Method for measuring uranium content of multi-angle fractured sandstone uranium mine based on prompt neutron logging

Abstract

The invention discloses a method for measuring the uranium content of a multi-angle fractured sandstone uranium mine based on prompt neutron logging. The method comprises the following steps: firstly, establishing an instantaneous neutron logging model of the fractured sandstone uranium mine based on a Husdon fracture theory; then different fracture angles are set, and epithermal neutron counting and thermal neutron counting are obtained through simulation. According to the theory that the ratio of the epithermal neutrons to the thermal neutrons is in linear relation with the uranium content, numerical fitting is conducted on the curve of the ratio of the epithermal neutrons to the thermal neutrons and the uranium content through an exponential function, and the correction relation between the ratio of the epithermal neutrons to the thermal neutrons and the uranium content at different fracture angles is obtained. And finally substituting into an actual measurement result to obtain a more accurate uranium content. Through tests, the method for measuring the uranium content of the multi-angle fracture type sandstone uranium mine based on prompt neutron logging can effectively simulate prompt neutron logging response under fractures of different angles, and correct the linear relation between the ratio of epithermal neutrons to thermal neutrons and the uranium content, so that the more accurate uranium content is obtained.

Description

Technical Field

[0001] The present invention relates to the fields of geophysical exploration and nuclear technology application, and in particular to a method for measuring uranium content in multi-angle fractured sandstone uranium deposits based on prompt neutron logging. Background Art

[0002] Uranium is a crucial raw material in nuclear technology, and accurately measuring the uranium content in uranium ore is crucial for my country's energy security. The widespread fractures in sandstone, due to their unique geological structure, are important reservoirs for uranium deposits and a key target for nuclear logging exploration. Currently, prompt neutron logging is a common method used in uranium exploration. Neutrons are excited by a neutron source, causing fission reactions between the neutrons and uranium in the formation, releasing prompt neutrons. During the diffusion of prompt neutrons, a neutron flux counter measures epithermal and thermal neutron counts. The uranium content is calculated based on the theory that the ratio of the epithermal to thermal neutron counts is linearly related to the uranium content. However, the presence of fractures, particularly those at different angles, significantly affects the radiation angle between particles and uranium minerals in the fracture inclusions, the number of reactive nuclei, and the types of reactive nuclei, thus affecting the accuracy of uranium content measurements. Therefore, the present invention studies a method for measuring the uranium content in multi-angle fractured sandstone uranium deposits. By correcting the theoretical linear relationship through numerical simulation, the present invention provides an effective guidance method for the practical application of prompt neutron logging in fractured uranium deposit exploration and quantitative analysis of uranium content. Summary of the Invention

[0003] The purpose of the present invention is to solve the defects of the prior art and provide a method for measuring the uranium content in multi-angle fractured sandstone uranium deposits based on prompt neutron logging.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A method for measuring uranium content in multi-angle fractured sandstone uranium deposits based on prompt neutron logging comprises the following steps:

[0006] a. Establish a prompt neutron logging model for sandstone uranium deposits containing multi-angle fractures;

[0007] b. Simulate the geological environment according to the following requirements: Set the underground half-space as a fractured sandstone uranium mining area, and the matrix as a uniformly distributed dense sandstone layer. Build a fracture model based on Hudson theory, and the fractures are elliptical coin-shaped and evenly and sparsely distributed throughout the matrix.

[0008] The fracture angle θ is defined as the angle between the normal of the long diagonal of the ellipse and the vertical well axis. The simulation is consistent with the actual situation. All fracture angles are the same. Uranium ore is present in the fractures in the form of pitchblende, with a uranium content ranging from 0.1% to 0.4%. Pyrite mineral particles are wrapped around the fractures.

[0009] c. Simulate the wellbore environment according to the following requirements: the well is a vertical well, the wellbore is located in the center of the geological model set in step b, the wellbore diameter is 20 cm, the wellbore is provided with a casing with an outer diameter of 16 cm and a thickness of 5 mm, made of steel, and a cement sheath with a thickness of 4 cm, mainly made of CaSiO3, between the casing and the wellbore wall, with the outer wall of the cement sheath closely adhering to the sandstone uranium geology environment;

[0010] d. Simulate the logging instrument according to the following requirements: Place a neutron logging instrument in the well casing, which mainly includes a pulsed neutron source and a neutron flux counter; the pulsed neutron source is a deuterium-tritium neutron source, and the neutron flux counter includes a thermal neutron detector and an epithermal neutron detector, both of which are 3 H e The gas detector works synchronously with the pulsed neutron source. A shield is set between the pulsed neutron source and the neutron flux counter, and is mainly made of tungsten-nickel alloy.

[0011] e. Pulsed neutron source according to the reaction formula Neutrons are emitted into multi-angle sandstone uranium strata, among which, It is tritium, which contains 1 proton and 2 neutrons; It is deuterium, which contains 1 proton and 1 neutron; It is helium, which contains 2 protons and 4 neutrons. It is a neutron emitted with an energy of 17MeV.

[0012] Furthermore, the above method further comprises: emitting neutrons to the formation Uranium in the stratum fissures According to the reaction formula: A fission reaction occurs, in which and For fission fragments, Prompt neutrons are generated by fission reactions. Within 0-4000μs after the fission reaction, prompt neutrons slow down into epithermal neutrons and thermal neutrons. During this process, the epithermal neutron count N with energy less than 1eV is recorded by the epithermal neutron detector. ep (t), the thermal neutron detector records the number of thermal neutrons N with energy between 0.7 eV and 1 keV th (t).

[0013] Furthermore, the above method also includes g: In theory, the ratio of epithermal neutron count to thermal neutron count is linearly related to the uranium content, that is: Among them, P v is the uranium content in the formation, if Then the linear relationship can be simplified to in, α, A respectively U 235 The abundance and atomic weight of N A is Avogadro's constant, σ f For thermal neutrons and U 235 The fission cross section between ν and ν is the average yield of prompt neutrons released by the fission reaction;

[0014] Furthermore, the above method also includes h: Since cracks of different angles will significantly affect the radiation angle, number of reactive nuclei, and reaction type between particles and uranium minerals in crack inclusions, the coefficient k in the above linear relationship will vary with the crack angle. Therefore, the crack angle θ is set from 0°, with increments of 10° up to 90°, and steps bg are repeated to obtain the ratio of epithermal neutron counts to thermal neutron counts at different crack angles.

[0015] Furthermore, the above method further comprises: i. firstly, at each crack angle, the uranium content P v The horizontal axis is the ratio of epithermal neutron count to thermal neutron count. As the vertical coordinate, the uranium content correction curve is obtained, and then the exponential function is applied to numerically fit the curve to obtain the correction coefficient k' at the crack angle. Finally, the linear relationship formula of step g is corrected to obtain the accurate uranium content at the crack angle.

[0016] Furthermore, the above method also includes j: in actual production, the fracture angle and sandstone matrix parameters of the region are obtained according to the geological survey, and then combined with the instrument parameters, numerical simulation is performed according to the above steps ai to obtain the correction coefficient k', and then the epithermal neutron count N is obtained according to the neutron flux counter measurement. ep (t) and thermal neutron count value N th (t), and finally into the correction formula A more accurate uranium content can be obtained, and then quantitative analysis of multi-angle fractured sandstone uranium deposits can be carried out.

[0017] The beneficial effects of the present invention are as follows: the method for measuring uranium content in multi-angle fractured sandstone uranium deposits based on prompt neutron logging provided by the present invention can effectively simulate the prompt neutron logging response under fractures of different angles, thereby correcting the linear relationship between the ratio of epithermal neutron counts to thermal neutron counts and uranium content, and ultimately providing an effective guidance method for the practical application of prompt neutron logging for uranium mine exploration and quantitative analysis of uranium content. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1This is a geological model diagram of a 50° fracture-type sandstone uranium deposit established based on Hundson's fracture theory in the present invention.

[0019] Figure 2 This is the relationship curve between the ratio of epithermal neutron counts to thermal neutron counts and uranium content under low-angle cracks.

[0020] Figure 3 This is a graph showing the relationship between the ratio of epithermal neutron counts to thermal neutron counts and uranium content under medium-angle cracks.

[0021] Figure 4 This is a graph showing the relationship between the ratio of epithermal neutron counts to thermal neutron counts and uranium content under high-angle cracks.

[0022] Figure 5 The figure shows the correction relationship curve and change trend diagram under different crack angles. DETAILED DESCRIPTION

[0023] like Figures 1 to 5 As shown, a method for measuring uranium content in multi-angle fractured sandstone uranium deposits based on prompt neutron logging includes the following sequence and steps:

[0024] a. Establish a prompt neutron logging model for sandstone uranium deposits containing multi-angle fractures;

[0025] b. Set up an underground half-space 100 meters long, 100 meters wide, and 500 meters deep as a fractured sandstone uranium mining area. The matrix is ​​a uniformly distributed dense sandstone layer, with the following main components and contents: Based on the Hudson theory, elliptical coin-shaped fractures are established, evenly and sparsely distributed throughout the matrix. To be consistent with the actual situation, all fractures in the simulation have the same angle, which is the angle between the normal of the long diagonal of the ellipse and the vertical well axis. Uranium ore occurs in the fractures in the form of pitchblende, with a uranium content ranging from 0.1% to 0.4%. Pyrite mineral particles surround the fractures;

[0026] c. A 20-cm diameter wellbore was set in the center of the geological model. A vertical wellbore was installed with a 16-cm outer diameter, 5-mm thick steel casing. A 4-cm thick cement sheath, primarily made of CaSiO₃, was placed between the casing and the wellbore wall. The outer wall of the cement sheath adhered closely to the sandstone uranium deposit's geological environment.

[0027] d. Set up a pulsed neutron source and a neutron flux counter in the well casing. The pulsed neutron source is a deuterium-tritium neutron source, and the neutron flux counter includes a thermal neutron detector and an epithermal neutron detector, both of which are 3 H e The gas detector works synchronously with the pulsed neutron source and a shield is set between the pulsed neutron source and the neutron flux counter, which is mainly made of tungsten-nickel alloy. The entire simulation environment set up by the ad step is as follows Figure 1 As shown, the wellbore environment, geological environment and instruments are indicated in the figure, especially the definition of the fracture angle is marked;

[0028] e. Pulsed neutron source according to the reaction formula Neutrons are emitted to multi-angle sandstone uranium strata. It is a neutron emitted with an energy of 17MeV;

[0029] f. Further, neutrons emitted into the formation Uranium in the stratum fissures According to the reaction formula: A fission reaction occurs. Prompt neutrons are generated by fission reactions. Within 0-4000μs after the fission reaction, prompt neutrons slow down to epithermal neutrons and thermal neutrons. During this process, the epithermal neutron detector records the number of epithermal neutrons with energy less than 1eV. ep (t), the thermal neutron detector records the number of thermal neutrons N with energy between 0.7 eV and 1 keV th (t);

[0030] g. Theoretically, the ratio of epithermal neutron count to thermal neutron count is linearly related to the uranium content, that is: Among them, P v is the uranium content in the formation, Then the linear relationship formula can be simplified to in, A respectively U 235 The abundance and atomic weight of N A is Avogadro's constant, σ f For thermal neutrons and U 235 The fission cross section between ν and ν is the average yield of prompt neutrons released by the fission reaction;

[0031] However, since cracks of different angles significantly affect the radiation angles of particles and uranium minerals in the crack inclusions, the number of reactive nuclei, and the types of reactive nuclei, the coefficient k in the above linear relationship will vary with the crack angle. Therefore, the crack angle θ is set from 0° to 90°, with an increment of 10°, and steps bg are repeated to obtain the ratio of epithermal neutron counts to thermal neutron counts at different crack angles, as shown in the figure. Figure 2 、 Figure 3 、 Figure 4 As shown;

[0032] i. Specifically, at each crack angle, firstly, the uranium content P v The horizontal axis is set to 0.1%-0.4% according to the simulation, with the ratio of epithermal neutrons to thermal neutrons. As the vertical coordinate, the uranium content correction curve is obtained. Then the exponential function is applied to the curve to numerically fit and the correction coefficient k' is obtained under the crack angle. Finally, the linear relationship formula of step g is corrected to obtain that when the low angle crack is 0°-30°, When the angle of the crack is 40°-60°, When the high angle crack is 70°-90°, With the crack angle as the horizontal axis and the correction coefficient k', the curve trend is as follows Figure 5 As shown;

[0033] j. In actual operation, first obtain the fracture angle and sandstone matrix parameters of the area according to the geological survey, then combine the instrument parameters and perform numerical simulation according to the above steps to obtain the correction coefficient k'. Finally, according to the ratio of the epithermal neutron count and thermal neutron count value measured by the neutron flux counter, combined with the correction coefficient k', Get a more accurate uranium content p v ', and then quantitatively analyze multi-angle fractured sandstone uranium deposits, providing guidance for the practical application of prompt neutron logging in uranium exploration.

[0034] Experiments have shown that the method for measuring uranium content in multi-angle fractured sandstone uranium deposits based on prompt neutron logging disclosed in the present invention can effectively simulate the prompt neutron logging response and correct the linear relationship between the ratio of epithermal neutron counts to thermal neutron counts and uranium content, providing an effective guidance method for accurately measuring uranium content.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring uranium content in multi-angle fractured sandstone uranium deposits based on prompt neutron logging, characterized in that: The following steps are involved: a. Establish a prompt neutron logging model for sandstone uranium deposits containing multi-angle fractures; b. Simulate the geological environment according to the following requirements: Set the underground half-space as a fractured sandstone uranium mining area, and the matrix as a uniformly distributed dense sandstone layer. Build a fracture model based on Hudson theory, and the fractures are elliptical coin-shaped and evenly and sparsely distributed throughout the matrix. The fracture angle θ is defined as the angle between the normal of the long diagonal of the ellipse and the vertical well axis. The simulation is consistent with the actual situation. All fracture angles are the same. Uranium ore is present in the fractures in the form of pitchblende, with a uranium content ranging from 0.1% to 0.4%. Pyrite mineral particles are wrapped around the fractures. c. Simulate the wellbore environment according to the following requirements: the well is a vertical well, the wellbore is located in the center of the geological model set in step b, the wellbore diameter is 20 cm, the wellbore is provided with a casing with an outer diameter of 16 cm and a thickness of 5 mm, made of steel, and a cement sheath with a thickness of 4 cm, mainly made of CaSiO3, between the casing and the wellbore wall, with the outer wall of the cement sheath closely adhering to the sandstone uranium geology environment; d. Simulate the logging instrument according to the following requirements: Place a neutron logging instrument in the casing of the well, which mainly includes a pulsed neutron source and a neutron flux counter; the pulsed neutron source is a deuterium-tritium neutron source, and the neutron flux counter includes a thermal neutron detector and an epithermal neutron detector, both of which are 3 H e The gas detector works synchronously with the pulsed neutron source. A shield is set between the pulsed neutron source and the neutron flux counter, and is mainly made of tungsten-nickel alloy. e. Pulsed neutron source according to the reaction formula Neutrons are emitted into multi-angle sandstone uranium strata, among which, It is tritium, which contains 1 proton and 2 neutrons; It is deuterium, which contains 1 proton and 1 neutron; It is helium, which contains 2 protons and 4 neutrons. It is a neutron emitted with an energy of 17MeV.

2. The method for measuring uranium content in multi-angle fractured sandstone uranium deposits based on prompt neutron logging according to claim 1, characterized in that: Also includes f: neutrons emitted to the formation Uranium in the stratum fissures According to the reaction formula: A fission reaction occurs, in which and For fission fragments, Prompt neutrons are generated by fission reactions. Within 0-4000μs after the fission reaction, prompt neutrons slow down into epithermal neutrons and thermal neutrons. During this process, the epithermal neutron count N with energy less than 1eV is recorded by the epithermal neutron detector. ep (t), the thermal neutron detector records the number of thermal neutrons N with energy between 0.7 eV and 1 keV th (t).

3. The method for measuring uranium content in multi-angle fractured sandstone uranium deposits based on prompt neutron logging according to claim 2, characterized in that: Also includes g: Theoretically, the ratio of epithermal neutron count to thermal neutron count is linearly related to the uranium content, that is: Among them, P v is the uranium content in the formation, if Then the linear relationship can be simplified to in, α, A respectively U 235 The abundance and atomic weight of N A is Avogadro's constant, σ f For thermal neutrons and U 235 The fission cross section between ν and ν is the average yield of prompt neutrons released by the fission reaction.

4. The method for measuring uranium content in multi-angle fractured sandstone uranium deposits based on prompt neutron logging according to claim 3, characterized in that: Also included is h: Since cracks of different angles will significantly affect the radiation angle between particles and uranium minerals in crack inclusions, the number of reactive nuclei, and the type of reactive species, the coefficient k in the above linear relationship will vary with the crack angle. Therefore, the crack angle θ is set from 0°, incremented by 10° to 90°, and steps bg are repeated to obtain the ratio of epithermal neutron counts to thermal neutron counts at different crack angles.

5. The method for measuring uranium content in multi-angle fractured sandstone uranium deposits based on prompt neutron logging according to claim 3, characterized in that: Also includes i: at each crack angle, first the uranium content P v The horizontal axis is the ratio of epithermal neutron count to thermal neutron count. As the vertical coordinate, the uranium content correction curve is obtained, and then the exponential function is applied to numerically fit the curve to obtain the correction coefficient k' at the crack angle. Finally, the linear relationship formula of step g is corrected to obtain the accurate uranium content at the crack angle.

6. The method for measuring uranium content in multi-angle fractured sandstone uranium deposits based on prompt neutron logging according to claim 5, characterized in that: It also includes j: In actual production, the fracture angle and sandstone matrix parameters of the area are obtained according to the geological survey, and then combined with the instrument parameters, numerical simulation is performed according to the above steps ai to obtain the correction coefficient k', and then the epithermal neutron count N is obtained according to the neutron flux counter measurement. ep (t) and thermal neutron count value N th (t), and finally into the correction formula A more accurate uranium content can be obtained, and then quantitative analysis of multi-angle fractured sandstone uranium deposits can be carried out.

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