Method and device for preparing dense uranium-containing sandstone artificial core

Abstract

The present invention discloses a method for preparing a dense uranium-bearing sandstone artificial core. The method comprises mixing quartz sand and feldspar of different particle sizes, adding clay, uranium-bearing minerals, and calcium hydroxide powder, and mixing. The mixture is then sprayed with water to moisten the mixture, stirred, and cooled to room temperature. The mixture is placed in a core mold and heated and pressurized, while simultaneously injecting a small amount of preheated water to maintain a constant temperature and pressure for reaction. Carbon dioxide and hydrogen sulfide gases are introduced into the core mold at least three times, and the amount of gas and liquid that do not participate in the reaction is collected and measured. The mold is then cooled and depressurized, followed by drying, and the amount of gas and liquid that participate in the reaction is measured. The reaction pressure, temperature, and pH are evaluated, and the pressure, temperature, and gas and liquid injection rates are adjusted until a sample similar to the diagenetic environment of natural dense uranium-bearing sandstone is obtained. The method can realistically simulate the hydrothermal fluid injection process, as well as the sedimentation, compaction, cementation, replacement, and dissolution diagenesis processes involved in the diagenetic process of uranium-bearing sandstone, thereby producing a dense uranium-bearing sandstone artificial core with satisfactory physical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of uranium mine exploration and development, and in particular to a method and device for preparing dense uranium-containing sandstone artificial cores. Background Art

[0002] Nuclear energy, as a stable, clean energy source, offers the advantages of being green, low-carbon, providing a stable power supply, and possessing high energy density. Uranium resources, as a key raw material for nuclear power development, play a crucial role in energy resource security. Currently, sandstone uranium deposits, as the primary type of uranium resource, are gaining increasing attention. Artificial core physical simulation is a crucial tool for solving scientific research tasks during uranium resource exploration and development, requiring a large number of cores throughout the research process.

[0003] Sandstone-type uranium deposits are often characterized by deep burial depth, low permeability, dense porosity, and a high degree of reservoir cementation. Conventional drilling and coring methods are costly and inefficient, making it difficult to study the occurrence of uranium ore within the reservoir, its pore structure, permeability evolution, and fluid flow mechanisms. Therefore, the development of artificial dense uranium-bearing sandstone is imperative to provide experimental support for uranium exploration and development technology research. Furthermore, in situ leaching of uranium from sandstone-type uranium deposits has become the predominant method for natural uranium production both domestically and internationally. Using reproducible artificial cores to study changes in reservoir micropore structure and inversely simulate the seepage process of the leachate during in situ leaching can provide technical support for improving uranium leaching efficiency.

[0004] Chinese patent CN107144452A discloses a method for preparing a shallow loose oil-bearing artificial sandstone core of the Guantao Formation. The method grinds the loose sandstone of the target layer into powder with a ball mill, then sieves out sand samples of different particle sizes with a standard test sieve, then weighs the sand samples of different particle sizes and mixes them evenly, then mixes the mixed sand sample, adds a binder of acetone, and emulsified oil and stirs until there are no larger particles, then puts it into a core preparation mold, and applies pressure and presses it into shape by a hydraulic jack, finally seals it with tinfoil and places it in a cool place to air dry, thereby obtaining an oil-bearing artificial sandstone core. This method is simple in process, low in cost, and has a pore structure close to that of a natural core. However, this method does not undergo the diagenetic process of high temperature and cementation, and the addition of multiple chemical substances causes the composition difference from the real rock sample to be too large.

[0005] Chinese patent CN104931312A discloses a temperature-pressure dual-control dense artificial sandstone core and its preparation method. The method mixes 100g-200g of quartz sand with a particle size of 300-500 mesh in 100mL-150mL of water, and heats it to 300℃-350℃, increases the pressure to 220MPa-250MPa, reacts at constant temperature and pressure for 15h-20h, cools and reduces the pressure to room temperature and atmospheric pressure, and takes out the sample to obtain a temperature-pressure dual-control dense artificial sandstone core. The core prepared by this invention has an overall pore structure that is highly similar to the pore structure of real geological samples. However, the composition of the core prepared by this method is different from that of real sandstone, and there are problems of high cost and long production cycle.

[0006] Chinese patent CN103880384A discloses an artificial sandstone core, preparation method, and use. The core is prepared primarily from the following raw materials, based on the weight percentage of each component: 220% clay, 5-25% cement, 0-10% feldspar (excluding 0), and 70-95% quartz sand. This method boasts a simple structure and stable performance, effectively overcoming the significant differences between artificial cores and natural cores in pore throat distribution and wettability. However, the artificial cores produced by this method do not undergo the diagenetic process of compaction followed by cementation, significantly differing from the diagenetic process of authentic samples. Furthermore, the addition of multiple chemical substances results in poor inertness, complex composition, and unstable core properties.

[0007] Chinese patent CN112924260A discloses a calcareous cemented artificial rock core and its preparation and application, comprising the following steps: 1) mixing quartz sand of varying particle sizes; 2) moistening the quartz sand with water, then adding calcium hydroxide powder to the mixture to obtain a mixture of quartz sand, water, and calcium hydroxide; 3) adding the mixture to a core mold and compacting it under pressure to obtain a compacted sample; 4) placing the compacted sample into a reactor, introducing carbon dioxide gas to react, and then drying it. This reaction is repeated at least once to obtain a reacted sample; and 5) drying the reacted sample to obtain a calcareous cemented artificial rock core. This method can realistically simulate the compaction and cementation processes during rock diagenesis and meet the requirements for rock physical and chemical characterization testing. However, this method only uses quartz sand and calcium hydroxide powder as experimental raw materials and cannot obtain real-time information on the temperature, pressure, and pH of the rock sample during the reaction, nor the final gas-liquid content involved in the reaction. Therefore, it is difficult to approximate the actual core composition to a certain extent.

[0008] In summary, although predecessors have conducted extensive research on the production of artificial sandstone cores, the existing artificial core preparation technology still has the following problems: 1. The equipment for preparing artificial cores is too simple, such as using only a hydraulic jack to apply pressure and press into shape, or it is too complicated or expensive, such as using a high-temperature and high-pressure reactor; 2. The artificial cores produced do not undergo the diagenetic process of first compaction and then cementation, which is quite different from the diagenetic process of real samples. In addition, a variety of chemical substances are added, resulting in poor inertness, too complex components, and unstable core properties; 3. The production process of artificial cores is inconsistent with the composition, pore throat structure and mechanical properties of natural cores, which limits the research and development of uranium resource exploration and development technology. Summary of the Invention

[0009] The main purpose of this invention is to provide a method for preparing dense uranium-containing sandstone artificial cores. This method has the advantages of simple production process and low economic cost. The resulting artificial uranium-containing cores have stable properties and diverse composition. Their diagenesis, pore throat structure, and mechanical properties are closer to those of natural cores. This method can provide reliable support for the simulation of fluid flow mechanisms within dense sandstone-type uranium reservoirs and the inversion of in-situ leaching mining processes. A corresponding device for implementing this preparation method is also proposed.

[0010] The technical solution adopted in the present invention is:

[0011] A method for preparing a dense uranium-containing sandstone artificial core comprises the following steps:

[0012] S1. After mixing quartz sand and feldspar of different particle sizes, clay, uranium-containing minerals and calcium hydroxide powder are added and mixed thoroughly;

[0013] S2. Spray water on the mixed system obtained in S1 to moisten it, to obtain a mixed system of water, quartz sand, feldspar, clay, uranium-containing mineral, and calcium hydroxide. After stirring, cool to room temperature, and measure the total weight. Then, the residual water content in the mixed system = total weight - total solid amount;

[0014] S3. Add the mixed system obtained in S2 to a core mold with dual temperature and pressure control, increase the temperature by 100°C to 300°C, and increase the pressure by 50 MPa to 200 MPa. Simultaneously, inject a small amount of preheated water into the core mold, and maintain the constant temperature and pressure for 12 h to 24 h to obtain a sample after water-rock reaction under compaction.

[0015] S4. Introducing carbon dioxide and hydrogen sulfide gas into the core mold at least three times to obtain a sample after the gas-water-rock reaction under compaction, and collecting and measuring the amount of gas and liquid that did not participate in the reaction;

[0016] S5. Cooling and depressurizing. When the temperature and pressure drop to room temperature and normal pressure, dry the reacted sample and measure the amount of gas and liquid involved in the reaction, i.e., the amount of gas involved in the reaction = the amount of injected gas - the amount of collected gas, and the amount of liquid involved in the reaction = the amount of injected liquid + the residual water content in the mixed system - the amount of collected liquid - the amount of liquid evaporated;

[0017] S6. Collect data on the changes in pressure, temperature and pH value of the core in the core mold over time during the gas-water-rock reaction process, and evaluate whether the pressure, temperature and pH value of the reaction meet the diagenetic environment of the natural dense uranium-bearing sandstone in the study area. If not, adjust the pressure and temperature of step S3, and adjust the liquid injection amount of step S3 and the gas injection amount of S4 according to the calculated influence of the amount of liquid and gas participating in the reaction on the pH value, until the relative error of the pressure, temperature, pH value and measured porosity and permeability of the obtained artificial core and the natural dense uranium-bearing sandstone is within 5%.

[0018] In the above scheme, in step S1, the weight percentages of the raw material components are: quartz sand 60-85%; feldspar 10-25%; clay 2-15%; uranium-containing minerals 0-3% (excluding 0); calcium hydroxide 2-5%; the sum of the weight percentages of the raw materials is 100%; wherein:

[0019] The particle sizes of the quartz sand include 40-60 mesh, 60-80 mesh, 80-100 mesh, 100-150 mesh, 150-200 mesh and above 200 mesh; and the mass ratio of the quartz sand with particle sizes of 40-60 mesh, 60-80 mesh, 80-100 mesh, 100-150 mesh, 150-200 mesh and above 200 mesh is (1.5-2.5): (2.5-5.5): (3.2-5.5): (1.1-3.5): (1.2-1.8): 1;

[0020] The particle sizes of the feldspar include 40-80 mesh, 80-120 mesh, 120-200 mesh and above 200 mesh; and the mass ratio of the feldspar with particle sizes of 40-80 mesh, 80-120 mesh, 120-200 mesh and above 200 mesh is (4.5-8.5): (3.2-6.5): (1.2-3.5): 1;

[0021] The feldspar is potassium feldspar or sodium feldspar, or both;

[0022] The mineral types of the clay include kaolinite, illite, montmorillonite and chlorite, wherein the total weight percentage of kaolinite and illite is not less than 80%, and the total weight percentage of montmorillonite and chlorite is not more than 20%;

[0023] The uranium-containing minerals include pitchblende, uraninite, calcite, titanouraninite and thoronite, wherein the total weight percentage of pitchblende and uraninite is not less than 85%, and the total weight percentage of calcite, titanouraninite and thoronite does not exceed 15%.

[0024] In the above scheme, in step S1, the clay, uranium-containing mineral and calcium hydroxide powder are added to the mixed system of quartz sand and feldspar in 5 to 10 times, and each time is fully stirred for 2 to 5 minutes, and the total stirring time is not less than 30 minutes, so that the clay, uranium-containing mineral and calcium hydroxide powder are evenly attached to the surface of the mixed system of quartz sand and feldspar, and then cooled to room temperature.

[0025] In the above solution, in step S2, the water used to moisten the mixed system is distilled water or groundwater.

[0026] In the above scheme, in step S3, the temperature and pressure increase process is as follows: the initial pressure is 5 MPa, the initial temperature is 20°C~30°C, and the pressure is gradually increased to 50 MPa~200 MPa in steps of 10 MPa. The temperature is increased at a rate of 20°C / hour to 100°C~300°C, ensuring that the pressure and temperature reach the preset values ​​at the same time. During the temperature and pressure increase process, water is injected into the core mold at a rate of 0~10 ml / min, and the temperature and pressure are stabilized within the final pressure and temperature range for 12 h~24 h.

[0027] In the above scheme, the core mold used in step S3 includes a mold barrel, a mold upper cover, a mold lower cover, a loading rod, a liquid injection pipe joint, a gas injection pipe joint, a gas-liquid outflow pipe joint and a heating film; the mold upper cover and the mold lower cover are respectively installed on the upper end and the lower end of the mold barrel in a detachable manner, forming a sample cavity in the middle; the upper end of the loading rod is connected to the universal tensile testing machine, and the lower end of the loading rod passes through the mold upper cover and is slidably sealed with the inner wall of the mold barrel, and the rock sample is axially compacted by the loading rod; the upper end of the loading rod is installed with a liquid injection pipe joint and a gas injection pipe joint. The liquid injection pipe joint and the gas injection pipe joint are connected with the sample cavity through a pipeline passed through the upper cover of the mold, water is injected into the sample cavity through the liquid injection pipe joint, and carbon dioxide and hydrogen sulfide gas are introduced into the sample cavity through the gas pipe joint; a gas-liquid outflow pipe joint is installed on the outside of the lower cover of the mold, and the gas-liquid outflow pipe joint is connected with the sample cavity through a pipeline passed through the lower cover of the mold, and the liquid and gas after the reaction in the sample cavity are discharged through the gas-liquid outflow pipe joint; the heating film is coated on the periphery of the mold cylinder to control the temperature in the sample cavity.

[0028] In the above scheme, step S3 uses a liquid injection system to inject water into the core mold. The liquid injection system includes a first measuring cylinder, a constant speed and constant pressure fluid metering pump, an intermediate pressure vessel and a preheater. The inlet of the constant speed and constant pressure fluid metering pump is connected to the first measuring cylinder, and the outlet is connected to the inlet of the intermediate pressure vessel. The outlet of the intermediate pressure vessel is connected to the preheater, and the outlet of the preheater is connected to the interior of the core mold; the first measuring cylinder is placed on a first electronic balance.

[0029] In the above scheme, in step S4, the initial pressure of the carbon dioxide and hydrogen sulfide gases is 0.1-0.5 MPa, and the pressure is increased to 1 MPa at a rate of 0.2 MPa / h. The reaction is repeated 3-6 times, and the total gas supply time is 12-24 h.

[0030] In the above scheme, step S4 uses a gas injection system to introduce carbon dioxide and hydrogen sulfide gas into the core mold. The gas injection system includes a CO2 gas cylinder, an H2S gas cylinder and a gas flow controller. The CO2 gas cylinder and the H2S gas cylinder are respectively connected to the gas supply main through branch pipelines. The branch pipelines are respectively provided with a pressure regulating valve and a pressure gauge. The gas flow controller is arranged on the gas supply main, and the gas supply main is connected to the interior of the core mold.

[0031] In the above scheme, step S4 uses a gas-liquid collection and metering system to measure the unreacted liquid and gas. The gas-liquid collection and metering system includes a gas-liquid separator, a desiccant, a gas flow meter, a second graduated cylinder and a second electronic balance. The outlet of the core mold is connected to the gas-liquid separator, and the gas outlet of the gas-liquid separator is connected to the desiccant and the gas flow meter in sequence. The liquid outlet of the gas-liquid separator is connected to the second graduated cylinder, and the second graduated cylinder is placed on the second electronic balance.

[0032] In the above scheme, in step S5, the rate of the temperature reduction and pressure reduction process is ensured to be consistent with the rate of the temperature increase and pressure increase process, and the drying time is 10 to 24 hours.

[0033] In the above scheme, in step S6, a data acquisition system is used to collect data on the changes in pressure, temperature and pH value of the core in the core mold over time during the gas-water-rock reaction process. The data acquisition system includes a pressure sensor, a temperature sensor and a pH sensor pre-buried in the inner wall of the core mold, and a computer connected to the signals of each sensor.

[0034] Accordingly, the present invention also provides a device for preparing dense uranium-containing sandstone artificial cores, which is used to implement the above-mentioned preparation method. The device includes a core mold, a liquid injection system, a gas injection system, a gas-liquid collection and metering system, and a data acquisition and control system.

[0035] The core mold comprises a mold barrel, a mold upper cover, a mold lower cover, a loading rod, a liquid injection pipe joint, a gas injection pipe joint, a gas-liquid outflow pipe joint and a heating film; the mold upper cover and the mold lower cover are respectively detachably mounted on the upper and lower ends of the mold barrel, forming a sample cavity in the middle; the upper end of the loading rod is connected to a universal tensile testing machine, and the lower end of the loading rod passes through the mold upper cover and is slidably and sealedly connected to the inner wall of the mold barrel, and the rock sample is axially compacted by the loading rod; the upper end of the loading rod is mounted with a liquid injection pipe joint and a gas injection pipe joint The liquid injection pipe joint and the gas injection pipe joint are connected to the sample cavity through a pipeline passed through the mold upper cover, and water is injected into the sample cavity through the liquid injection pipe joint, and carbon dioxide and hydrogen sulfide gas are introduced into the sample cavity through the gas pipe joint; a gas-liquid outflow pipe joint is installed on the outer side of the mold lower cover, and the gas-liquid outflow pipe joint is connected to the sample cavity through a pipeline passed through the mold lower cover, and the liquid and gas after the reaction in the sample cavity are discharged through the gas-liquid outflow pipe joint; the heating film is coated on the outer periphery of the mold cylinder to control the temperature in the sample cavity;

[0036] The liquid injection system includes a first graduated cylinder, a constant speed and constant pressure fluid metering pump, an intermediate pressure vessel, and a preheater. The inlet of the constant speed and constant pressure fluid metering pump is connected to the first graduated cylinder, and the outlet is connected to the inlet of the intermediate pressure vessel. The outlet of the intermediate pressure vessel is connected to the preheater, and the outlet of the preheater is connected to the liquid injection pipe joint of the core mold.

[0037] The gas injection system includes a CO2 gas cylinder, an H2S gas cylinder and a gas flow controller. The CO2 gas cylinder and the H2S gas cylinder are respectively connected to the gas supply main through branch pipelines. The branch pipelines are respectively provided with a pressure regulating valve and a pressure gauge. The gas flow controller is arranged on the gas supply main, and the gas supply main is connected to the gas injection pipe joint of the core mold;

[0038] The gas-liquid collection and metering system includes a gas-liquid separator, a desiccant, a gas flow meter, a second graduated cylinder, and a second electronic balance. The gas-liquid outflow pipe joint of the core mold is connected to the gas-liquid separator. The gas outlet of the gas-liquid separator is connected to the desiccant and the gas flow meter in sequence. The liquid outlet of the gas-liquid separator is connected to the second graduated cylinder, which is placed on the second electronic balance.

[0039] The data acquisition system includes a pressure sensor, a temperature sensor and a pH sensor pre-buried in the inner wall of the core mold, and a computer connected to the signals of the sensors.

[0040] The beneficial effects produced by the present invention are:

[0041] The method for preparing dense uranium-containing sandstone artificial cores provided by the present invention can realistically simulate the process of hydrothermal fluid injection, as well as sedimentation compaction, cementation, replacement, and dissolution diagenesis during the diagenesis of uranium-containing sandstone; and can regulate the physical properties of the generated artificial cores, including pH value, porosity, and permeability, by feedback-adjusting the temperature, pressure, and gas-liquid injection volume during the preparation process, thereby preparing dense uranium-containing sandstone artificial cores whose pH value, porosity, and permeability all meet the requirements. The cores can be applied to the simulation of fluid flow mechanisms in dense sandstone-type uranium ore reservoirs and the inversion of in-situ leaching mining processes.

[0042] The sample preparation cost of the present invention is low and the production process is simple, and multiple samples can be prepared in a short time for experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 It is a schematic flow chart of the method for preparing a dense uranium-containing sandstone artificial core according to the present invention;

[0045] Figure 2 It is a schematic structural diagram of a device for preparing a dense uranium-containing sandstone artificial core according to the present invention;

[0046] Figure 3 yes Figure 2 A schematic structural diagram of a core mold of the preparation device shown;

[0047] Figure 4 This is a schematic diagram of the appearance of the uranium-containing sandstone artificial core produced in Example 1 of the present invention.

[0048] In the figure: 1. Core mold; 101. Mold cylinder; 102. Mold upper cover; 103. Mold lower cover; 104. Loading rod; 105. Liquid injection pipe joint; 106. Gas injection pipe joint; 107. Gas-liquid outflow pipe joint; 108. Heating film; 109. Upper air permeable plate; 110. Lower air permeable plate; 111. Sealing ring; 112. Guide ring; 113. Rock sample; 114. Temperature controller; 115. Universal tensile testing machine.

[0049] 2. Liquid injection system; 201. First graduated cylinder; 202. First electronic balance; 203. Constant-speed and constant-pressure fluid metering pump; 204. Pressure gauge; 205. Safety valve; 206. Intermediate pressure vessel; 207. Back-pressure valve; 208. Temperature controller; 209. Preheater;

[0050] 3. Gas injection system; 301. CO2 gas cylinder; 302. H2S gas cylinder; 303. Pressure regulating valve; 304. Pressure gauge; 305. Safety valve; 306. Gas flow controller;

[0051] 4. Gas-liquid collection and metering system; 401. Safety valve; 402. Gas-liquid separator; 403. Desiccant; 404. Gas flow meter; 405. Second graduated cylinder; 406. Second electronic balance;

[0052] 5. Data acquisition and control system; 501. Computer. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0054] It should be noted that the illustrations provided in the embodiments of the present invention are only schematic illustrations of the basic concept of the present invention. Therefore, the drawings only show components related to the present invention and are not drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed at will, and the component layout type may also be more complicated.

[0055] In the present invention, it should also be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" and the like are used to indicate positions or locations based on those shown in the accompanying drawings. These terms are intended solely to facilitate the description of the present application and to simplify the description. They are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting the present application. Furthermore, the terms "first" and "second" are used solely for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

[0056] like Figure 1 As shown, the present invention proposes a method for preparing a dense uranium-containing sandstone artificial core, comprising the following steps:

[0057] S1. Mix quartz sand and feldspar of different particle sizes, then add clay, uranium-containing minerals and calcium hydroxide powder and mix thoroughly.

[0058] S2. Spray water on the mixed system obtained in step S1 to moisten it, thereby obtaining a mixed system of water, quartz sand, feldspar, clay, uranium-containing mineral, and calcium hydroxide. After stirring, cool the system to room temperature, and measure the total weight, where the residual water content in the mixed system = the total weight - the total amount of solids (the total amount of mineral components added in step S1).

[0059] S3. Add the mixed system obtained in S2 to a core mold with dual temperature and pressure control, increase the temperature by 100°C to 300°C, and increase the pressure by 50 MPa to 200 MPa. At the same time, inject a small amount of water into the core mold. Maintain the constant temperature and pressure for 12 h to 24 h to obtain a sample after water-rock reaction under compaction.

[0060] In this step, the purpose of increasing temperature and pressure is to simulate the rock diagenesis process. The final temperature and pressure are proportional to the required burial depth of the sample. A certain period of constant temperature and pressure ensures that the diagenetic reaction is fully carried out. The role of the injected water is to simulate the process of hydrothermal fluid injection.

[0061] S4. Inject carbon dioxide and hydrogen sulfide gas into the core mold at least three times in sequence. After the first gas injection is completed, the entire system must be evacuated before the second gas injection to obtain a sample after the gas-water-rock reaction under compaction, and collect and measure the amount of gas and liquid that did not participate in the reaction.

[0062] In this step, the purpose of introducing carbon dioxide gas is to react chemically with calcium hydroxide to form calcium carbonate precipitation, thereby simulating the calcite cementation of uranium-bearing sandstone. The purpose of introducing hydrogen sulfide gas is to react chemically with the minerals in the mixed system to form pyrite precipitation. On the one hand, this simulates the formation of pyrite during the diagenesis of uranium-bearing sandstone, and on the other hand, it promotes the formation of secondary uranium minerals such as hydrous (asphalt) uraninite, calcium uranium mica, and potassium vanadium uraninite at the edge of the pyrite. The above reactions are mainly as follows:

[0063]

[0064] In particular, the introduction of carbon dioxide gas and hydrogen sulfide gas not only causes carbon dioxide to cement into calcium carbonate and hydrogen sulfide to react to form pyrite, but also causes some minerals in the rock sample to undergo replacement and dissolution under high temperature and high pressure, such as the dissolution of carbonates and feldspars, and the interpenetration and replacement of feldspar by carbonates.

[0065] S5. Cool down and reduce the pressure. When the temperature and pressure drop to room temperature and normal pressure, dry the reacted sample for 10 to 24 hours and measure the amount of gas and liquid involved in the reaction, that is, the amount of gas involved in the reaction = the amount of injected gas - the amount of collected gas, and the amount of liquid involved in the reaction = the amount of injected liquid + the residual water content in the mixed system - the amount of collected liquid - the amount of liquid evaporated.

[0066] S6. Collect data on the changes in pressure, temperature and pH value of the core in the core mold over time during the gas-water-rock reaction process, and evaluate whether the pressure, temperature and pH value of the reaction meet the diagenetic environment of the natural dense uranium-bearing sandstone in the study area. If not, adjust the pressure and temperature of steps S3 and S4, and adjust the liquid injection amount of step S3 and the gas-liquid injection amount of step S4 according to the calculated influence of the amount of liquid and gas participating in the reaction on the pH value, until the relative error of the pressure, temperature, pH value and measured porosity and permeability of the obtained artificial core and the natural dense uranium-bearing sandstone is within 5%.

[0067] Further optimization, in step S1, the raw material components are proportioned as much as possible based on the proportion of the main mineral components of natural sandstone-type uranium ore, wherein the weight percentage of each raw material component is: quartz sand 60-85%; feldspar 10-25%; clay 2-15%; uranium-containing minerals 0-3%, excluding 0; calcium hydroxide 2-5%; the sum of the raw material weight percentages is 100%. Among them:

[0068] The particle sizes of quartz sand include 40~60 mesh, 60~80 mesh, 80~100 mesh, 100~150 mesh, 150~200 mesh and above 200 mesh; and the mass ratio of quartz sand with particle sizes of 40~60 mesh, 60~80 mesh, 80~100 mesh, 100~150 mesh, 150~200 mesh and above 200 mesh is (1.5~2.5):(2.5~5.5):(3.2~5.5):(1.1~3.5):(1.2~1.8):1.

[0069] The particle sizes of feldspar include 40~80 mesh, 80~120 mesh, 120~200 mesh and above 200 mesh; and the mass ratio of feldspar with particle sizes of 40~80 mesh, 80~120 mesh, 120~200 mesh and above 200 mesh is (4.5~8.5):(3.2~6.5):(1.2~3.5):1.

[0070] The types of feldspar are potassium feldspar or sodium feldspar, or both.

[0071] The mineral types of clay include kaolinite, illite, montmorillonite and chlorite, among which the total weight percentage of kaolinite and illite is not less than 80%, and the total weight percentage of montmorillonite and chlorite is not more than 20%.

[0072] Uranium-containing minerals include pitchblende, uraninite, uraninite, titanite and uraninite, among which the total weight percentage of pitchblende and uraninite is not less than 85%; the total weight percentage of uraninite, titanite and uraninite does not exceed 15%.

[0073] Further optimization, in step S1, clay, uranium-containing minerals and calcium hydroxide powder are added to the mixed system of quartz sand and feldspar in 5 to 10 times, and each time is fully stirred for 2 min to 5 min, and the total stirring is not less than 30 min, so that the clay, uranium-containing minerals and calcium hydroxide powder are evenly attached to the surface of the mixed system of quartz sand and feldspar, and then cooled to room temperature.

[0074] Further optimization, in step S2, the water used to moisten the mixed system is distilled water or groundwater.

[0075] Further optimization revealed that in step S3, the temperature and pressure increase process is as follows: the initial pressure is 5 MPa, the initial temperature is 20°C–30°C, and the pressure is gradually increased in increments of 10 MPa to 50 MPa–200 MPa. The temperature is increased at a rate of 20°C / hour to 100°C–300°C, ensuring that both pressure and temperature reach the preset values ​​simultaneously. During this temperature and pressure increase process, preheated water is injected into the core mold at a rate of 0–10 ml / min to simulate the effects of hydrothermal fluid injection on the rock. The temperature and pressure are then maintained within the final pressure and temperature range for 12–24 hours to ensure sufficient sample compaction. The entire temperature and pressure increase process is performed in a core mold with dual temperature and pressure control. The water injection rate is controlled between 0 and 10 ml / min to prevent excessively high injection velocity from damaging the rock sample surface and to allow for a prolonged period of low velocity to allow for sufficient reaction between the hydrothermal fluid and the rock sample.

[0076] For further optimization, before starting step S3, it is necessary to perform a degassing experiment on the sample in the core mold and vacuum the entire process using a vacuum pump to ensure that the test data is more realistic.

[0077] Further optimization, the core mold 1 used in step S3 includes a mold barrel 101, a mold upper cover 102, a mold lower cover 103, a loading rod 104, a liquid injection pipe joint 105, a gas injection pipe joint 106, a gas-liquid outflow pipe joint 107 and a heating film 108; the mold upper cover 102 and the mold lower cover 103 are respectively installed on the upper end and the lower end of the mold barrel 101 in a detachable manner, forming a sample cavity in the middle; the upper end of the loading rod 104 is connected to the universal tensile testing machine 115, and the lower end of the loading rod 104 passes through the mold upper cover 102 and is slidably sealed with the inner wall of the mold barrel 101, and the rock sample 113 is axially compacted by the loading rod 104; the upper end of the loading rod 104 is installed with a liquid injection pipe joint. Inlet pipe joint 105 and gas injection pipe joint 106, the liquid injection pipe joint 105 and the gas injection pipe joint 106 are connected to the sample cavity through a pipeline passed through the mold upper cover 102, water is injected into the sample cavity through the liquid injection pipe joint 105, and carbon dioxide and hydrogen sulfide gas are introduced into the sample cavity through the gas pipe joint; a gas-liquid outflow pipe joint 107 is installed on the outside of the mold lower cover 103, the gas-liquid outflow pipe joint 107 is connected to the sample cavity through a pipeline passed through the mold lower cover 103, and the liquid and gas after the reaction in the sample cavity are discharged through the gas-liquid outflow pipe joint 107; a heating film 108 is coated on the outer periphery of the mold cylinder 101, and the temperature in the sample cavity is controlled by a temperature controller 114.

[0078] For further optimization, an upper air permeable plate 109 is mounted on the lower end of the loading rod 104, and a lower air permeable plate 110 is mounted on the upper end of the mold lower cover 103. This prevents mineral particles from clogging the liquid injection pipe joint 105, gas injection pipe joint 106, and gas-liquid outflow pipe joint 107 during compaction. The diameter difference between the upper and lower air permeable plates 109 and 110 and the mold inner diameter is minimized (e.g., <1 mm). The pores on the air permeable plates are evenly distributed and as small as possible (e.g., <0.5 cm) to prevent deformation of the upper and lower bases of the rock sample and loss of the particle skeleton. To prevent deformation of the upper and lower bases of the rock sample and loss of the particle skeleton, filter paper with the same diameter as the upper and lower air permeable plates 110 can be added, or the rock sample can be pre-compacted. The pre-compaction pressure should be as low as possible (e.g., <5 MPa).

[0079] For further optimization, a guide ring 112 is installed on the upper end surface of the mold cover 102, and the loading rod 104 is passed through the guide ring 112; a sealing ring 111 is also provided between the loading rod 104 and the mold cover 102.

[0080] Further optimization is performed, in step S3, a liquid injection system 2 is used to inject water into the core mold 1. The liquid injection system 2 includes a first measuring cylinder 201, a constant speed and constant pressure fluid metering pump 203, an intermediate pressure vessel 206 and a preheater 209. The first measuring cylinder 201 is placed on a first electronic balance 202. The constant speed and constant pressure fluid metering pump 203 is used to adjust the pressure and injection rate of the injected fluid. Its inlet is connected to the first measuring cylinder 201 and its outlet is connected to the inlet of the intermediate pressure vessel 206. The intermediate pressure vessel 206 is used to store the liquid medium injected in the experiment, and its outlet is connected to the preheater 209. The preheater 209 is used to preheat the injected fluid. The preheating temperature is controlled by a temperature controller 208. The outlet of the preheater 209 is connected to the interior of the core mold 1.

[0081] For further optimization, a sealing cover resistant to high temperature and high pressure is provided on the outside of the core mold 1 to ensure that the test data is more authentic.

[0082] Further optimization was performed. In step S4, the initial pressure of carbon dioxide and hydrogen sulfide gas was 0.1-0.5 MPa, and the pressure was increased to 1 MPa at a rate of 0.2 MPa / h. The reaction was repeated 3-6 times, with a total gas supply time of 12-24 h to ensure a more complete reaction between the prepared sample and carbon dioxide and hydrogen sulfide.

[0083] Further optimization, step S4 uses a gas injection system 3 to introduce carbon dioxide and hydrogen sulfide gas into the core mold 1. The gas injection system 3 includes a CO2 gas cylinder 301, an H2S gas cylinder 302 and a gas flow controller 306. The CO2 gas cylinder 301 and the H2S gas cylinder 302 are respectively connected to the gas supply main through branch pipelines. The branch pipelines are respectively provided with a pressure regulating valve 303 and a pressure gauge 304. The gas flow controller 306 is arranged on the gas supply main, and the gas supply main is provided with a safety valve 305. The gas supply main is connected to the inside of the core mold 1.

[0084] Further optimization, step S4 uses a gas-liquid collection and metering system 4 to measure the unreacted liquid and gas. The gas-liquid collection and metering system 4 includes a gas-liquid separator 402, a desiccant 403, a gas flow meter 404, a second measuring cylinder 405 and a second electronic balance 406. The outlet of the core mold 1 is connected to the gas-liquid separator 402 through a safety valve 401. The gas outlet of the gas-liquid separator 402 is connected to the desiccant 403 and the gas flow meter 404 in sequence. The liquid outlet of the gas-liquid separator 402 is connected to the second measuring cylinder 405, and the second measuring cylinder 405 is placed on the second electronic balance 406.

[0085] Further optimization is performed in step S5 to ensure that the rate of the temperature reduction and pressure reduction process is consistent with the rate of the temperature increase and pressure increase process, in order to avoid the rapid drop in temperature and pressure from damaging the sample and to protect the integrity of the sample to the greatest extent.

[0086] Further optimization was performed, and in step S5, the drying time was 10-24 h.

[0087] Further optimizing, in step S6, data acquisition system 5 is used to monitor the time-varying pressure, temperature, and pH value of the core in core mold 1 during the gas-water-rock reaction process. Data acquisition system 5 includes a pressure sensor, a temperature sensor, and a pH sensor disposed on the inner wall of core mold 1, as well as a computer 501 connected to the signals of each sensor. The pressure sensor has a measurement range of 0-200 MPa, the temperature sensor has a measurement range of room temperature to 300°C, and the pH sensor has a measurement range of 0-14.00 pH. This is because the chemical reaction generated during the gas introduction causes the pH of the entire system to change.

[0088] Further optimization is performed in steps S3, S4 and S5. Except for the ports for injecting gas and liquid and collecting unreacted gas and liquid, there is no leakage of gas or liquid during the entire reaction process of the rock sample in the core mold 1, so as to ensure that the test data is more realistic.

[0089] like Figure 2 As shown, the present invention also proposes a device for preparing a dense uranium-containing sandstone artificial core, comprising a core mold 1, a liquid injection system 2, a gas injection system 3, a gas-liquid collection and metering system 4, and a data acquisition and control system. The core mold 1 is used to subject a mixed sandstone powder sample to a high-temperature and high-pressure reaction to obtain a dense uranium-containing sandstone artificial core. The liquid injection system 2 and the gas injection system 3 are respectively used to provide the liquid and gas required for the reaction. The gas-liquid collection and metering system 4 is used to collect and meter the amount of liquid and gas discharged from the core mold 1. The data acquisition and control system is used to collect and monitor temperature, pressure, and pH values ​​during the reaction.

[0090] Core mold 1 Figure 3As shown, it includes a mold cylinder 101, a mold upper cover 102, a mold lower cover 103, a loading rod 104, a liquid injection pipe joint 105, a gas injection pipe joint 106, a gas-liquid outflow pipe joint 107 and a heating film 108; the mold upper cover 102 and the mold lower cover 103 are respectively installed on the upper end and the lower end of the mold cylinder 101 in a detachable manner, forming a sample cavity in the middle; the upper end of the loading rod 104 is connected to the universal tensile testing machine, and the lower end of the loading rod 104 passes through the mold upper cover 102 and is slidably sealed and connected to the inner wall of the mold cylinder 101, and the rock sample is axially compacted by the loading rod 104; the upper end of the loading rod 104 is installed with a liquid injection pipe joint 105 and a gas injection pipe joint 106, and the liquid injection pipe joint 105 and the gas injection pipe joint 106 are installed. The liquid injection pipe joint 106 is connected to the sample cavity through a pipeline passed through the mold upper cover 102, water is injected into the sample cavity through the liquid injection pipe joint 105, and carbon dioxide and hydrogen sulfide gas are introduced into the sample cavity through the gas pipe joint; a gas-liquid outflow pipe joint 107 is installed on the outside of the mold lower cover 103, and the gas-liquid outflow pipe joint 107 is connected to the sample cavity through a pipeline passed through the mold lower cover 103, and the reacted liquid and gas in the sample cavity are discharged through the gas-liquid outflow pipe joint 107; a heating film 108 is coated on the outer periphery of the mold cylinder 101 and is used to control the temperature in the sample cavity. The heating film 108 is connected to the temperature controller 114 signal, and the temperature control range is room temperature to 200°C, the temperature control accuracy is ±0.3°C, and the pressure resistance is better than 100 MPa.

[0091] The liquid injection system 2 includes a first graduated cylinder 201, a constant-speed, constant-pressure fluid metering pump 203, an intermediate pressure vessel 206, and a preheater 209. The inlet of the constant-speed, constant-pressure fluid metering pump 203 is connected to the first graduated cylinder 201, and the outlet is connected to the inlet of the intermediate pressure vessel 206, which stores the injection fluid. The outlet of the intermediate pressure vessel 206 is connected to the preheater 209, which preheats the injection fluid. The outlet of the preheater 209 is connected to the liquid injection pipe joint 105 of the core mold 1. The constant-speed, constant-pressure fluid metering pump 203 has a flow rate range of 0-90 mL / min and a maximum output pressure greater than 100 MPa. A pressure gauge 204 and a safety valve 205 are installed on the pipeline between the constant-speed, constant-pressure fluid metering pump 203 and the intermediate pressure vessel 206; a backpressure valve 207 is installed on the pipeline after the intermediate pressure vessel 206.

[0092] The gas injection system 3 includes a CO2 gas cylinder, an H2S gas cylinder and a gas flow controller 306. The CO2 gas cylinder and the H2S gas cylinder are connected to the gas supply main through branch pipelines respectively. The branch pipelines are respectively provided with a pressure regulating valve 303 and a pressure gauge 304. The gas flow controller 306 is set on the gas supply main, and the gas supply main is connected to the gas injection pipe joint 106 of the core mold 1.

[0093] The gas-liquid collection and metering system 4 includes a gas-liquid separator 402, a desiccant 403, a gas flow meter 404, a second measuring cylinder 405 and a second electronic balance 406. The gas-liquid outflow pipe joint 107 of the core mold 1 is connected to the gas-liquid separator 402, and the gas outlet of the gas-liquid separator 402 is connected to the desiccant 403 and the gas flow meter 404 in sequence. The liquid outlet of the gas-liquid separator 402 is connected to the second measuring cylinder 405, and the second measuring cylinder 405 is placed on the second electronic balance 406.

[0094] The data acquisition system 5 includes a pressure sensor, a temperature sensor and a pH sensor pre-buried in the inner wall of the core mold 1, and a computer connected to the signals of the sensors.

[0095] It should be noted that the preparation equipment of dense uranium-containing sandstone artificial core needs to be resistant to strong acid and strong alkali, and the material in direct contact with the gas can be Hastelloy.

[0096] Example 1:

[0097] A method for preparing a dense uranium-containing sandstone artificial core comprises the following steps:

[0098] S1. Mix quartz sand and feldspar of different particle sizes, then add clay, uranium-containing minerals and calcium hydroxide powder and mix thoroughly.

[0099] Weigh 500 g of quartz sand with the following particle size ratios: 100.05 g (20.01%) of 40-60 mesh, 176.3 g (35.26%) of 60-80 mesh, 87.55 g (17.51%) of 80-100 mesh, 68.05 g (13.61%) of 100-150 mesh, 50.5 g (10.1%) of 150-200 mesh, and 17.55 g (3.51%) of 200 mesh and above;

[0100] Weigh 150g of feldspar, including 100g of potassium feldspar and 50g of sodium feldspar;

[0101] Weigh 20 g of clay, including 10 g of kaolinite, 6 g of illite, and 4 g of montmorillonite;

[0102] Weigh 10 g of uranium-containing minerals from a uranium deposit in the Tuha Basin, Xinjiang.

[0103] Weigh 30 g of calcium hydroxide powder.

[0104] S2. Moisten the mixed system obtained in S1 by spraying a small amount of water 6 times to obtain a mixed system of water, quartz sand, feldspar, clay, uranium-containing minerals and calcium hydroxide. Stir thoroughly for 2 min to 5 min each time, which takes about 30 min in total. After stirring, cool to room temperature and measure the total weight at this time to find that it is 745.12 g. Then, the remaining water content in the mixed system = the total weight 745.12 g - the total solid amount 710 g = 35.12 g.

[0105] S3. Add the mixed system obtained in S2 to the core mold 1 with dual temperature and pressure control, with an initial pressure of 5 MPa and an initial temperature of 22°C. Gradually increase the pressure to 50 MPa in steps of 10 MPa, and increase the temperature at a rate of 20°C / hour to 144°C. At the same time, inject 184.7 g of water into the core mold 1. Maintain the reaction at constant temperature and pressure for 12 hours (no water is injected at this time) to obtain a sample after water-rock reaction under compaction.

[0106] S4. Carbon dioxide and hydrogen sulfide gases are introduced into the core mold 1 sequentially. The initial pressure of the carbon dioxide and hydrogen sulfide gases is 0.1 MPa. The pressure is increased to 1 MPa at a rate of 0.2 MPa / h. Gas supply is continued for 4 hours, and the above reaction process is repeated three times. After the first gas is injected into the core mold 1 (here, carbon dioxide is injected first, followed by hydrogen sulfide), the entire system is evacuated before the second gas is introduced. Finally, the total amount of carbon dioxide injected = 0.0149 kg / h (obtained by the gas flow controller 306) * 4 hours (one gas supply time) * 3 (number of repetitions) = 0.1788 kg, and the total amount of hydrogen sulfide injected = 0.0082 kg / h (obtained by the gas flow controller 306) * 4 hours (one gas supply time) * 3 (number of repetitions) = 0.0984 kg. This yields a sample after the gas-water-rock reaction under compaction. The amount of carbon dioxide that did not participate in the reaction was collected and measured in the gas-liquid collection and metering system 4 = 0.0087 kg / h (obtained by the gas flow meter 404) * 4 h (gas supply time) * 3 (number of repetitions) = 0.1044 kg, the amount of hydrogen sulfide that did not participate in the reaction = 0.0072 kg / h (obtained by the gas flow meter 404) * 4 h (gas supply time) * 3 (number of repetitions) = 0.0864 kg, and the water content was 0.125 kg (obtained by the second electronic balance 406).

[0107] S5. Cool down and reduce the pressure while ensuring that the rate of the cooling and pressure reduction process is consistent with the heating and pressure increase process. When the temperature and pressure drop to room temperature and normal pressure, dry the reacted sample for 10 hours. By collecting water on the outer sealing cover of the core mold 1, the evaporated water content is calculated to be 17.56 g (the total weight of the entire sealing cover before the reaction minus the total weight of the sealing cover after the reaction is the evaporated water content). Finally, the amount of gas and liquid participating in the reaction was measured, that is, the amount of carbon dioxide participating in the reaction = 0.1788kg injected gas amount - 0.1044kg collected gas amount = 0.0744kg, the amount of hydrogen sulfide participating in the reaction = 0.0984kg injected gas amount - 0.0864kg collected gas amount = 0.012kg, the water content participating in the reaction = 184.7g injected liquid amount + 35.12g residual water content in the mixed system - 125.4g collected liquid amount - 12.56g liquid evaporation amount = 81.86g, and the pH value of the rock sample after the reaction was obtained by the pH sensor, which was 6.8, slightly acidic.

[0108] S6. Collect data on the changes in pressure, temperature and pH value of the core in the core mold 1 over time during the gas-water-rock reaction process, and evaluate whether the pressure, temperature and pH value of the reaction meet the natural dense uranium-containing sandstone diagenetic environment in the study area. If not, adjust the pressure and temperature of steps S3 and S4, and adjust the liquid injection amount in step S3 and the gas-liquid injection amount in step S4 based on the calculated influence of the amount of liquid and gas participating in the reaction on the pH value.

[0109] Before successfully obtaining the above-mentioned pressure, temperature and gas-liquid injection volume values ​​that meet the diagenetic environment and physical property parameters of the natural dense uranium-bearing sandstone in the study area (Note: the above descriptions are all data from the fifth test), the process of step S3 and step S4 has been repeated four times; for example, in the second repetition process, the pressure was increased to 50 MPa and the temperature was increased to 156°C, and finally 0.083 kg of carbon dioxide, 0.021 kg of hydrogen sulfide gas and 0.0766 kg of water were reacted to obtain a pH value of 7.6, a porosity of 7.4%, and a density of 2.7 g / cm 3 , permeability 1.7*10 -3 μm 2 The core samples have pH values, porosity and permeability that are neutral to the rock properties of the study area, with porosity of 9%-15% and permeability of 0.2-1.5.*10 -3 μm 2 The situation does not match.

[0110] Based on this, in the subsequent commissioning steps (i.e., the third, fourth, and fifth runs), the main mineral component ratios and the maximum pressure in step S3 were maintained constant. The maximum temperature in step S3 was then gradually decreased by approximately 4°C. The water injection in step S3 was gradually increased by approximately 10g. The carbon dioxide injection in step S4 was gradually increased by 2-6g. The hydrogen sulfide injection was gradually decreased by 2-6g. This was done to control the proportion of minerals (such as calcite) produced by the gas-water-rock reaction. Preliminary findings from these five control cycles indicate that, while maintaining the main mineral component ratios and the maximum control pressure, the porosity of the prepared core can be modestly increased by appropriately lowering the temperature, increasing the injected liquid, and reducing the amount of hydrogen sulfide (to inhibit new mineral formation). However, increasing the injected liquid while increasing the amount of carbon dioxide (to promote new mineral formation) may result in a decrease in the permeability of the rock sample. Therefore, in the artificial rock production process based on the present invention, the physical properties of the generated artificial core can be controlled by the aforementioned pressure, temperature, and gas-liquid injection processes.

[0111] Finally, after five adjustments, the pH value of the reaction formed by 0.0744 kg of carbon dioxide, 0.012 kg of hydrogen sulfide gas and 0.0819 kg of water was 6.8, the porosity was 9%, and the density was 2.5 g / cm 3 , permeability 1.05*10 -3 μm 2 Dense uranium-bearing artificial sandstone core samples, such as Figure 4 As shown. Figure 4 It can be seen that the samples produced by the present invention have complete appearance, uniform mineral distribution, high strength, and can better simulate natural dense uranium-containing artificial samples.

[0112] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, or two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0113] The size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0114] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A method for preparing a dense uranium-containing sandstone artificial core, characterized in that: The following steps are involved: S1. After mixing quartz sand and feldspar of different particle sizes, clay, uranium-containing minerals and calcium hydroxide powder are added and mixed thoroughly; S2. Spray water on the mixed system obtained in S1 to moisten it, to obtain a mixed system of water, quartz sand, feldspar, clay, uranium-containing mineral, and calcium hydroxide. After stirring, cool to room temperature, and measure the total weight. Then, the residual water content in the mixed system = total weight - total solid amount; S3. Add the mixed system obtained in S2 to a core mold with dual temperature and pressure control, increase the temperature by 100°C to 300°C, and increase the pressure by 50 MPa to 200 MPa. Simultaneously, inject a small amount of preheated water into the core mold, and maintain the constant temperature and pressure for 12 h to 24 h to obtain a sample after water-rock reaction under compaction. S4. Introducing carbon dioxide and hydrogen sulfide gas into the core mold at least three times to obtain a sample after the gas-water-rock reaction under compaction, and collecting and measuring the amount of gas and liquid that did not participate in the reaction; S5. Cooling and depressurizing. When the temperature and pressure drop to room temperature and normal pressure, dry the reacted sample and measure the amount of gas and liquid involved in the reaction, i.e., the amount of gas involved in the reaction = the amount of injected gas - the amount of collected gas, and the amount of liquid involved in the reaction = the amount of injected liquid + the residual water content in the mixed system - the amount of collected liquid - the amount of liquid evaporated; S6. Collect data on the changes in pressure, temperature and pH value of the core in the core mold over time during the gas-water-rock reaction process, and evaluate whether the pressure, temperature and pH value of the reaction meet the diagenetic environment of the natural dense uranium-bearing sandstone in the study area. If not, adjust the pressure and temperature of step S3, and adjust the liquid injection amount of step S3 and the gas injection amount of S4 according to the calculated influence of the amount of liquid and gas participating in the reaction on the pH value, until the relative error of the pressure, temperature, pH value and measured porosity and permeability of the obtained artificial core and the natural dense uranium-bearing sandstone is within 5%.

2. The method for preparing a dense uranium-containing sandstone artificial core according to claim 1, characterized in that: In step S1, the weight percentages of the raw material components are: 60-85% of quartz sand; 10-25% of feldspar; 2-15% of clay; 0-3% of uranium-containing minerals, excluding 0; and 2-5% of calcium hydroxide. The total weight percentages of the raw materials are 100%. The particle sizes of the quartz sand include 40 mesh ≤ A < 60 mesh, 60 mesh ≤ B < 80 mesh, 80 mesh ≤ C < 100 mesh, 100 mesh ≤ D < 150 mesh, 150 ≤ E < 200 mesh, and F ≥ 200 mesh; and the mass ratio of A, B, C, D, E, and F is (1.5-2.5): (2.5-5.5): (3.2-5.5): (1.1-3.5): (1.2-1.8): 1; The particle size of the feldspar includes 40 mesh ≤ a < 80 mesh, 80 mesh ≤ b < 120 mesh, 120 mesh ≤ c < 200 mesh and d ≥ 200 mesh; and the mass ratio of a, b, c, d is (4.5-8.5): (3.2-6.5): (1.2-3.5): 1; The feldspar is potassium feldspar or sodium feldspar, or both; The mineral types of the clay include kaolinite, illite, montmorillonite and chlorite, wherein the total weight percentage of kaolinite and illite is not less than 80%, and the total weight percentage of montmorillonite and chlorite is not more than 20%; The uranium-containing minerals include pitchblende, uraninite, calcite, titanouraninite and thoronite, wherein the total weight percentage of pitchblende and uraninite is not less than 85%, and the total weight percentage of calcite, titanouraninite and thoronite does not exceed 15%.

3. The method for preparing a dense uranium-containing sandstone artificial core according to claim 1, characterized in that: In step S1, the clay, uranium-containing mineral and calcium hydroxide powder are added to the mixed system of quartz sand and feldspar in 5 to 10 times, and each time is fully stirred for 2 to 5 minutes, and the total stirring time is not less than 30 minutes, so that the clay, uranium-containing mineral and calcium hydroxide powder are evenly attached to the surface of the mixed system of quartz sand and feldspar, and then cooled to room temperature.

4. The method for preparing a dense uranium-containing sandstone artificial core according to claim 1, characterized in that: In step S3, the temperature and pressure increase process is as follows: the initial pressure is 5 MPa, the initial temperature is 20°C~30°C, and the pressure is gradually increased to 50 MPa~200 MPa in steps of 10 MPa. The temperature is increased at a rate of 20°C / hour to 100°C~300°C, ensuring that the pressure and temperature reach the preset values ​​at the same time. During the temperature and pressure increase process, water is injected into the core mold at a rate of 0~10 ml / min, and the temperature and pressure are stabilized within the final pressure and temperature range for 12 h~24 h.

5. The method for preparing a dense uranium-containing sandstone artificial core according to claim 1, characterized in that: The core mold used in step S3 includes a mold barrel, a mold upper cover, a mold lower cover, a loading rod, a liquid injection pipe joint, a gas injection pipe joint, a gas-liquid outflow pipe joint and a heating film; the mold upper cover and the mold lower cover are respectively installed on the upper end and the lower end of the mold barrel in a detachable manner, forming a sample cavity in the middle; the upper end of the loading rod is connected to the universal tensile testing machine, and the lower end of the loading rod passes through the mold upper cover and is slidably sealed with the inner wall of the mold barrel, and the rock sample is axially compacted by the loading rod; the upper end of the loading rod is installed with a liquid injection pipe joint and a gas injection pipe joint. Pipe joints, the liquid injection pipe joint and the gas injection pipe joint are connected to the sample cavity through a pipe passing through the mold upper cover, water is injected into the sample cavity through the liquid injection pipe joint, and carbon dioxide and hydrogen sulfide gas are introduced into the sample cavity through the gas pipe joint; a gas-liquid outflow pipe joint is installed on the outside of the mold lower cover, the gas-liquid outflow pipe joint is connected to the sample cavity through a pipe passing through the mold lower cover, and the reacted liquid and gas in the sample cavity are discharged through the gas-liquid outflow pipe joint; the heating film is coated on the periphery of the mold cylinder to control the temperature in the sample cavity.

6. The method for preparing a dense uranium-containing sandstone artificial core according to claim 1, characterized in that: In step S3, water is injected into the core mold using a liquid injection system. The liquid injection system includes a first graduated cylinder, a constant speed and constant pressure fluid metering pump, an intermediate pressure vessel, and a preheater. The inlet of the constant speed and constant pressure fluid metering pump is connected to the first graduated cylinder, and the outlet is connected to the inlet of the intermediate pressure vessel. The outlet of the intermediate pressure vessel is connected to the preheater, and the outlet of the preheater is connected to the interior of the core mold. The first graduated cylinder is placed on a first electronic balance.

7. The method for preparing a dense uranium-containing sandstone artificial core according to claim 1, characterized in that: In step S4, the initial pressure of the carbon dioxide and hydrogen sulfide gases is 0.1-0.5 MPa, and the pressure is increased to 1 MPa at a rate of 0.2 MPa / h. The reaction is repeated 3-6 times, and the total gas supply time is 12-24 hours.

8. The method for preparing a dense uranium-containing sandstone artificial core according to claim 1, characterized in that: In step S4, a gas injection system is used to introduce carbon dioxide and hydrogen sulfide gas into the core mold. The gas injection system includes a CO2 gas cylinder, an H2S gas cylinder and a gas flow controller. The CO2 gas cylinder and the H2S gas cylinder are respectively connected to the gas supply main through branch pipelines. The branch pipelines are respectively provided with a pressure regulating valve and a pressure gauge. The gas flow controller is arranged on the gas supply main, and the gas supply main is connected to the interior of the core mold.

9. The method for preparing a dense uranium-containing sandstone artificial core according to claim 1, characterized in that: In step S4, a gas-liquid collection and metering system is used to measure the unreacted liquid and gas. The gas-liquid collection and metering system includes a gas-liquid separator, a desiccant, a gas flow meter, a second graduated cylinder, and a second electronic balance. The outlet of the core mold is connected to the gas-liquid separator, and the gas outlet of the gas-liquid separator is connected to the desiccant and the gas flow meter in sequence. The liquid outlet of the gas-liquid separator is connected to the second graduated cylinder, and the second graduated cylinder is placed on the second electronic balance.

10. The method for preparing a dense uranium-containing sandstone artificial core according to claim 1, characterized in that: In step S5, the rate of the temperature reduction and pressure reduction process is ensured to be consistent with the rate of the temperature increase and pressure increase process, and the drying time is 10 to 24 hours.

11. The method for preparing a dense uranium-containing sandstone artificial core according to claim 1, characterized in that: In step S6, a data acquisition system is used to collect data on the changes in pressure, temperature, and pH value of the core in the core mold over time during the gas-water-rock reaction process. The data acquisition system includes a pressure sensor, a temperature sensor, and a pH sensor pre-buried in the inner wall of the core mold, and a computer connected to the signals of each sensor.

12. A device for preparing dense uranium-containing sandstone artificial core, characterized in that: Used to implement the preparation method according to any one of claims 1 to 11, the preparation device includes a core mold, a liquid injection system, a gas injection system, a gas-liquid collection and metering system, and a data acquisition and control system; The core mold comprises a mold barrel, a mold upper cover, a mold lower cover, a loading rod, a liquid injection pipe joint, a gas injection pipe joint, a gas-liquid outflow pipe joint and a heating film; the mold upper cover and the mold lower cover are respectively detachably mounted on the upper and lower ends of the mold barrel, forming a sample cavity in the middle; the upper end of the loading rod is connected to a universal tensile testing machine, and the lower end of the loading rod passes through the mold upper cover and is slidably and sealedly connected to the inner wall of the mold barrel, and the rock sample is axially compacted by the loading rod; the upper end of the loading rod is mounted with a liquid injection pipe joint and a gas injection pipe joint The liquid injection pipe joint and the gas injection pipe joint are connected to the sample cavity through a pipeline passed through the mold upper cover, and water is injected into the sample cavity through the liquid injection pipe joint, and carbon dioxide and hydrogen sulfide gas are introduced into the sample cavity through the gas pipe joint; a gas-liquid outflow pipe joint is installed on the outer side of the mold lower cover, and the gas-liquid outflow pipe joint is connected to the sample cavity through a pipeline passed through the mold lower cover, and the liquid and gas after the reaction in the sample cavity are discharged through the gas-liquid outflow pipe joint; the heating film is coated on the outer periphery of the mold cylinder to control the temperature in the sample cavity; The liquid injection system includes a first graduated cylinder, a constant speed and constant pressure fluid metering pump, an intermediate pressure vessel, and a preheater. The inlet of the constant speed and constant pressure fluid metering pump is connected to the first graduated cylinder, and the outlet is connected to the inlet of the intermediate pressure vessel. The outlet of the intermediate pressure vessel is connected to the preheater, and the outlet of the preheater is connected to the liquid injection pipe joint of the core mold. The gas injection system includes a CO2 gas cylinder, an H2S gas cylinder and a gas flow controller. The CO2 gas cylinder and the H2S gas cylinder are respectively connected to the gas supply main through branch pipelines. The branch pipelines are respectively provided with a pressure regulating valve and a pressure gauge. The gas flow controller is arranged on the gas supply main, and the gas supply main is connected to the gas injection pipe joint of the core mold; The gas-liquid collection and metering system includes a gas-liquid separator, a desiccant, a gas flow meter, a second graduated cylinder, and a second electronic balance. The gas-liquid outflow pipe joint of the core mold is connected to the gas-liquid separator. The gas outlet of the gas-liquid separator is connected to the desiccant and the gas flow meter in sequence. The liquid outlet of the gas-liquid separator is connected to the second graduated cylinder, which is placed on the second electronic balance. The data acquisition system includes a pressure sensor, a temperature sensor and a pH sensor pre-buried in the inner wall of the core mold, and a computer connected to the signals of the sensors.

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