Fractured sandstone uranium mine prompt neutron logging numerical simulation method based on dispersed multi-angle random statistical theory

Abstract

The invention relates to a fractured sandstone uranium mine prompt neutron logging numerical simulation method based on a disperse multi-angle random statistical theory. The method comprises the steps of firstly establishing a geological model of the fractured sandstone-containing uranium mine based on a dispersion multi-angle theory; then the simulation pulse neutron source emits neutrons to the stratum, the neutrons and uranium in the cracks are subjected to fission reaction, and instant neutrons are released; then simulating the movement and reaction process of neutrons in the stratum; and finally, recording logging response by a neutron flux counter, and obtaining epithermal neutron count and thermal neutron count according to the energy range. Through tests, the fractured sandstone uranium mine prompt neutron logging numerical simulation method based on the scattered multi-angle random statistical theory can effectively simulate prompt neutron logging responses of sandstone uranium mines under fractures of different angles, and epithermal neutron counting and thermal neutron counting are obtained.

Description

Technical Field

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

[0002] Uranium exploration is of great significance to the development and application of nuclear technology in my country. The widespread fractures in sandstone, due to their unique geological structure, provide excellent storage space and seepage channels for uranium ore development, making them a key target for uranium exploration. Prompt neutron logging is currently a key method in uranium exploration. A pulsed neutron source is used to excite neutrons into the formation, causing them to undergo fission reactions with uranium in the formation fractures, releasing prompt neutrons. Subsequently, as the prompt neutrons diffuse into epithermal and thermal neutrons, the logging response is recorded by a neutron flux counter. However, due to the high production costs of prompt neutron logging and the stringent requirements for instrument operation and data processing, numerical simulation based on geological conditions is essential to provide guidance for actual production. Furthermore, the complex and diverse fracture structures make simulation difficult. Therefore, based on the dispersed multi-angle random statistical theory, this paper studies a prompt neutron logging numerical simulation method for fractured sandstone uranium deposits, which can obtain accurate logging responses according to different geological environments. Through theoretical analysis, it provides guidance methods and suggestions for logging production, instrument development, etc. Summary of the Invention

[0003] The purpose of the present invention is to solve the problems of high cost and strict requirements in actual prompt neutron logging production, and to provide a numerical simulation method for prompt neutron logging in fractured sandstone uranium deposits based on fractional multi-angle random statistical theory.

[0004] The proposed method is suitable for numerical simulation of prompt neutron logging in multi-angle fractured sandstone uranium deposits. The main design principle is as follows: In the numerical simulation, a geological model containing fractured sandstone uranium deposits is first established based on the dispersed multi-angle theory. Then, a pulsed neutron source is simulated to emit neutrons into the formation, where the neutrons undergo fission reactions with uranium in the fractures, releasing prompt neutrons. The neutron movement and reaction process are then simulated. Finally, a neutron flux counter records the logging response, and epithermal and thermal neutron counts are obtained based on the energy range. By analyzing the logging response through numerical simulation, effective guidance and suggestions are provided for the practical application of prompt neutron logging in the exploration of fractured sandstone uranium deposits.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A numerical simulation method for prompt neutron logging in fractured sandstone uranium deposits based on dispersed multi-angle random statistical theory includes the following steps:

[0007] a. Establish a prompt neutron logging model for multi-angle fractured sandstone uranium deposits;

[0008] b. Set the geological environment: The entire underground half-space is assumed to be the matrix, with the matrix medium being a dense rock formation with uniform pore distribution. Fractures are oblong, elliptical structures, evenly and sparsely embedded in the matrix. Several fractures constitute a fracture cluster. The fracture cluster forms the same angle with the well axis, which is the angle formed by the normal direction of the main section of the oblong elliptical structure and the well axis, ranging from 0° to 90°. The fracture number density ranges from 0 to 0.1, and the fracture aspect ratio ranges from 0.0001 to 0.9. Uranium ore is mainly encapsulated in the fractures in the form of pitchblende, with a uranium content ranging from 0.1% to 0.4%. Pyrite particles are attached to the fractures.

[0009] c. Set up the wellbore environment: The well is set to be a vertical well, extending longitudinally, with the wellbore located in the center of the geological model set up in step b. A steel casing is set up in the well, and cement is filled between the outer side of the casing and the wellbore wall to form a cement ring. The outer wall is in close contact with the sandstone uranium ore geological environment. A neutron logging instrument is arranged in the casing in the wellbore, mainly comprising 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. A tungsten-nickel alloy shield is set between the pulsed neutron source and the neutron flux counter;

[0010] d. Pulsed neutron source through reaction Neutrons were emitted into multi-angle fractured sandstone uranium strata, where 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.

[0011] Furthermore, the above method also includes e, neutron Uranium in stratum fissures According to the reaction formula: A fission reaction occurs, in which and For fission fragments, Prompt neutrons are released by fission reactions. Within 0-4000μs after the fission reaction, prompt neutrons slow down into epithermal neutrons and thermal neutrons.

[0012] This process requires accurate simulation and recording of the particle motion process, which can be expressed using the particle state sequence formula S m =(r m ,E m ,Ω m ) indicates that, where r m is the particle position function, E mis the particle energy function, Ω m is the particle migration direction function, and m represents the mth reaction.

[0013] Furthermore, the above method also includes f, particle position function r m Available through r m =r (m-1) + l is determined, where l is the sampling value of the neutron free flight distance, which can be obtained by It is concluded that Σ t is the total macroscopic cross-section of the medium, and ξ is a random number uniformly distributed between (0, 1).

[0014] Furthermore, the above method also includes g. Regarding the determination of the particle energy function, it is necessary to first determine the type of nuclear reaction that occurs with the neutron. The simulated nuclear reaction types are inelastic scattering and elastic scattering. Assume that the microscopic cross sections of the nuclides in the formation are σ in ,σ el , the total microscopic cross section is σ t , the nuclear reaction type is determined by discrete random variable sampling method, that is,

[0015] Furthermore, the above method also includes h, determining the particle energy function E m , when inelastic scattering occurs, in

[0016] When elastic scattering occurs, Where A is the mass of the colliding nucleus, θ C is the scattering angle in the mass center coordinate system, μ C =cosθ C , ε K and γ K are the threshold energy and excitation energy of the Kth level respectively.

[0017] Furthermore, the above method further includes i. determining the particle migration direction function Ω m , let θ L is the scattering angle of the laboratory coordinate system, λ is the azimuth angle uniformly distributed on (0, 1), let a = cosθ L , b=sinθ L , c=cosλ, d=sinλ, then Ω m Cosine u in three dimensions m , v m and w m They are:

[0018]

[0019] Finally, the above method also includes j, simulating a neutron flux counter with a point flux to record the result, i.e., the logging response, and assuming that the particle state after the nth reaction is S n =(r n ,E n ,Ω n ), then for point r * The flux count is Where δ(·) represents the Dirac function, W n is the weight of the particle after n reactions, Σ t and l can be defined and calculated by f steps, so the total count of the neutron flux counter during the entire reaction is Among them, those with energy less than 1eV are epithermal neutrons, and those with energy between 0.7eV and 1keV are thermal neutrons. The above steps complete the numerical simulation of the prompt neutron logging response of fractured sandstone uranium deposits.

[0020] The beneficial effects of the present invention are as follows: through experiments, the numerical simulation method of prompt neutron logging of fractured sandstone uranium deposits based on fractional multi-angle random statistical theory disclosed by the present invention can effectively simulate the prompt neutron logging response of sandstone uranium deposits under fractures of different angles, obtain epithermal neutron counts and thermal neutron counts, and further analyze the uranium content, providing effective guidance methods and suggestions for the practical application of prompt neutron logging for uranium mine exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the geological model of the fractured sandstone uranium deposit and the wellbore environment model diagram established for the present invention.

[0022] Figure 2 This is the epithermal neutron count distribution at a slit angle of 20°.

[0023] Figure 3 This is the thermal neutron count distribution at a crack angle of 20°.

[0024] Figure 4 This is the epithermal neutron count distribution at a 50° crack angle.

[0025] Figure 5 This is the thermal neutron count distribution at a crack angle of 50°.

[0026] Figure 6 This is the epithermal neutron count distribution at a crack angle of 80°.

[0027] Figure 7 This is the thermal neutron count distribution at a crack angle of 80°. DETAILED DESCRIPTION

[0028] like Figures 1 to 7As shown in FIG, the numerical simulation method of prompt neutron logging in fractured sandstone uranium deposits based on fractional multi-angle random statistical theory includes the following sequence and steps:

[0029] a. Establish a prompt neutron logging model for multi-angle fractured sandstone uranium deposits;

[0030] b. Set the geological environment: Set the underground half space of 100 meters long, 100 meters wide and 500 meters deep as the matrix, and the matrix medium is a dense rock layer with uniform pore distribution. Several oblong elliptical structural cracks are evenly and sparsely embedded in the matrix to form a crack group. The crack group is at the same angle as the well axis, which is the angle formed by the normal direction of the oblong elliptical main section and the well axis, which is 40°. The crack number density is 0.1, and the crack aspect ratio is 0.5. Uranium ore is mainly wrapped in the cracks in the form of pitchblende, and the uranium content ranges from 0.2. Pyrite particles are attached around the cracks;

[0031] c. Set the wellbore environment: Set the well as a vertical well, extending longitudinally, with a borehole diameter of 25 cm, located in the center of the geological model set in step b. Set a steel casing in the well, with an outer diameter of 18 cm and a thickness of 6 cm. Fill the space between the outer side of the casing and the well wall with cement to form a cement ring, and the outer wall of the cement ring is close to the geological environment. Arrange a deuterium-tritium pulsed neutron source, a thermal neutron detector and an epithermal neutron detector in the casing of the well. At the same time, set a tungsten-nickel alloy shield between the pulsed neutron source and the neutron detector. The entire simulation environment is as follows: Figure 1 As shown, the wellbore environment, geological model and instrument location are noted, with special attention to the definition of fracture angle;

[0032] d. Pulsed neutron source through reaction Neutrons were emitted into the multi-angle fractured sandstone uranium strata with an emission interval of 3×10 -6 seconds, and the total number of particles emitted is 1×10 8 Among them, It is a neutron emitted with an energy of 17MeV;

[0033] e. Further, the emitted neutrons Uranium in stratum fissures According to the reaction formula: A fission reaction occurs. and For fission fragments, is the prompt neutron released by the fission reaction. Within 0-4000μs after the fission reaction, the prompt neutron slows down to epithermal neutrons and thermal neutrons. m =(r m ,E m ,Ω m ) simulates the particle state, where r m is the particle position function, Em is the particle energy function, Ω m is the particle migration direction function, m represents the mth reaction;

[0034] f, particle position function r m Available through r m =r (m-1) + l is determined. Where l is the sampling value of the neutron free flight distance, which can be obtained by Σ t is the total macroscopic cross-section of the medium, ξ is a random number uniformly distributed between (0, 1);

[0035] g. To determine the particle energy function, we must first determine the type of nuclear reaction that occurs with neutrons. The nuclear reaction types simulated in this invention are inelastic scattering and elastic scattering. Assume that the microscopic cross sections of the nuclides in the formation are σ in ,σ el , the total microscopic cross section is σ t , the nuclear reaction type is determined by discrete random variable sampling method, that is,

[0036]

[0037] h. Further, determine the particle energy function. When inelastic scattering occurs, in When elastic scattering occurs, Where A is the mass of the colliding nucleus, θ C is the scattering angle in the mass center coordinate system, μ C =cosθ C , ε K and γ K are the threshold energy and excitation energy of the Kth level respectively;

[0038] i. Further, determine the particle migration direction function Ω m Let θ L is the scattering angle of the laboratory coordinate system, λ is the azimuth angle uniformly distributed on (0, 1), let a = cosθ L , b=sinθ L , c=cosλ, d=sinλ, then Ω m Cosine u in three dimensions m , v m and w m They are:

[0039]

[0040] j. Finally, the neutron flux counter is used to simulate the logging response using point flux. Assume that the particle state after the nth reaction is S n =(r n ,En ,Ω n ), then for point r * The flux count is Where δ(·) represents the Dirac function, W n is the weight of the particle after n reactions, Σ t and l can be defined and calculated by step f. Therefore, the total count of the neutron flux counter during the entire reaction is Among them, those with energy less than 1eV are epithermal neutrons, and those with energy between 0.7eV and 1keV are thermal neutrons. Figures 2 to 7 , respectively showing the prompt neutron logging responses at different fracture angles, namely, epithermal neutron counts and thermal neutron counts. The above steps complete the numerical simulation of the prompt neutron logging response of fractured sandstone uranium deposits.

[0041] Experiments have shown that the present invention discloses a numerical simulation method for prompt neutron logging of fractured sandstone uranium deposits based on dispersed multi-angle random statistical theory, which can effectively simulate the prompt neutron logging response of sandstone uranium deposits under fractures of different angles, obtain epithermal neutron counts and thermal neutron counts, and can further perform data processing to analyze uranium content. It can also optimize the design of various parameters of the pulsed neutron source, providing effective guidance methods and suggestions for the practical application of prompt neutron logging in uranium mine exploration.

[0042] 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 numerical simulation method for prompt neutron logging in fractured sandstone uranium deposits based on dispersed multi-angle random statistical theory, characterized in that: The following steps are involved: a. Establish a prompt neutron logging model for multi-angle fractured sandstone uranium deposits; b. Set the geological environment: The entire underground half-space is assumed to be the matrix, with the matrix medium being a dense rock formation with uniform pore distribution. Fractures are oblong, elliptical structures, evenly and sparsely embedded in the matrix. Several fractures constitute a fracture cluster. The fracture cluster forms the same angle with the well axis, which is the angle formed by the normal direction of the main section of the oblong elliptical structure and the well axis, ranging from 0° to 90°. The fracture number density ranges from 0 to 0.1, and the fracture aspect ratio ranges from 0.0001 to 0.

9. Uranium ore is mainly encapsulated in the fractures in the form of pitchblende, with a uranium content ranging from 0.1% to 0.4%. Pyrite particles are attached to the fractures. c. Set up the wellbore environment: The well is set to be a vertical well, extending longitudinally, with the wellbore located in the center of the geological model set up in step b. A steel casing is set up in the well, and cement is filled between the outer side of the casing and the wellbore wall to form a cement ring. The outer wall is in close contact with the sandstone uranium ore geological environment. A neutron logging instrument is arranged in the casing in the wellbore, mainly comprising 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. A tungsten-nickel alloy shield is set between the pulsed neutron source and the neutron flux counter; d. Pulsed neutron source through reaction Neutrons were emitted into multi-angle fractured sandstone uranium strata, where 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 numerical simulation of prompt neutron logging in fractured sandstone uranium deposits based on dispersed multi-angle random statistical theory according to claim 1 is characterized in that: Also includes e, neutron Uranium in stratum fissures According to the reaction formula: A fission reaction occurs, in which and For fission fragments, Prompt neutrons are released by fission reactions. Within 0-4000μs after the fission reaction, prompt neutrons slow down into epithermal neutrons and thermal neutrons. This process requires accurate simulation and recording of the particle motion process, which can be expressed using the particle state sequence formula S m =(r m ,E m ,Ω m ) indicates that, where r m is the particle position function, E m is the particle energy function, Ω m is the particle migration direction function, and m represents the mth reaction.

3. The method for numerical simulation of prompt neutron logging in fractured sandstone uranium deposits based on dispersed multi-angle random statistical theory according to claim 2, characterized in that: Also includes f, particle position function r m Available through r m =r (m-1) + l is determined, where l is the sampling value of the neutron free flight distance, which can be obtained by It is concluded that Σ t is the total macroscopic cross-section of the medium, and ξ is a random number uniformly distributed between (0, 1).

4. The method for numerical simulation of prompt neutron logging in fractured sandstone uranium deposits based on dispersed multi-angle random statistical theory according to claim 2, characterized in that: Regarding the determination of the particle energy function, it is necessary to first determine the type of nuclear reaction that occurs with neutrons. The simulated nuclear reaction types are inelastic scattering and elastic scattering. Assume that the microscopic cross sections of the nuclides in the formation are σ in ,σ el , the total microscopic cross section is σ t , the nuclear reaction type is determined by discrete random variable sampling method, that is, Determine the particle energy function when inelastic scattering occurs. in When elastic scattering occurs, Where A is the mass of the colliding nucleus, θ C is the scattering angle in the mass center coordinate system, μ C =cosθ C , ε K and γ K are the threshold energy and excitation energy of the Kth level respectively.

5. The method for numerical simulation of prompt neutron logging in fractured sandstone uranium deposits based on dispersed multi-angle random statistical theory according to claim 2, characterized in that: Determine the particle migration direction function Ω m , let θ L is the scattering angle of the laboratory coordinate system, λ is the azimuth angle uniformly distributed on (0, 1), let a = cosθ L , b=sinθ L , c=cosλ, d=sinλ, then Ω m Cosine u in three dimensions m , v m and w m They are:

6. The method for numerical simulation of prompt neutron logging in fractured sandstone uranium deposits based on dispersed multi-angle random statistical theory according to claim 2, characterized in that: Finally, the neutron flux counter is simulated with point flux to record the results, i.e. the logging response. The particle state after the nth reaction is S n =(r n ,E n ,Ω n ), then for point r * The flux count is Where δ(·) represents the Dirac function, W n is the weight of the particle after n reactions, Σ t and l can be defined and calculated by f steps, so the total count of the neutron flux counter during the entire reaction is Among them, those with energy less than 1eV are epithermal neutrons, and those with energy between 0.7eV and 1keV are thermal neutrons. The above steps complete the numerical simulation of the prompt neutron logging response of fractured sandstone uranium deposits.

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