains scale lithium content;The calibration curve of lithium content is scaled based on the distribution of formation macroscopic cross section and scaled calculation, and the actual lithium ore grade distribution of formation is obtained.According to the change of time spectrum attenuation under different borehole size, wellbore correction equation is established, and the influence of wellbore is corrected.According to gamma energy spectrum, the content of hydrogen in water-containing wellbore is monitored, and the influence of water-containing wellbore is corrected according to hydrogen characteristic peak count.

Description

Technical Field

[0001] This invention belongs to the field of mineral measurement technology, and in particular relates to a method and device for measuring the content of lithium ore in situ through boreholes based on pulsed neutron technology. Background Technology

[0002] Lithium is an important rare metal resource in the 21st century, playing a vital role in new energy vehicles, lithium batteries, aerospace, and the nuclear industry. Mica-type minerals and pyroxene-type minerals are currently the most abundant minerals found in solid lithium deposits. While generally of lower grade, their large yields and ease of extraction make them the primary types of lithium mines. Since the grade of lithium ore directly reflects its quality, in-situ grade measurement of lithium ore is crucial for guiding actual lithium resource extraction. This significantly improves mining efficiency and enhances the productivity and profitability of lithium resources.

[0003] Currently, methods for measuring lithium ore grade are mainly divided into field methods and laboratory methods. Field analysis methods include laser-induced breakdown spectroscopy (LAS), which uses a handheld LAS spectrometer to analyze the surface of core samples. The core measurement results characterize the lithium grade of the ore layer. This method is simple and rapid, allowing for the analysis of large numbers of samples in a short time. However, the instruments are expensive and complex, it is difficult to obtain standard reference materials that perfectly match the matrix, the matrix effect is significant, and there is considerable interference from laser scattering background. Furthermore, the accuracy and precision are greatly affected by the homogeneity of the sample, making it unable to accurately characterize the grade and distribution of underground lithium ore. Laboratory methods mainly include inductively coupled plasma atomic emission spectrometry (ICP-AES) and spark source emission spectrometry (SSA). These methods can accurately analyze core samples, but they are affected by many factors such as drilling recovery rate, selective abrasion, and the randomness of sample splitting and reduction. While the accuracy of core analysis is relatively high, its representativeness of the actual grade of underground ore layers is limited. Therefore, there is an urgent need for in-situ lithium ore grade measurement methods to effectively characterize the grade and distribution of underground lithium ore, determine the size and exact boundaries of mineralization and the grade of ore being processed, guide actual mine production strategies, and improve mine mining efficiency. This is crucial for calculating the mineral reserves needed to sustain mine operations in the future.

[0004] With the development of neutron logging technology, it has been widely applied in petroleum, uranium, and metal mining. Neutron lifetime logging, as a neutron measurement method, was initially widely used in oil and gas measurement. It primarily utilizes a DT pulsed neutron source to emit 14 MeV fast neutrons into the formation within a short period. These fast neutrons undergo a series of reactions with atomic nuclei in the wellbore and formation, slowing down to thermal neutrons within microseconds. Therefore, a thermal neutron radiation field is formed around the neutron source within 10-50 μs after the fast neutron emission, after which the neutrons are captured and disappear by atomic nuclei in the formation. Neutron capture is a statistical probability problem; the greater the number of captured nuclei, the larger the thermal neutron capture cross-section (simply referred to as sigma or Σ), and the greater the probability of rapid neutron capture. The average lifetime of a thermal neutron in a vacuum is approximately 15 minutes. However, in common Earth materials, due to differences in the neutron absorption capacity of various elements, the average lifetime of a neutron varies greatly in different strata. For example, the neutron lifetime in rock salt is about 5 μs, while in quartzite it can be 900 μs. Lithium has a large thermal neutron absorption cutoff, so when a stratum contains lithium, the neutron lifetime in the stratum is greatly shortened. Furthermore, as the lithium content in the stratum increases, the thermal neutron lifetime also decreases. Therefore, neutron lifetime can be effectively used to characterize and measure low-grade lithium in strata. However, the above-mentioned technical solution does not provide a method for measuring the lithium content in boreholes in situ, and the grade information of underground lithium ore layers calculated in existing technologies differs significantly from the actual underground ore layers. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a borehole in-situ lithium ore content measurement method based on pulsed neutron technology, thereby resolving the issues present in the prior art.

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

[0007] Obtain time spectrum information of neutrons detected at the borehole in situ, wherein the time spectrum includes time and corresponding neutron count;

[0008] The time spectrum information is truncated by a time window; using the time spectrum method, based on the truncated data... The neutron lifetime was calculated.

[0009] Based on the neutron lifetime, the macroscopic cross-section of the formation under different lithium ore grades is calculated; based on the relationship equation between the macroscopic cross-section of the formation and the lithium content, the calibrated lithium content is calculated based on the macroscopic cross-section of the formation.

[0010] The lithium content of the scale is located based on the distribution of the macroscopic cross section of the strata, and the scale curve of the lithium content is calculated based on the location results to obtain the actual lithium ore grade distribution of the strata.

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

[0012] The formation is bombarded by pulsed neutrons emitted by a pulsed neutron emitter, and the time spectrum curve of the neutrons, i.e., time spectrum information, is collected by a neutron detector.

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

[0014] In the time spectrum information, the starting time when neutrons begin to decay to a certain threshold and the subsequent neutron count in the wellbore is lower than the time spectrum count is taken as the cutoff start time, and the time when the time spectrum count is 0 is taken as the cutoff end time. A time window is set by the cutoff start time and the cutoff end time, and the time spectrum information is cut off by the time window.

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

[0016]

[0017] in, τ represents the neutron count in the time spectrum information, τ represents the neutron lifetime of the formation, 1 / τ represents the decay coefficient, t represents time, and A represents the decay term.

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

[0019]

[0020] in, Let τ be the macroscopic cross section of the formation, τ be the neutron lifetime of the formation, and V be the thermal neutron velocity.

[0021] Optionally, the equation relating the macroscopic cross-section of the formation to the lithium content is as follows:

[0022]

[0023] in, The scale indicates the lithium ore content, and K is the scale coefficient. F represents the macroscopic cross section of the formation as measured and calculated, and F is the contribution coefficient of the formation skeleton.

[0024] Optionally, the calculation may further include the following steps before performing the calculation based on the macroscopic cross-section of the formation:

[0025] Obtain the macroscopic cross section of the formation using the probe, which is the macroscopic cross section of the formation simulated in the wellbore test with the probe radius of the neutron emitter;

[0026] A well logging model and a lithium ore formation model are established using a continuous model. Based on the well logging model and the lithium ore formation model, the ratio of different macroscopic cross sections of the formation to the macroscopic cross section of the probe formation is calculated to obtain the correction coefficients for different macroscopic cross sections of the formation.

[0027] The macroscopic cross section of the formation is corrected by the corresponding correction factor to obtain the corrected macroscopic cross section for subsequent calculations.

[0028] Optionally, after obtaining the time spectrum information, the following may also be included:

[0029] By establishing a well logging model and a lithium ore formation model, the response law of the characteristic peak area of ​​the hydrogen capture gamma spectrum and the well water correction coefficient is calculated based on the well logging model and the lithium ore formation model.

[0030] A hydrogen-captured gamma spectrum is acquired using a gamma detector. Based on the characteristic peak area of ​​the hydrogen-captured gamma spectrum, the wellbore water correction coefficient is calculated using the response law. This wellbore water correction coefficient is then used to adjust the attenuation coefficient in the time spectrum information, thereby correcting the impact on water-bearing wells.

[0031] To better achieve the above-mentioned technical objectives, the present invention also provides a borehole in-situ lithium ore content measurement device based on pulsed neutron technology, comprising:

[0032] The system includes a pulsed neutron generator, a neutron detector, a gamma detector, and signal processing electronics, wherein the pulsed neutron generator is a deuterium-deuterium or deuterium-tritium pulsed neutron generator, and the neutron detector is... 3 He neutron detector. A pulsed neutron generator, neutron detector, gamma detector, and electronic processing equipment are installed inside the probe. The neutron detector collects the neutron time spectrum information of the formation bombarded by the pulsed neutron emitter. The signal processing electronics are used to perform the above-mentioned in-situ borehole lithium content measurement method based on pulsed neutron technology.

[0033] Optionally, a gamma detector is used, which may be a lanthanum bromide gamma detector, a sodium iodide gamma detector, a cerium bromide gamma detector, or a bismuth germanate gamma detector. The gamma detector is placed inside the probe tube and is used to measure the hydrogen capture gamma spectrum.

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

[0035] This invention proposes an in-situ method for measuring lithium ore grade based on pulsed neutron logging technology. Unlike existing methods, this approach obtains continuous and complete underground ore grade information. Furthermore, its lateral detection radius is larger than the core radius, effectively eliminating interference from both objective and subjective factors during drilling, coring, and splitting analysis. The resulting underground lithium ore grade information more closely approximates the actual underground ore layer, enabling effective measurement of lithium ore grade in the mined rock during blasting operations.

[0036] This 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 macroscopic cross-section of the strata, establishes the relationship equation between lithium ore grade and macroscopic cross-section of the strata, obtains the scale curve of lithium ore grade and macroscopic cross-section of the strata, and corrects for the influence of wellbore size and hydrogen element in wellbore water. Preliminary results show that pulsed neutron logging technology can effectively measure and characterize the grade and distribution of underground lithium ore. Attached Figure Description

[0037] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0038] Figure 1 This is a schematic diagram of the neutron logging principle and 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 This is a schematic diagram showing the height and radius of the lithium ore saturation model according to an embodiment of the present invention;

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

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

[0043] Figure 6 This is a schematic diagram illustrating the effect of wellbore size on the time spectrum in an embodiment of the present invention;

[0044] Figure 7 This is a schematic diagram illustrating the wellbore size correction equation and the corresponding wellbore influence correction effect in an embodiment of the present invention;

[0045] Figure 8 This is a schematic diagram of the corrected equation for the water-bearing wellbore and the corresponding simulation results of the gamma spectral density of the water-bearing wellbore, according to an embodiment of the present invention.

[0046] Figure 9 This is a schematic diagram illustrating the gamma correction equation for water-bearing wells and the corresponding correction effect on the influence of water-bearing wells according to an embodiment of the present invention.

[0047] Figure 10 This is a schematic diagram of a lithium ore logging curve simulation according to an embodiment of the present invention;

[0048] Figure 11 This is a schematic diagram of the in-situ lithium ore content measurement method based on pulsed neutron technology in a borehole, according to an embodiment of the present invention. Detailed Implementation

[0049] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

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

[0051] In-situ borehole measurement can effectively guide lithium resource extraction strategies and improve lithium ore mining efficiency, thus necessitating the development of a borehole-based measurement method. Since natural lithium has a high thermal neutron absorption cross-section, neutrons are ideal probes for lithium ore measurement.

[0052] This invention, based on pulsed neutron technology, utilizes a pulsed neutron emitter to bombard the formation with pulsed neutrons, and a neutron time spectrum is acquired by a neutron detector, establishing a novel neutron logging method for in-situ borehole lithium ore measurement. Simulations determined the fitting time window in the neutron time spectrum to be 352-2000 μs; the minimum radius and height of the lithium ore saturation model were 60 cm and 140 cm, respectively; the time window information of the neutron time spectrum for different lithium contents showed a good linear relationship with the lithium content, validating the above method. Furthermore, the gamma spectrum acquired by the gamma detector in the probe can correct for the influence of borehole size and borehole water, with the corrected relative error being less than 5%. Measurement and analysis of lithium ore layers of different thicknesses and contents in simulated wells showed that the layer thickness could reach 10 cm, and the lithium content analysis results showed good consistency with the theoretical values, verifying that in-situ borehole lithium ore measurement and layer analysis based on pulsed neutron technology can be achieved. This provides guidance for the development of in-situ borehole lithium ore content measurement methods and equipment.

[0053] The above-mentioned content will be described in detail:

[0054] 1. Theoretical Method for In-situ Quantitative Analysis of Lithium Ore Using Pulsed Neutron Technology

[0055] 1.1 Neutron lifetime logging

[0056] During well logging, based on the aforementioned neutron lifetime logging principle, the formation response thermal neutron time spectrum curve obtained using a neutron detector is described below. The principle and curve results are as follows: Figure 1 As shown, at time t0, the neutron source is turned on, and the thermal neutron swarm continuously increases until the neutron source is turned off at time t1. After the neutron source is turned off, the thermal neutron swarm disappears rapidly, mainly because the fluid in the wellbore absorbs the thermal neutrons, until the thermal neutrons in the borehole completely disappear in the later stage (>t2). The exponent of this disappearance is the decay exponent, which is a straight line on the semi-logarithmic plot (as shown in the figure). Figure 1 As shown in b), the slope of the latter half of the curve is inversely proportional to the lifetime.

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

[0058]

[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 the neutrons; and Σ is the macroscopic cross section of the formation.

[0060] Because in the time spectrum, the thermal neutron count in the time spectrum information The relationship with time t follows an exponential decay law:

[0061]

[0062] Where τ is the neutron lifetime of the formation, 1 / τ is the exponential decay rate of the relevant decay term, t is 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 formula for calculating the formation Σ is:

[0064]

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

[0066]

[0067] As the above theory shows, neutrons erupt at time t0 and cease at time t1. The wellbore-formation mixing region has the greatest impact on thermal neutron decay initially, with the exponential decay rate changing over time. As neutron diffusion weakens the wellbore effect and enters a single formation effect region, the exponential decay rate, or decay coefficient, remains almost constant. Therefore, the key to obtaining accurate formation Σ is to select an appropriate time period in the time spectrum to reduce the influence of the wellbore and formation effect mixing region, obtain a single formation effect region, and calculate the macroscopic formation cross-section Σ, i.e., the macroscopic trapping cross-section.

[0068] This invention employs a delayed measurement method. After the neutron release ends, a certain delay time is allowed, which is obtained through time spectrum analysis. A suitable parameter t2 is determined, and after determining the parameter t2, the fitting time window ΔW(t2-2000μs) is determined. The decay portion of this time window is fitted with a negative exponential formula (2) to obtain the neutron lifetime τ of the formation, and then the macroscopic cross section Σ of the formation under different lithium ore grades is calculated.

[0069] Based on this method, the relationship equation between the macroscopic cross section and the lithium content can be established as follows:

[0070]

[0071] in The scale represents the lithium ore content (%), where K is the scale factor. F represents the macroscopic cross section of the formation as measured and calculated, and F is the contribution coefficient of the formation skeleton.

[0072] Finally, the distribution of underground lithium ore layers is accurately located by using the distribution curve of the macroscopic cross section of the well logging formation, so as to generate a scale curve, and the actual lithium ore grade distribution of the formation is calculated by using this scale curve.

[0073] 1.2 Transient Gamma Neutron Activation Analysis (PGNAA) Technique

[0074] In the process of neutron lifetime logging, such as Figure 1As shown in the schematic diagram, when a large number of fast neutrons are induced into the formation using a neutron source, these neutrons lose energy through elastic and inelastic collisions with atomic nuclei in the borehole area. These collisions continue until the neutrons reach thermal equilibrium with the surrounding matter at approximately 0.025 eV. These thermal neutrons are eventually captured by formation and borehole elements, emitting a large number of characteristic gamma rays with energies around 0-10 MeV, depending on the element. The formation elements are then measured and analyzed using gamma ray spectroscopy; this method is called transient gamma neutron activation analysis logging (PGNAA). Because hydrogen nuclei have a large capture cross-section for thermal neutrons during neutron logging, the presence of water in the borehole significantly affects the attenuation coefficient of the time spectrum, thus influencing the final lithium grade measurement results. Since H releases a characteristic gamma of 2.23 MeV when it captures thermal neutrons, this invention integrates PGNAA technology to monitor the characteristic gamma count of H in the wellbore, which is used to correct the contribution of water in the wellbore to the neutron time spectrum decay coefficient.

[0075] 1.3 Monte Carlo Simulation Method

[0076] The study used the Monte Carlo method to reference actual well logging models, establishing a uranium fission transient neutron logging tool model with an ultrathermal neutron to thermal neutron ratio and a cylindrical saturated lithium ore formation model, such as... Figure 2 As shown. The probe tube has an outer diameter of 6 cm and a length of 170 cm; the pulsed neutron source is a 14 MeV DT pulsed neutron source with a pulse width of 200 μs and a time spectral period of 2000 μs. The two detectors are arranged in an upper and lower structure, with the upper one being... 3 The helium neutron detector is used for thermal neutron (energy range 0.0001~0.1eV) time spectrum acquisition; below it is the lanthanum bromide gamma detector, used for gamma energy spectrum acquisition. Neutron source and 3 The source distance between the He thermal neutron detector center and the lanthanum bromide gamma detector center is 27 cm; the source distance between the neutron source and the lanthanum bromide gamma detector center is 45 cm. Based on the grades of major hard-rock lithium deposits in Jiangxi Province, this invention sets the lithium content of the hard-rock lithium deposits in the formation to be 0%, 0.1%, 0.2%, 0.4%, and 0.6%, with silica as the bedrock. Since the time spectrum is mainly influenced by borehole material during the period after the neutron pulse ends, the neutron imp in the borehole is set to 1 using MCNP simulation. The neutron ebb-out time spectrum in the borehole is recorded by the neutron detector, and the time spectrum of neutron diffusion from the borehole to the formation is recorded using an F4 card. The range of the time spectrum fitting curve is determined by comparing the neutron ebb-out time spectrum of the borehole source, the diffusion time spectrum to the formation, and the full neutron spectrum of the borehole and formation. By changing the size of the borehole r in the model, the change in the neutron time spectrum attenuation coefficient of lithium deposits of the same grade under different borehole environments is simulated. The element in the borehole is filled with water to simulate the influence of water-bearing wells on the neutron time spectrum attenuation coefficient.

[0077] It should be noted that, in addition to using an external deuterium-tritium (DT) pulsed neutron generator, a deuterium-deuterium (DD) pulsed neutron generator can also be used. The neutron detector employs... 3 In addition to lanthanum bromide gamma detectors, sodium iodide gamma detectors, cerium bromide gamma detectors, or bismuth germanate gamma detectors can also be used for he neutron detectors and 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 of the mineral layer must be large enough to ensure that the size of the layer is saturated for the detector. This allows the neutron time spectrum attenuation coefficient at the central location of a thick, uniformly distributed mineral layer to reach a stable value, meaning the attenuation coefficient at the center does not change with the layer thickness. Therefore, the measurement results of the neutron detector under this mineral layer model are the same as those of an infinitely large mineral layer. Using the MCNP method, with detector performance, source term, wellbore, and formation medium remaining constant, the size of the mineral layer model is gradually increased, and the changes in the neutron count detected by the detector are recorded as follows: Figure 3 As shown.

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

[0082] Simulations determined that the height of the saturated lithium ore model should be greater than 140cm and the radius should be greater than 60cm. Under this size of ore layer model, the measurement results of the neutron detector are the same as those of an infinitely large ore layer, which is also the effective layer range size detected by the neutron logging tool. 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 wellbore source neutron decay, wellbore diffused neutron time spectra, and time spectra under different lithium contents in the formation are as follows: Figure 4 As shown. When the neutron attenuation of the wellbore source is greater than 95%, its impact on the formation time spectrum can be considered relatively small. 95% can be used as a certain threshold to determine the cutoff start time. Simultaneously, a certain threshold can be determined based on relevant human experience, for example, using... Figure 4 For example, it can be seen that the source neutrons in the wellbore have decayed by 97.8% after 352μs. Moreover, looking at 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. This indicates that the contribution of the wellbore to the decay of the time spectrum after this moment is much smaller than the contribution of the formation. Therefore, the time window for fitting the decay coefficient is selected as 352μs-2000μs.

[0085] 2.3 Lithium Ore Content Calibration Equation

[0086] The time spectra ΔW (352μs-2000μs) with different lithium contents were fitted with a negative exponential curve according to formula (1), and the fitting results are as follows. Figure 5 As shown in a, the fitting effect is good, and the macroscopic cross section Σ of the formation with different neutron lifetimes τ is calculated according to formula (4). Finally, the relationship curve between formation Σ and lithium content is established, as shown in Figure 1. Figure 5 As shown, there is a clear linear relationship between the macroscopic cross section of the formation and the lithium content of the formation. Linear fitting yields the following lithium content calibration equation based on the macroscopic cross section of the formation:

[0087]

[0088] Where Σ mes G is the macroscopic cross section of the formation calculated during the actual measurement process. li This represents the lithium ore grade. The fitting coefficient R0 2 The value is 0.999, and F = 0.06487.

[0089] 2.4 Wellbore Size Correction

[0090] In well logging, different borehole diameters can lead to different time spectra measured under the same ore layer, resulting in inaccurate calibration results. Therefore, it is necessary to correct the measurement results for different borehole radii. The macroscopic cross section of the ore layer simulated by logging at boreholes with different probe radii is denoted as Σ. E The macroscopic cross-section of the formation tested at different wellbores is denoted as Σ. x , then Σ E With Σ x The ratio is defined as the wellbore size parameter correction:

[0091]

[0092] The Σ measured under different wellbore radii needs to be corrected to the Σ under the logging tool calibration environment in order to obtain an accurate lithium content using the calibration equation obtained from the calibration curve. for:

[0093]

[0094] With the lithium ore grade in the rock formation set at 0.2% and the wellbore depth set at 5cm~12cm, the simulated neutron time spectrum results are as follows: Figure 6 As shown, it can be seen that as the wellbore size increases, the time-spectrum attenuation coefficient gradually increases, while the macroscopic absorption cross section of formation neutrons gradually decreases.

[0095] Based on the above method, the correction coefficient μ is calculated. r The equation with respect to the wellbore radius is as follows Figure 7 As shown, there is a good linear relationship between the wellbore radius and the correction coefficient. This correction coefficient equation is used to correct the measurement results for different wellbore radii, and the final lithium content calibration result is obtained, as shown below. Figure 7 As shown, the correction equation can effectively correct the calibration results for different wellbore radii. After correction, the lithium content calibration deviation is less than 5%, which is a good result.

[0096] 2.5 Wellbore water correction

[0097] Because water accumulation in open-pit blast holes can significantly impact logging results, corrections are necessary for water-bearing wells. Hydrogen-captured gamma rays are emitted from the radioactive capture reaction between thermal neutrons and hydrogen, with energy peaks between 2 and 2.4 MeV. The peak energy occurs 10 minutes after the production of a 14 MeV fast neutron. -6 ~10 -3 The hydrogen is generated in seconds. The magnitude of the hydrogen-captured gamma count indicates the concentration within the detector's range. Based on the relative relationship between the hydrogen-captured gamma and the hydrogen content in the wellbore and saturated ore layers, the hydrogen-captured gamma energy spectrum is measured using a gamma detector, and the characteristic peak area of ​​the hydrogen-captured gamma and the wellbore water correction factor μ are calculated. W The response law is used to achieve in-situ correction of well water, with a correction coefficient μ. W The calculation formula is:

[0098]

[0099] Where A N For different water-bearing wells, A represents the area of ​​the characteristic gamma peak of hydrogen capture. B The area of ​​the hydrogen-captured gamma characteristic peak in the dry-pore state is a constant. Finally, based on the relationship between the area of ​​the hydrogen-captured gamma characteristic peak and μ... W Based on the relationship, a correction equation is fitted, and the influence of the characteristic peak of the hydrogen peak in the gamma spectrum of different water-bearing wells on the water-bearing well can be corrected according to the correction equation.

[0100] Simulated gamma spectra of different wellbores under water-bearing conditions, such as Figure 8 As shown, it can be seen that with the increase of the wellbore radius, the time-spectrum decay coefficient of the water increase in the wellbore changes significantly. Figure 9 As can be seen, the area of ​​the hydrogen characteristic peak gradually increases with the increase of water content.

[0101] Based on the above wellbore correction equation and by calculating the hydrogen characteristic peak counts from 2 to 2.4 MeV, a curve showing the relationship between the hydrogen peak counts and the correction coefficient was established, as follows: Figure 9 As shown in (a) of the figure, it can be seen that the H characteristic gamma peak count has a good exponential relationship with the correction coefficient. An equation for the hydrogen characteristic peak count and the correction coefficient is obtained through fitting. Finally, the time spectrum measurement results of different water-bearing wells are corrected based on this correction equation. The results are as follows: Figure 9 As shown in (b) in the figure, the corrected lithium ore grade is within the 5% error range of the true value, and the correction effect is good.

[0102] 2.6 Well Logging Curve Simulation

[0103] Finally, neutron logging models for lithium deposits with different ore layer thicknesses were established. Based on the size of the simulated saturation model, a cylindrical formation model with a height of 16 meters was designed, such as... Figure 10 As shown, the bedrock in layers 1, 3, 5, 7, and 10 from top to bottom is silica bedrock. The minimum thickness of the lithium-bearing layer is 70 cm (layer 4), and the maximum thickness is 2 meters in layer 8. A neutron logging model was moved through the borehole in this formation, measuring a total of 160 points at 10 cm intervals. Neutron time spectra were measured at different locations, and the attenuation coefficients of the time spectra at different locations were fitted using the previously described calculation method. Σ was calculated, and the lithium grade was calculated using a calibration equation and compared with the theoretical value, as shown below. Figure 10 As shown, the calculated results (regional filling and sum) are in good agreement with the theoretical values ​​(curve). However, in the boundary region, the propagation and attenuation characteristics of neutrons in the strata are affected by the surrounding layers. This interference is more significant in thin strata, leading to a decrease in the accuracy of the ore layer boundary measurement results. The simulation results show that the distance of the interlayer influence is approximately 70 cm.

[0104] 3. Conclusion

[0105] This paper proposes a method and apparatus for determining formation lithium grade using pulsed neutron logging technology through the macroscopic cross-section (neutron lifetime) of formation thermal neutron absorption. The measuring apparatus consists of a DT neutron generator, a He3 neutron detector, a lanthanum bromide gamma detector, and corresponding electronic components. The flowchart of the method is shown below. Figure 11As shown. Monte Carlo simulations determined the model size for saturated lithium deposits in the formation: R > 60 cm, H > 140 cm. The neutron time spectrum responses of different lithium grades simulated in the model indicate a linear relationship between lithium grade and nuclear physics parameters (Σ), with the linear calibration equation being: G li =0.0058∙Σ mes -0.0648, R 2 =0.999, and the grade of the formation lithium ore was determined using this degree equation. Corrections were made for the influence of the wellbore radius during logging and for the influence of wellbore water by incorporating gamma spectroscopy information; the relative errors before and after correction were both less than 5%. Finally, a logging case study of a 16m lithium-bearing ore layer was simulated. The comprehensive logging results demonstrate that this wellbore logging method is feasible for in-situ measurement of lithium ore grade, providing a new method for in-situ measurement of lithium ore grade in mine blast holes.

[0106] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for measuring the content of lithium ore in situ through borehole drilling based on pulsed neutron technology, characterized in that, include: Obtain time spectrum information of neutrons detected at the borehole in situ, wherein the time spectrum includes time and corresponding neutron count; The time spectrum information is truncated by a time window; the neutron lifetime is calculated based on the truncated time spectrum information using a time spectrum method. Based on the neutron lifetime, the macroscopic cross-section of the formation under different lithium ore grades is calculated; based on the relationship equation between the macroscopic cross-section of the formation and the lithium content, the calibrated lithium content is calculated based on the macroscopic cross-section of the formation. The lithium content of the scale is located based on the distribution of the macroscopic cross section of the strata, and the scale curve of the lithium content is calculated based on the location results to obtain the actual lithium ore grade distribution of the strata. The equation relating the macroscopic cross section of the formation to the lithium content is as follows: in, The scale indicates the lithium ore content, and K is the scale coefficient. For the measured and calculated macroscopic cross section of the formation, F is the contribution coefficient of the formation skeleton; Before performing calculations based on the aforementioned macroscopic cross-section of the formation, the following steps are also included: Obtain the macroscopic cross section of the formation using the probe, which is the macroscopic cross section of the formation simulated in the wellbore test with the probe radius of the neutron generator; By simulating and establishing a well logging model and a lithium ore formation model, the ratio of different macroscopic cross sections of the formation to the macroscopic cross section of the probe formation is calculated based on the well logging model and the lithium ore formation model, and the correction coefficients for different macroscopic cross sections of the formation are obtained. The macroscopic cross section of the formation is corrected by the corresponding correction factor to obtain the corrected macroscopic cross section for subsequent calculations; After obtaining the time spectrum information, the following is also included: By establishing a well logging model and a lithium ore formation model, the response law of the characteristic peak area of ​​the hydrogen capture gamma spectrum and the well water correction coefficient is calculated based on the well logging model and the lithium ore formation model. A hydrogen-captured gamma spectrum is obtained using a gamma detector. Based on the characteristic peak area of ​​the hydrogen-captured gamma spectrum, the wellbore water correction coefficient is calculated using the response law. The wellbore water correction coefficient is then used to adjust the attenuation coefficient in the time spectrum information, thereby correcting the impact on the water-bearing wellbore.

2. The method according to claim 1, characterized in that, The process of obtaining neutron time spectrum information at the borehole in situ includes: The formation is bombarded by pulsed neutrons emitted by a pulsed neutron generator, and the time spectrum curve of the neutrons, i.e., time spectrum information, is collected by a neutron detector.

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

4. The method according to claim 1, characterized in that, The process of obtaining neutron lifetime includes: in, τ represents the neutron count in the time spectrum information, τ represents the neutron lifetime of the formation, 1 / τ represents the decay coefficient, t represents time, and A represents 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: in, Let τ be the macroscopic cross section of the formation, τ be the neutron lifetime of the formation, and V be the thermal neutron velocity.

6. A borehole in-situ lithium ore content measurement device based on pulsed neutron technology, characterized in that, include: The system includes a pulsed neutron generator, a neutron detector, a gamma detector, and signal processing electronics, wherein the pulsed neutron generator is a deuterium-deuterium or deuterium-tritium pulsed neutron generator, and the neutron detector is... 3 The He neutron detector, pulsed neutron generator, neutron detector, gamma detector and electronic processing equipment are installed inside the probe tube. The neutron detector collects the neutron time spectrum information of the formation bombarded by the pulsed neutron generator. The signal processing electronics are used to perform the borehole in-situ lithium ore content measurement method based on pulsed neutron technology as described in any one of claims 1-5.

7. The apparatus according to claim 6, characterized in that, Also includes: The gamma detector is a lanthanum bromide gamma detector, a sodium iodide gamma detector, a cerium bromide gamma detector, or a bismuth germanate gamma detector. The gamma detector is placed inside the probe tube and is used to measure the hydrogen capture gamma spectrum.

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