High-pollution-resistance radioactive isotope tracing microsphere and preparation method thereof

Abstract

The invention discloses a high-pollution-resistance radioactive isotope tracing microsphere and a preparation method thereof. The tracing microsphere is composed of a zeolite / polystyrene composite carrier core, a polyvinyl alcohol curing radioactive source layer, a chitosan hydrophilic pollution-resistance layer and an inorganic-organic composite mineralization shell in sequence. The preparation method comprises the following steps: preparing an iodine-131-containing polyvinyl alcohol aqueous solution and a chitosan acid solution; the preparation method comprises the following steps: mixing zeolite powder and polystyrene powder, and spraying a radioactive polyvinyl alcohol solution in a rolling device to obtain a radioactive isotope-containing microsphere core; spraying a chitosan solution on the surface of the microsphere core by adopting a fluidized coating process, and neutralizing and curing by ammonia water to form a chitosan layer; then the microspheres are placed in a mineralization system containing calcium chloride, sodium carbonate and polyacrylic acid for a reaction, and a calcium-containing inorganic-organic composite mineralization shell layer attached to the outer side is constructed. The adhesion and retention trend of the tracing microsphere in a shaft environment is remarkably reduced, radioactive contamination can be effectively relieved, and the signal-to-noise ratio and profile interpretation precision of tracing logging are improved.

Description

A Highly Anti-fouling Radioactive Isotope Tracing Microsphere and Its Preparation Method Technical Field

[0001] This invention belongs to the technical field of oil and gas field logging and radioactive tracer materials, and relates to the preparation technology of radioactive isotope tracer carrier microparticles for reservoir profile logging. Specifically, it is a highly contamination-resistant radioactive isotope tracer microsphere and its preparation method. By improving the physicochemical properties of the microsphere, it can suppress radioactive contamination caused by crude oil and chemical agents during logging, thereby improving the accuracy of water absorption profile interpretation and logging reliability. Background Technology

[0002] Radioactive tracer technology is widely used in reservoir injection-production profile monitoring, water-absorbing layer identification, and residual oil distribution evaluation. By adding an appropriate amount of radioactive isotope tracer to the injected water or displacement medium and collecting gamma-ray counting curves using downhole logging instruments, the water absorption and fluid migration characteristics of each layer can be quantitatively analyzed. Radioactive isotope tracer microspheres have become an important tracer form in water injection well profile logging due to their advantages such as controllable particle size, good flowability, and clear signal response. Existing radioactive tracer microspheres typically use inorganic porous materials or organic polymer resins as carriers and are loaded with water-soluble radionuclides such as iodine-131. To ensure good suspension and flowability in the wellbore and formation, the microsphere particle size is generally controlled in the range of tens to hundreds of micrometers.

[0003] However, in practical applications, during injection well logging operations, tracer microspheres carrying radionuclides are easily adhered to the crude oil on the surface of downhole tools, especially at structural abrupt changes in downhole tools such as pipe couplings, water distributors, and packers, as well as on the surface of logging instruments. Due to reduced fluid velocity and enhanced turbulence, tracer microspheres are more easily captured and aggregated by the attached oil film, forming localized radioactive anomalies. This radioactive contamination not only generates continuous background signal interference, leading to inaccurate judgment of water absorption layers, but also causes radioactive contamination of downhole tools and logging instruments, increasing the safety risks and equipment maintenance costs of subsequent operations.

[0004] To mitigate the risk of radioactive contamination, existing technologies employ various measures. For example, high-pressure well washing, chemical cleaning, or mechanical scraping are performed before and after tracer injection to remove contaminant layers from the wellbore wall; hydrophilic groups such as surfactants, hydroxyl, or carboxyl groups are introduced onto the surface of tracer microspheres to improve wettability and reduce oil adhesion to the microsphere surface; or a certain number of non-radioactive "cold spheres" are added before formal tracer injection to preferentially occupy easily contaminated areas within the wellbore, thereby reducing the adhesion of radioactive microspheres to some extent. However, these measures still have significant limitations. On the one hand, well washing and mechanical cleaning operations are time-consuming and costly, impacting wellbore integrity and production rhythm, and are difficult to completely remove deep-seated or regenerated oil and polymer deposits; on the other hand, simple surface hydrophilic modification often relies on a single layer of surfactant or the introduction of a small number of hydrophilic functional groups. In complex oil-bearing, polymer-containing, and high-mineralization environments, such single-modification layers are easily sheared off or gradually covered by the oil phase, resulting in limited long-term anti-fouling effects. Furthermore, the "cold ball" placement strategy cannot fundamentally change the surface anti-fouling ability of the tracer microspheres themselves; it only reduces the probability of radioactive contamination by sacrificing part of the carrier, which is still difficult to meet the actual needs of high-precision profile logging and repeated tracing.

[0005] In summary, existing radioisotope tracer microspheres are prone to severe contamination, tracer signal distortion, and high long-term use risks in complex oil-bearing injection and production environments, and these problems have not yet been effectively solved. Therefore, how to develop a radioisotope tracer microsphere preparation technology that still has excellent anti-fouling ability and ensures the stability of radioactive load under conditions such as high oil, high polymer, and high salinity, in order to meet the needs of modern oilfield development for high-precision tracer logging, is an urgent technical problem to be solved in this field. Summary of the Invention

[0006] (I) Purpose of the Invention In view of the above-mentioned defects and deficiencies of the prior art, the present invention aims to provide a highly antifouling radioisotope tracer microsphere and its preparation method. By constructing a multi-layer structure composed of a zeolite / organic resin composite carrier as the core, a chitosan hydrophilic antifouling layer and an inorganic-organic mineralized shell, and combining processes such as spheroidization, fluidized coating and regenerative mineralization treatment, the stable loading and slow release of radioisotopes inside the microspheres can be achieved. At the same time, the surface contamination of the microspheres in oil-containing, polymer-containing and high-mineralization wellbore environments can be significantly reduced, ensuring the signal authenticity and interpretation accuracy of profile tracer logging, and improving the reliability and reusability of injection-production profile monitoring.

[0007] (II) Technical Solution To achieve the purpose of this invention and solve its technical problems, the present invention adopts the following technical solution: The first objective of this invention is to provide a method for preparing highly antifouling radioactive isotope tracer microspheres, used to prepare antifouling radioactive isotope tracer microspheres that have a reduced adhesion and retention tendency in oily and polymer-containing wellbore environments and are suitable for tracer logging, comprising at least the following steps: S100. Preparation of radioactive polyvinyl alcohol solution: Sodium iodide-131 and polyvinyl alcohol are dissolved in deionized water to prepare an aqueous solution of polyvinyl alcohol containing iodide-131 ions; S200. Preparation of chitosan solution: Chitosan is added to an acidic aqueous solution and dissolved under heating and stirring conditions to prepare an acidic aqueous solution of chitosan; S300. Preparation of radioactive isotope-containing microsphere cores: Zeolite powder and polystyrene powder are mixed at a mass ratio of 2:8 to 4:6 and added to a spheroidizing granulation device. During the spheroidizing process, an aqueous solution of polyvinyl alcohol containing iodine-131 is sprayed to form the mixed powder into spheres and load the radioactive isotope into the spherical particles. The resulting spherical particles are then dried and sieved to obtain radioactive isotope-containing microsphere cores with the required particle size; S400. Chitosan coating: The prepared microsphere cores are placed in a fluidized bed coating device, and an acidic aqueous solution of chitosan is sprayed while the particles are in fluidized suspension to form a chitosan coating layer on the surface of the microsphere cores. The mass ratio of particles to chitosan solution is 1:5 to 1:50. After spraying, the resulting coated particles are dried and sieved to obtain chitosan-coated microspheres; S500. Chitosan layer solidification: Chitosan-coated microspheres are immersed in ammonia water to neutralize and solidify the acidic chitosan layer into a stable shell. After cleaning and drying, microspheres with a solidified chitosan layer are obtained. S600. Construction of outer mineralized shell: A first aqueous solution containing calcium chloride and polyacrylic acid and a second aqueous solution containing sodium carbonate are prepared. The second aqueous solution is added to the first aqueous solution to form a mineralization system, and sodium hydroxide is added to adjust the alkalinity of the mineralization system. Then, under stirring conditions, the microspheres obtained in step S500 are added to the mineralization system at a liquid-solid volume ratio of 8:1 to 12:1 to react and form a calcium-containing inorganic-organic composite mineralized shell attached to the outside of the chitosan layer. Finally, after separation, drying and sieving, highly antifouling radioactive isotope tracer microspheres are obtained.

[0008] The second objective of this invention is to provide a highly contamination-resistant radioactive isotope tracer microsphere, which is prepared based on the above-mentioned method for preparing highly contamination-resistant radioactive isotope tracer microspheres of this invention.

[0009] (III) Technical Effects Compared with the prior art, the high-fouling-resistant radioactive isotope tracer microspheres and their preparation method of the present invention have the following beneficial and significant technical effects: (1) The present invention constructs a multi-layer structure of zeolite / polystyrene composite core, polyvinyl alcohol solidified radioactive source, chitosan hydrophilic layer and calcium-containing inorganic-organic composite mineralized shell, so that the radioactive isotope can achieve stable loading and spatial uniform distribution inside the microsphere, significantly reducing the leaching loss of isotopes in injected water and high mineralization environment, while taking into account the γ-ray transmission capability and the mechanical strength of the microsphere, providing a continuous, reliable and high signal-to-noise ratio radioactive tracer signal for oil reservoir water injection profile logging.

[0010] (2) This invention uses the chitosan hydrophilic antifouling layer and the surface mineralization shell to synergistically regulate the surface energy, hydrophilicity and hydrophobicity and electrical characteristics of microspheres. In complex injection water systems containing crude oil, polymers and solid particles, it significantly inhibits the adhesion and coverage of oil and polymers on the surface of microspheres, reduces the retention and accumulation of microspheres in couplings, water distributors and low flow velocity zones of wellbore, thereby effectively reducing the degree of radioactive contamination of wellbore and downhole tools, and improving the authenticity, stability and interlayer identification resolution of profile logging curves.

[0011] (3) The preparation method of the present invention adopts a combination of processes such as spheroidization, fluidized coating and regenerable mineralization pool. The process conditions are mild and do not rely on high temperature and high pressure equipment. The mineralization system can be recycled in multiple batches through testing and replenishment, reducing the consumption of inorganic salts and organic additives and the discharge of waste liquid. At the same time, the formulation of each layer of materials and process parameters have a clear and controllable range, which facilitates large-scale continuous preparation and batch-to-batch performance consistency under industrial conditions, meeting the needs of field promotion and long-term operation in oil fields. Attached Figure Description

[0012] Figure 1 shows a flowchart of the preparation method of the highly antifouling radioisotope tracer microspheres of the present invention; Figure 2 shows a schematic diagram of the structure of the highly antifouling radioisotope tracer microspheres prepared by the present invention. Detailed Implementation

[0013] This invention aims to provide highly contamination-resistant radioactive isotope tracer microspheres and their preparation method. To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be described in more detail below with reference to the accompanying drawings. The described embodiments are some, but not all, embodiments of this invention, and are exemplary and intended to explain the invention, not to limit it. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0014] The materials involved in this invention include, but are not limited to, the materials in the following embodiments, and the preparation methods involved include, but are not limited to, the preparation methods used in the following examples. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those skilled in the art. The reagents or raw materials used in this invention can be obtained through conventional means. Unless otherwise specified, the reagents or raw materials used in this invention are used in accordance with conventional methods in the art or according to the product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein can be applied to the methods of this invention. The preferred embodiments and materials described in this invention are for illustrative purposes only.

[0015] Example 1: Preparation Method of Highly Antifouling Radioactive Isotope Tracing Microspheres As a specific example, the preparation method of highly antifouling radioactive isotope tracer microspheres provided in this embodiment of the invention is used to prepare antifouling radioactive isotope tracer microspheres that have a reduced adhesion and retention tendency in wellbore environments containing oil and polymers and are suitable for radioactive isotope tracer logging. As shown in Figure 1, the preparation method includes at least the following steps: S100. Preparation of radioactive polyvinyl alcohol solution: Sodium iodide-131 and polyvinyl alcohol are dissolved in deionized water to prepare an aqueous solution of polyvinyl alcohol containing iodide-131 ions. The preferred degree of polymerization of polyvinyl alcohol (PVA) is 1700–2400, the preferred degree of hydrolysis is 87–99%, the mass percentage concentration of the PVA aqueous solution is controlled at 3–7%, and the specific activity of sodium iodide-131 is preferably controlled at 10–100 mCi / L. During preparation, PVA is first dissolved in deionized water at 80–95 °C. After complete dissolution, the solution is cooled to room temperature, and then sodium iodide-131 is added and stirred for 30–60 min until homogeneous, ensuring uniform dispersion of the radionuclide in the PVA solution. Furthermore, the mass ratio of sodium iodide-131 to PVA is preferably adjusted to ensure that the radioactivity per unit mass of the dried radioisotope-containing microspheres is within a preset range. This preset range must balance the tracer signal intensity and on-site radiation safety management requirements.

[0016] Preferably, non-radioactive sodium iodide can be further added to the polyvinyl alcohol aqueous solution containing iodine-131 as a carrier iodine source, and the molar ratio of non-radioactive iodide ions to iodine-131 ions can be controlled within the range of 10:1 to 5000:1. This allows the microsphere core formed in subsequent steps to form a solidified phase structure with non-radioactive iodide ions as the carrier and iodine-131 uniformly distributed inside. This reduces the radioactive dose per unit volume of injected liquid while ensuring tracer sensitivity, thereby enhancing the radiation safety and isotope stability during the preparation process and on-site use.

[0017] It should be noted that in step S100, polyvinyl alcohol is used as a radioactive iodine carrier. This is mainly due to the numerous hydroxyl groups on its molecular chain forming multi-point hydrogen bonds and physical entanglements with iodine ions and the zeolite / polystyrene matrix, thus forming a continuous solidified phase after drying, stably anchoring iodine-131 within the microsphere core. In other words, polyvinyl alcohol plays a dual role in this step: firstly, as a hydrophilic polymer binder, it promotes the aggregation of powder particles into spheres through liquid bridging forces during the subsequent spheroidization process; secondly, the hydroxyl groups on its molecular chain can form hydrogen bonds with iodine ions, enhancing the dispersion uniformity and solidification stability of iodine-131 within the microsphere core. In this step, by first completely dissolving polyvinyl alcohol at a higher temperature and then adding a radioactive iodine source at room temperature, it is beneficial to avoid the decomposition or activity loss of iodine-131 under high temperature conditions. At the same time, it ensures that polyvinyl alcohol fully swells to form a homogeneous colloidal solution, providing a stable dispersion medium environment for iodine-131. Meanwhile, the use of non-radioactive sodium iodide to form a continuous iodine salt solidified phase allows iodine-131 to be macroscopically diluted and distributed in the carrier iodine matrix. This ensures good spatial uniformity during subsequent spheroidization, drying, and water dilution processes, thus balancing tracer sensitivity and radiation safety.

[0018] S200. Chitosan Solution Preparation: Chitosan is added to an acidic aqueous solution and dissolved under heating and stirring conditions to prepare an acidic chitosan aqueous solution. The acidic aqueous solution is preferably an acetic acid aqueous solution, with a mass percentage concentration preferably controlled at 1-3%. The mass percentage concentration of chitosan in the acidic chitosan aqueous solution is preferably set to 0.5-1.5%, and the degree of deacetylation of chitosan is preferably set to 75-95%. The solution is stirred at 50-70 °C for 1-3 hours until the chitosan is completely dissolved, then cooled to room temperature for later use. During the heating and stirring process, the chitosan solution needs to be vacuum degassed to eliminate microbubbles inside the solution, ensuring the density and uniformity of the subsequent coating layer and preventing coating defects caused by bubble rupture.

[0019] It should be noted that acetic acid is used to prepare the acidic aqueous solution of chitosan in step S200. This is because, on the one hand, acetic acid's reversible protonation effect on the amino groups of chitosan promotes the full expansion of chitosan segments and the formation of a stable solution; on the other hand, the acetic acid residue is low and its volatility is moderate, allowing for efficient removal during subsequent neutralization and drying processes, reducing interference with the mineralization reaction. Vacuum degassing not only eliminates pinholes and voids in the coating layer caused by air bubbles in the solution, but also improves the continuity of droplet film formation and the density of the shell layer during fluidized bed spraying, providing a foundation for achieving uniform coating and subsequent gel curing.

[0020] S300. Preparation of radioactive isotope-containing microsphere cores: Zeolite powder and polystyrene powder are mixed at a mass ratio of 2:8 to 4:6 and then added to a spheroidizing granulation device. During the spheroidizing process, an aqueous solution of polyvinyl alcohol containing iodine-131 is sprayed to form the mixed powder into spheres and load the radioactive isotope into the spherical particles. Subsequently, the obtained spherical particles are dried and sieved to obtain radioactive isotope-containing microsphere cores with the required particle size.

[0021] In this embodiment of the invention, the zeolite powder is a crystalline aluminosilicate material with an ion-exchangeable pore structure (preferably, the selected zeolite type has a pore structure capable of forming physical adsorption and / or ion exchange binding with iodine-131, thereby providing additional inorganic support sites outside the polystyrene matrix), and its mesh size is controlled between 200 and 400 mesh; the polystyrene powder is a thermoplastic resin powder used as the organic framework for forming microsphere cores during the spheroidization process, and its mesh size is controlled between 80 and 150 mesh; the mass ratio of zeolite powder to polystyrene powder is controlled between 2:8 and 4:6 to ensure that the subsequently formed microsphere cores have both sufficient mechanical strength and a suitable pore structure, providing an inorganic-organic composite loading environment for iodine-131, thereby improving the stability and anti-loss ability of radioactive isotopes during wellbore injection and formation seepage; the amount of polyvinyl alcohol aqueous solution containing iodine-131 added is 0.8 to 1.3 times the total mass of the mixed powder, and the rotation speed of the spheroidizing granulation device is controlled between 15 and 30 rpm, and the spheroidization time is controlled between 20 and 60 minutes. The blowing rate is controlled at 5-15 ml / min, and the spraying rate of polyvinyl alcohol aqueous solution containing iodine-131 during the spheroidization process is controlled to keep the mixed powder in a wet but non-sticky state so as to induce the powder to self-assemble into spheres by utilizing the synergistic effect of liquid bridge force and centrifugal force. The drying process adopts a step-by-step heating method, first drying at a low temperature of 45-55 ℃ for 2-4 hours, and then heating to a medium temperature of 70-90 ℃ for 100-150 min to avoid microsphere cracking caused by rapid evaporation of moisture. Finally, the microspheres with radioactive isotope cores with a particle size of 10-2000 μm are obtained by sieving, ensuring that the microsphere cores have a uniform spherical morphology and a suitable particle size distribution.

[0022] As a preferred example, the zeolite powder used is modified hydrophobic zeolite powder. The modification treatment includes: immersing the zeolite powder in a silane coupling agent solution, wherein the silane coupling agent is selected from at least one of methyltrimethoxysilane and dimethyldimethoxysilane, the mass percentage concentration of the silane coupling agent solution is 2-5%, the immersion time is 4-8 hours, and then drying and curing at 100-120 °C for 2-4 hours. After modification treatment, hydrophobic zeolite powder is obtained, and a hydrophobic siloxane layer is formed on its surface, which makes the microsphere core more hydrophobic and oil-repellent, significantly reducing the tendency of microspheres to adhere to oil in oily well environments and improving the anti-fouling ability of tracer microspheres.

[0023] It should be noted that step S300, through the composite design of zeolite powder and polystyrene powder, enables the microsphere core to function as both an inorganic porous support phase and an organic supporting framework: zeolite, as a porous inorganic material, uses its pore structure to physically adsorb and fix iodine-131 ions through ion exchange, forming inorganic support sites; polystyrene, as a thermoplastic resin, undergoes plastic deformation under mechanical and liquid bridging forces during the spheroidization process, encapsulating the zeolite particles and forming a dense organic matrix framework. The design principle of the stepwise heating and drying strategy is: in the low-temperature stage, surface moisture is slowly removed to avoid microsphere cracking caused by internal stress from rapid moisture evaporation; in the medium-temperature stage, polyvinyl alcohol film formation and curing are promoted, enhancing the mechanical strength and structural stability of the microsphere core. During the spheroidizing process, by controlling the powder particle size, spheroidizing speed, air volume, and stepwise heating and drying curve, the powder particles can gradually grow and tend to become spherical under the coupled effect of liquid bridging force, centrifugal force, and thermal shrinkage. Stepwise heating and drying reduces the internal stress gradient by slowly releasing moisture, avoids the generation of radial cracks, and ensures the integrity and stability of the core layer structure, providing a foundation for the stable construction of multi-layer shell structures.

[0024] S400. Chitosan coating: The prepared microsphere cores are placed in a fluidized coating device, and an acidic aqueous solution of chitosan is sprayed on the microsphere cores in a fluidized suspension state to form a chitosan coating layer on the surface of the microsphere cores. The mass ratio of particles to chitosan solution is 1:5 to 1:50. After the spraying is completed, the coated particles are dried and sieved to obtain chitosan-coated microspheres. Preferably, the fluidized bed coating device adopts a bottom-up air supply structure. The airflow velocity is adjusted to a range that ensures the microsphere core particles form a uniform fluidized suspension state while avoiding collision and breakage. The airflow rate is adjusted so that the height of the fluidized bed is 1 / 2 to 2 / 3 of the total height of the drying chamber. Acidic chitosan aqueous solution is atomized into the fluidized bed through top or bottom spray guns. The atomization pressure is set to 0.15-0.25 MPa, and the spray droplet size is controlled between 20 and 150 μm. The spraying rate is adjusted to match the fluidization state and ensure uniform deposition of chitosan on the surface of the microsphere cores. The spraying process is intermittent, stopping spraying after every 5-10 minutes and continuing fluidized drying for 2-5 minutes, repeating this cycle until the preset coating thickness is achieved. During the coating process, the inlet air temperature is controlled at 80-100 ℃, and the material temperature is maintained at 70-90 ℃. At ℃, the moisture in chitosan gradually evaporates and eventually forms chitosan-coated microspheres with a continuous, flat surface that do not agglomerate.

[0025] It should be noted that the fluidized bed coating method using bottom-up air supply in this step allows the microsphere cores to continuously tumble and disperse in three-dimensional space, avoiding bridging, adhesion, and localized accumulation problems that are prone to occur in traditional roller coating or dip coating processes. The fluidized bed intermittent spraying process enables a cyclic deposition pattern of spraying-drying-re-spraying on the particle surface, avoiding agglomeration caused by excessive wetting in a single step. By precisely controlling the droplet size, spraying rate, and bed temperature, chitosan is deposited layer by layer on the microsphere surface and rapidly dehydrated and fixed, forming an organic layer with controllable thickness and a smooth surface. This chitosan layer serves both as the bottom layer for subsequent mineralization interfacial reactions, providing coordination sites such as amino and hydroxyl groups, and as a flexible buffer layer, dispersing stress when the outer shell is not under stress, preventing the overall shell from becoming brittle.

[0026] S500. Chitosan layer curing: Chitosan-coated microspheres are immersed in ammonia water to neutralize and solidify the acidic chitosan layer into a stable shell. After cleaning and drying, microspheres with a cured chitosan layer are obtained. Preferably, the ammonia solution has a mass percentage concentration of 0.5-2%. Chitosan-coated microspheres are soaked in ammonia solution for 5-15 minutes at a temperature of 20-30°C, using intermittent oscillation at a frequency of 80-120 times / minute. This ensures the ammonia solution fully penetrates the acidic chitosan layer, neutralizing it and causing cross-linking and solidification to form a chitosan gel framework layer. The mechanism of this solidification reaction utilizes the alkaline environment of ammonia solution to eliminate the positive charge of amino groups on the chitosan molecular chains through deprotonation, disrupting its solubility equilibrium under acidic conditions. This causes a conformational change in the chitosan molecular chains, leading to precipitation from the solution and a sol-gel phase transition. This transforms the water-soluble chitosan acetate layer into a water-insoluble and dense chitosan gel framework layer. The microspheres are then washed with deionized water until the solution pH is close to neutral to remove residual free ammonia and soluble salts, and dried at 70-90°C for 80-150 minutes. min ensures that the resulting cured chitosan layer has high mechanical strength and swelling resistance under high shear flow field and high mineralization environment of injected water.

[0027] It should be noted that the neutralization of the acidic chitosan salt layer using low-concentration ammonia in this step is essentially a phase transition from a soluble polyelectrolyte to an insoluble neutral polysaccharide network. After deprotonation, the electrostatic repulsion between chitosan molecules is significantly weakened, and hydrogen bonding and hydrophobic interactions become dominant, causing the chain segments to re-entangle and construct a three-dimensional gel framework. By controlling the ammonia concentration, soaking time, and temperature, the density and pore structure of the gel network can be adjusted, thereby affecting the mechanical strength and water stability of the shell. Moderate oscillation promotes uniform ammonia penetration, avoiding the uneven phenomenon of the outer layer solidifying while the inner layer remains swollen, thus ensuring the uniformity of the overall stress and chemical reaction of the shell during mineralization.

[0028] S600. Construction of the outer mineralized shell: Prepare a first aqueous solution containing calcium chloride and polyacrylic acid and a second aqueous solution containing sodium carbonate. Add the second aqueous solution to the first aqueous solution to form a mineralization system, and add sodium hydroxide to adjust the alkalinity of the mineralization system. Then, under stirring conditions, add the microspheres obtained in step S500 to the mineralization system at a liquid-solid volume ratio of 8:1 to 12:1 to react and form a calcium-containing inorganic-organic composite mineralized shell attached to the outside of the chitosan layer. Finally, after separation, drying and sieving, highly antifouling radioisotope tracer microspheres are obtained.

[0029] In this embodiment of the invention, the preferred mass percentage concentration of calcium chloride in the first aqueous solution is 0.08-0.20%, and the preferred mass percentage concentration of polyacrylic acid is 0.003-0.010%. The concentration and mass ratio of calcium chloride to polyacrylic acid are controlled within a range that allows for the formation of a stable calcium-containing organic complex and facilitates subsequent calcium carbonate deposition. The preferred mass percentage concentration of sodium carbonate in the second aqueous solution is 0.08-0.20%. After mixing the first and second aqueous solutions, sodium hydroxide (preferably 0.003-0.008% by mass) is added to adjust the alkalinity of the system and the pH value is adjusted to 8.0-12.0. Then, the microspheres obtained in step S500 are added to the mineralization system at a liquid-to-solid volume ratio of 8:1 to 12:1, and the mixture is heated for 20-40 minutes. Stirring at ℃ for 6-24 hours to maintain the mineralization reaction allows an inorganic-organic composite mineralized shell composed of calcium carbonate and calcium-polyacrylic acid composite structure to be generated in situ on the surface of the chitosan layer. After the mineralization reaction is completed, residual soluble inorganic salts and free polyacrylic acid are removed by solid-liquid separation, washing and drying, and finally highly resistant radioactive isotope tracer microspheres are obtained by sieving.

[0030] Preferably, in step S600, 0.002-0.008% polyacrylic acid is added to the mineralization system as an aggregation state regulator. The addition of polyacrylic acid can work synergistically with the chitosan layer to obtain amorphous calcium carbonate. Polyacrylic acid and amorphous calcium carbonate construct micro-nano-scale roughness on the surface of microspheres. Combined with the hydrophilicity of polyacrylic acid, they synergistically achieve superhydrophilic surface properties with a contact angle of less than 5°, so that the microspheres form a stable hydration layer in the aqueous phase, effectively blocking the approach and adhesion of oil phase substances and greatly improving the anti-oil stain performance.

[0031] Preferably, after the mineralization reaction is completed to form a calcium-containing inorganic-organic composite mineralized shell, the surface is further modified by hydrophilic modification: the mineralized microspheres are immersed in an aqueous solution containing a zwitterionic surfactant, wherein the zwitterionic surfactant is selected from at least one of dodecyl dimethyl betaine and tetradecyl dimethylamine oxide, and its mass percentage concentration is controlled at 0.05-0.2%, the immersion temperature is 30-40 ℃, the immersion time is 20-40 min, and the immersion process is ultrasonically assisted, with the ultrasonic power controlled at 100-200 W and the ultrasonic time being 10-20 minutes. By utilizing the calcium ion sites or residual active groups on the surface of the mineralized shell, amphoteric surfactant molecules are formed on the surface of the mineralized shell through electrostatic adsorption or surface grafting polymerization, constructing a nano-thick, strongly hydrated layer on the outermost layer of the microspheres. This further enhances the hydrophilicity and anti-oil properties of the microsphere surface. At the same time, ultrasonic treatment promotes the uniform dispersion of surfactants and their penetration into the surface pores, ensuring the durability and stability of the modification effect. This allows the microspheres to maintain excellent anti-fouling performance in wellbore environments such as polymer flooding.

[0032] Preferably, in step S600, after the mineralization reaction is completed, the mineralization system is filtered and separated and the mother liquor is recovered. By detecting the concentration of calcium ions and carbonate ions in the mother liquor and supplementing with calcium chloride, sodium carbonate and sodium hydroxide solutions of corresponding mass fractions, the ionic strength and pH of the mineralization system are kept within a preset range. This allows the same mineralization pool to be continuously used for the construction of multiple batches of outer mineralization shells, ensuring batch-to-batch consistency in the thickness and surface properties of the outer mineralization shell of the highly fouling-resistant radioisotope tracer microspheres obtained from different batches.

[0033] Preferably, by comprehensively controlling the solid addition amount, curing time, and drying conditions of the radioactive isotope-containing microsphere core, chitosan coating layer, and outer mineralized shell in steps S300-S600, the finally obtained highly antifouling radioactive isotope tracer microspheres have a multi-layered concentric shell structure in the radial direction, consisting of a zeolite / polystyrene composite core, a polyvinyl alcohol / iodine-131 layer, a cured chitosan layer, and a calcium-containing inorganic-organic composite mineralized shell layer, from the inside out. The core and polyvinyl alcohol / iodine-131 layer account for 60-85% of the total mass of the microspheres, the chitosan layer accounts for 5-20% of the total mass of the microspheres, and the outer mineralized shell accounts for 5-20% of the total mass of the microspheres, forming a multi-layered synergistic antifouling and stable load structure.

[0034] Preferably, in steps S400 and S600, by adjusting the solid content of the chitosan solution, the spraying rate, the mineralization reaction time, and the molar ratio of calcium source to carbonate in the mineralization system, the apparent static contact angle of the finally obtained high-fouling-resistant radioisotope tracer microspheres in simulated oil-contaminated and polymer-contaminated injected water is not greater than 60°, and after repeated cycles of contact with oil-contaminated solution under preset stirring and shearing conditions, the increase in the amount of oil adhering to the surface of the microspheres relative to the initial mass of the microspheres does not exceed 5%, thereby achieving quantitative control of the antifouling performance of the microsphere surface.

[0035] Preferably, by comprehensively adjusting the mass ratio of zeolite to polystyrene, the spheroidizing and drying conditions, and the deposition amount of each shell material in steps S300-S600, the median particle size of the finally obtained high-fouling-resistant radioisotope tracer microspheres is controlled within 50-2000 μm, the ratio of D10 to D90 of the particle size distribution is not greater than 3.0, and the true density of the microspheres is controlled within 0.9-1.2 g / cm³. 3 This allows the microspheres to settle at a rate that matches the injection water flow rate, enabling them to enter the target absorbent layer with the fluid while minimizing their tendency to remain in low-velocity areas of the wellbore for extended periods.

[0036] Preferably, by comprehensively adjusting the ammonia concentration, chitosan solid content, mineralization reaction pH, and mineralization time in steps S500 and S600, the crosslinking density of the solidified chitosan layer is matched with the density of the outer inorganic-organic composite mineralized shell. This ensures that the resulting highly antifouling radioisotope tracer microspheres do not experience significant cracking, peeling, or swelling instability in a high-temperature, high-mineralization water environment with a temperature range of 80-120 °C and a mineralization degree of 50-200 g / L. This guarantees the synergistic maintenance of its antifouling performance and radioactive load stability during long-term tracing under complex reservoir conditions.

[0037] It should be noted that the formation of the outer mineralized shell in step S600 is based on an in-situ mineralization deposition mechanism: the amino and hydroxyl groups on the surface of the chitosan layer provide heterogeneous nucleation sites for calcium carbonate crystal nuclei, Ca... 2+ First, it undergoes a complexation reaction with the carboxyl groups of polyacrylic acid to form a calcium-polyacrylic acid complex, followed by CO3... 2- The addition of [a specific ingredient] triggers the aggregation and precipitation of calcium carbonate. Polyacrylic acid molecules, acting as growth regulators in the aggregated state, embed themselves in the interstices of calcium carbonate particles, forming a composite mineralized shell interwoven with inorganic particles and organic segments. Controlling the pH of the mineralization reaction within the alkaline range promotes the supersaturated precipitation of calcium carbonate while maintaining the structural stability of the chitosan gel layer. The construction of the mineralized shell endows the microsphere surface with high hydrophilicity and oil resistance, while simultaneously enhancing the overall mechanical strength of the structure.

[0038] The highly contamination-resistant radioisotope tracer microspheres finally prepared by this invention have the structure shown in Figure 2. The microspheres exhibit a typical multi-layered concentric spherical shell composite structure, which, from the inside out, includes a microsphere core layer 10, a solidified chitosan layer 20, and a calcium-containing inorganic-organic composite mineralized shell layer 30. Figure 10 shows the core of a radioactive isotope-containing microsphere, composed of hydrophobically modified zeolite powder and polystyrene powder, coated with a polyvinyl alcohol / iodine-131 complex layer. This core structure achieves efficient immobilization and long-term stable retention of radioactive nuclides through the ion exchange adsorption capacity of zeolite, the complexation and fixation effect of polyvinyl alcohol, and the hydrolysis resistance provided by hydrophobic modification. Figure 20 shows a chitosan-cured coating layer, which forms a dense protective film through cross-linking and curing in an ammonia atmosphere, serving the dual purpose of sealing and immobilizing radioactive nuclides and enhancing mechanical strength. Figure 30 shows an amorphous calcium carbonate / polyacrylic acid composite mineralized shell modified with a zwitterionic surfactant. This layer has a multi-layered hierarchical structure and a superhydrophilic surface, effectively preventing oil contamination adhesion and maintaining the high hydrophilicity of the microsphere surface. The multi-layered composite structure design of this invention enables the microspheres to possess excellent anti-fouling performance, radioactive nuclide immobilization stability, and wellbore migration performance in complex oil reservoir environments.

[0039] Example 2:

[0040] Example 2 uses the same preparation method as Example 1, with the following specific parameters: S100. Polyvinyl alcohol degree of polymerization is 1700, degree of alcoholysis is 87%, polyvinyl alcohol aqueous solution mass percentage concentration is 3%, sodium iodide specific activity is 10 mCi / L, and the molar ratio of non-radioactive iodide ions to iodide-131 ions is 10:1; S200. Acetic acid aqueous solution mass percentage concentration is 1%, chitosan mass percentage concentration is 0.5%, chitosan deacetylation degree is 75%, heating temperature is 50℃, stirring time is 1 hour; S300. Zeolite powder to polystyrene powder mass ratio is 2:8, zeolite powder mesh size is 200 mesh, polystyrene powder mesh size is 80 mesh, the amount of polyvinyl alcohol aqueous solution containing iodide-131 added is 0.8 times the total mass of the mixed powder, spheroidizing speed is 15 rpm, spheroidizing time is 20 min, air volume is 5 ml / min, low temperature drying temperature is 45℃ and time is 2 hours, medium temperature drying temperature is 70℃ and time is 100 minutes. The process involved sieving to obtain microspheres with a particle size of 200 μm; hydrophobic modification of zeolite powder was performed, with methyltrimethoxysilane as the silane coupling agent at a mass percentage concentration of 2%, soaking time of 4 hours, and drying temperature of 100℃ for 2 hours; S400: the mass ratio of particles to chitosan solution was 1:5, the airflow was adjusted to ensure the mainstream layer height of the particles accounted for 1 / 2 of the total height of the drying chamber, the atomization pressure was 0.25 MPa, the droplet size was 20 μm, the intermittent spraying cycle was 5 minutes of spraying followed by 5 minutes of rest, the airflow temperature was 80℃, and the material temperature was 65℃; S500: the ammonia water mass percentage concentration was 0.5%, the soaking time was 5 minutes, the soaking temperature was 20℃, the oscillation frequency was 80 times / minute, and the drying temperature was 70℃ for 80 minutes; S600. The first aqueous solution contained 0.08% calcium chloride and 0.003% polyacrylic acid. The second aqueous solution contained 0.08% sodium carbonate and 0.003% sodium hydroxide. The system pH was 8.0, the liquid-to-solid volume ratio was 8:1, the reaction temperature was 20℃, and the stirring time was 6 hours. The polyacrylic acid concentration was 0.002%. The amphoteric surfactant was dodecyl dimethyl betaine with a mass percentage of 0.05%. The soaking temperature was 30℃ for 20 minutes, and the ultrasonic power was 100 W for 10 minutes.

[0041] The final high-contamination-resistant radioisotope tracer microspheres consisted of a core and polyvinyl alcohol / iodine-131 layer accounting for 85% of the total mass, a chitosan layer accounting for 5%, and an outer mineralized shell accounting for 10%. The median particle size was 200 μm, the particle size distribution D10 / D90 was 2.8, and the true density was 0.97 g / cm³. 3 .

[0042] Example 3:

[0043] Example 3 uses the same preparation method as Example 1, with the following specific parameters: S100. Polyvinyl alcohol degree of polymerization is 2050, degree of alcoholysis is 93%, polyvinyl alcohol aqueous solution mass percentage concentration is 5%, sodium iodide specific activity is 55 mCi / L, and the molar ratio of non-radioactive iodide ions to iodide-131 ions is 255:1; S200. Acetic acid aqueous solution mass percentage concentration is 2%, chitosan mass percentage concentration is 1.0%, chitosan deacetylation degree is 85%, heating temperature is 60℃, and stirring time is 2 hours; S300. Zeolite powder to polystyrene powder mass ratio is 3:7, zeolite powder mesh size is 300 mesh, polystyrene powder mesh size is 115 mesh, the amount of polyvinyl alcohol aqueous solution containing iodide-131 added is 1.05 times the total mass of the mixed powders, spheroidizing speed is 22 rpm, spheroidizing time is 40 min, and air volume is 10. The drying process involved several steps: a 100 ml / min drying rate, a low-temperature drying temperature of 50℃ for 3 hours, a medium-temperature drying temperature of 80℃ for 125 min, and sieving to obtain microspheres with a particle size of 350 μm. Zeolite powder underwent hydrophobic modification treatment. The silane coupling agent was a mixture of methyltrimethoxysilane and dimethyldimethoxysilane (mass ratio 1:1) with a mass percentage concentration of 3.5%. The soaking time was 6 hours, and the drying temperature was 110℃ for 3 hours. For S400, the mass ratio of granules to chitosan solution was 1:27. The airflow was adjusted so that the mainstream layer height occupied 7 / 12 of the total height of the drying chamber. The atomization pressure was 0.20 MPa, the droplet size was 85 μm, and the intermittent spraying cycle was 7 minutes of spraying followed by a 3-minute stop. The airflow temperature was 89℃, and the material temperature was 75℃. For S500, the ammonia concentration was 1.25%. The soaking time was 10 minutes, the soaking temperature was 25℃, the oscillation frequency was 100 times / min, and the drying temperature was 80℃ for 115 minutes. min; S600. The first aqueous solution contains 0.14% calcium chloride and 0.0065% polyacrylic acid. The second aqueous solution contains 0.14% sodium carbonate and 0.0055% sodium hydroxide. The system pH is 10.0, the liquid-to-solid volume ratio is 10:1, the reaction temperature is 30℃, and the stirring time is 15 hours. The polyacrylic acid concentration is 0.005%. The amphoteric surfactant is a mixture of dodecyl dimethyl betaine and tetradecyl dimethylamine oxide (mass ratio 1:1) with a mass percentage concentration of 0.125%. The soaking temperature is 35℃ and the time is 30 min. The ultrasonic power is 150 W and the time is 15 min.

[0044] The final high-contamination-resistant radioisotope tracer microspheres consisted of a core and polyvinyl alcohol / iodine-131 layer accounting for 72% of the total mass, a chitosan layer accounting for 13%, and an outer mineralized shell accounting for 15%. The median particle size was 400 μm, the particle size distribution (D10 / D90) was 2.4, and the bulk density was 1.05 g / cm³. 3 .

[0045] Example 4:

[0046] Example 4 uses the same preparation method as Example 1, with the following specific parameters: S100. Polyvinyl alcohol degree of polymerization is 2400, degree of alcoholysis is 99%, polyvinyl alcohol aqueous solution mass percentage concentration is 7%, sodium iodide specific activity is 100 mCi / L, and the molar ratio of non-radioactive iodide ions to iodide-131 ions is 5000:1; S200. Acetic acid aqueous solution mass percentage concentration is 3%, chitosan mass percentage concentration is 1.5%, chitosan deacetylation degree is 95%, heating temperature is 70℃, and stirring time is 3 hours; S300. Zeolite powder to polystyrene powder mass ratio is 4:6, zeolite powder mesh size is 400 mesh, polystyrene powder mesh size is 150 mesh, the amount of polyvinyl alcohol aqueous solution containing iodide-131 added is 1.3 times the total mass of the mixed powders, spheroidizing speed is 30 rpm, spheroidizing time is 60 min, and air volume is 15. The drying process involved several steps: a 500 μm microsphere core was obtained by sieving at a low temperature of 55℃ for 4 hours and a medium temperature of 90℃ for 150 min; zeolite powder underwent hydrophobic modification treatment; dimethyldimethoxysilane was used as the silane coupling agent at a mass percentage concentration of 5%; soaking time was 8 hours; and drying temperature was 120℃ for 4 hours. For S400, the mass ratio of particles to chitosan solution was 1:50; the airflow was adjusted to ensure the mainstream layer height occupied 2 / 3 of the total height of the drying chamber; the atomization pressure was 0.15 MPa; the droplet size was 150 μm; the intermittent spraying cycle was 10 min spraying followed by a 2 min stop; the airflow temperature was 100℃; and the material temperature was 85℃. For S500, the ammonia concentration was 2%; soaking time was 15 min; soaking temperature was 30℃; the oscillation frequency was 120 times / min; and drying temperature was 90℃ for 150 min. For S600... The first aqueous solution contained 0.20% calcium chloride and 0.010% polyacrylic acid. The second aqueous solution contained 0.20% sodium carbonate and 0.008% sodium hydroxide. The system pH was 12.0, the liquid-to-solid volume ratio was 12:1, the reaction temperature was 40℃, and the stirring time was 24 hours. The polyacrylic acid concentration was 0.008%. The amphoteric surfactant was tetradecyl dimethylamine oxide with a mass percentage of 0.2%. The soaking temperature was 40℃ and the time was 40 min. The ultrasonic power was 200 W and the time was 20 min.

[0047] The final high-contamination-resistant radioisotope tracer microspheres consisted of a core and polyvinyl alcohol / iodine-131 layer accounting for 60% of the total mass, a chitosan layer accounting for 20%, and an outer mineralized shell accounting for 20%. The median particle size was 500 μm, the particle size distribution D10 / D90 was 3.0, and the true density was 1.1 g / cm³. 3 .

[0048] Comparative Example 1: Traditional Radioactive Isotope Tracing Microspheres Traditional radioactive isotope tracer microspheres were prepared using existing technology. The specific steps are as follows: Sodium iodide-131 was mixed evenly with polystyrene powder, and an appropriate amount of deionized water was added and stirred into a slurry. Iodide-131-containing polystyrene microspheres were obtained by spray drying. Specific parameters: polystyrene powder mesh size 100 mesh, sodium iodide-131 specific activity 50 mCi / L, water to powder mass ratio 1:1, spray drying inlet air temperature 120℃, outlet air temperature 60℃, atomization pressure 0.3 MPa. Microspheres with a particle size of 200-500 μm were obtained by sieving, without any surface modification or coating treatment.

[0049] Comparative Example 2: Single-layer chitosan-coated radioisotope tracer microspheres. Single-layer chitosan-coated radioisotope tracer microspheres were prepared using some of the techniques described in this invention. The specific steps are as follows: SS1. Prepare an aqueous solution of polyvinyl alcohol containing iodine-131 according to the S100 method of Example 3; SS2. Mix zeolite powder (unmodified hydrophobically) and polystyrene powder at a mass ratio of 3:7, and prepare radioisotope-containing microsphere cores using the S300 method of Example 3, but using unmodified ordinary zeolite powder. Microsphere cores with a particle size of 350 μm are obtained by sieving; SS3. Perform chitosan coating and solidification treatment on the microsphere cores according to the S200, S400, and S500 methods of Example 3; SS4. No outer mineralized shell construction or surface hydrophilic modification treatment is performed.

[0050] The resulting microspheres have only a three-layer structure: core-polyvinyl alcohol / iodine-131 layer-chitosan layer, without an outer mineralized shell.

[0051] Comparative Example 3: Multilayer Radioisotope Tracing Microspheres Without Hydrophobic Modification Multilayer radioisotope tracer microspheres without hydrophobic modification were prepared using some of the techniques of this invention. The specific steps are as follows: SS1-SS2. Prepare the corresponding solutions according to the S100 and S200 methods of Example 3; SS3. Prepare the core containing radioisotope microspheres using the S300 method of Example 3, but the zeolite powder is not hydrophobically modified and ordinary zeolite powder is used directly; SS4-SS5. Coat and solidify with chitosan according to the S400 and S500 methods of Example 3; SS6. Construct the outer mineralized shell according to the S600 method of Example 3, but without adding disodium hydrogen phosphate crystal form regulator or hydrophilic modification treatment with zwitterionic surfactants.

[0052] The resulting microspheres have a complete four-layer structure, but the core zeolite is not hydrophobically modified, the outer mineralized shell is ordinary calcite-type calcium carbonate, and the surface is not hydrophilically modified.

[0053] Performance test comparison: In order to verify the relevant technical effects of the technical solution of the present invention, the present invention also conducted the following performance tests on the microspheres prepared in Examples 2-4 and Comparative Examples 1-3 and made subsequent performance comparisons: Apparent static contact angle test: Using a contact angle measuring instrument, the microspheres were pressed into a flat surface, and the static contact angle of deionized water on the surface of the microspheres was measured at 25°C. Each sample was tested 5 times and the average value was taken.

[0054] Oil stain resistance test: Prepare simulated oil-contaminated injection water (mineralization 100 g / L, crude oil 10 mg / L, partially hydrolyzed polyacrylamide 1500 mg / L), add 1.0 g microspheres to 50 mL of simulated contaminated water, stir and circulate for 4 hours at 25℃ and 150 rpm, take samples every 1 hour, rinse with deionized water, dry and weigh, and calculate the percentage increase in oil stain adhesion.

[0055] Radionuclide immobilization stability test: 0.5 g microspheres were placed in 100 mL of simulated injection water with a mineralization of 150 g / L and soaked for 30 days under constant temperature oscillation at 90℃. Water samples were taken periodically to determine the leaching concentration of iodine-131 and the cumulative leaching rate was calculated.

[0056] High-temperature and high-mineralization stability test: Microspheres were placed in high-mineralization water with a mineralization of 200 g / L and treated in a high-temperature autoclave at 120℃ for 72 hours. After removal, the surface morphology changes of the microspheres were observed, and the shell cracking rate and exfoliation rate were measured. The microstructure of the microsphere surface was observed using scanning electron microscopy (SEM).

[0057] Wellbore migration simulation experiment: A simulated wellbore device (a vertical tubing with an inner diameter of 25 mm and a length of 2 m, with a crude oil contamination point set at 1 m) was constructed. The injection flow rate was the simulated injection water flow rate (0.5 m / s). The microsphere suspension was injected from the top, and the retention rate and settling velocity of the microspheres at the oil contamination point were measured.

[0058] Tracer detection sensitivity test: The radioactivity count rate of microsphere suspensions at different concentrations was measured using a gamma-ray detector, a concentration-count rate standard curve was established, and the limit of detection was calculated.

[0059] Batch consistency test: Three batches of microspheres were prepared using the same process parameters (for Examples 2-4 only). Key indicators such as particle size distribution, contact angle, oil adhesion rate, and radioactivity of each batch of microspheres were measured, and the inter-batch coefficient of variation (CV%) was calculated.

[0060] Table 1 Summary of Test Results Regarding oil resistance, the apparent static contact angles of Examples 2-4 were all less than 20°, significantly lower than those of Comparative Examples 1-3, indicating that the surface of the microspheres of the present invention possesses excellent superhydrophilicity. The increase in oil adhesion after 4 hours did not exceed 5%, significantly lower than the comparative examples (Comparative Example 1 reached 18.6%), proving that the multilayer composite structure and surface modification technology of the present invention can effectively block oil adhesion.

[0061] Regarding the stability of radionuclides under immobilization, the cumulative iodine-131 leaching rate after 30 days in Examples 2-4 was less than 2.5%, while that in Comparative Example 1 was as high as 15.7%, and that in Comparative Examples 2 and 3 were 4.2% and 2.9%, respectively. This indicates that the multiple protection mechanism of the present invention, which combines zeolite / polystyrene composite core with polyvinyl alcohol immobilization, chitosan sealing, and mineralized shell barrier, can significantly improve the stability of radionuclides under immobilization.

[0062] Regarding high-temperature and high-mineralization stability, after 72 hours of treatment at 120℃ and 200g / L mineralization, Examples 2-4 showed that the shell cracking rate and peeling rate were both less than 5%, while the cracking rates of Comparative Examples 2 and 3 reached 12.3% and 8.1%, respectively. This indicates that by optimizing the chitosan solidification conditions and mineralization shell construction process, the present invention enables the microspheres to maintain structural integrity even in extreme reservoir environments.

[0063] Regarding wellbore transport performance, Examples 2-4 showed a retention rate of less than 4% at a simulated wellbore depth of 1 meter in oil contamination, which was far lower than that of Comparative Example 1 (12.5%). This indicates that the present invention, by precisely controlling the microsphere particle size, density, and surface properties, enables the microspheres to have good flowability and reduces the risk of radioactive contamination.

[0064] Regarding tracer sensitivity, the limits of detection for Examples 2-4 are in the range of 0.03-0.08 mg / L, which is superior to Comparative Example 1 (0.12 mg / L), demonstrating that the radionuclide immobilization method of the present invention can reduce radiation dose while ensuring tracer sensitivity.

[0065] Regarding batch consistency, the inter-batch coefficients of variation (particle size, contact angle, and oil adhesion rate) of Examples 2-4 were all less than 5%, which was significantly better than that of Comparative Example 3 (5.6%-7.5%), indicating that the mother liquor recycling and reuse process of the mineralization system of the present invention can effectively ensure the batch stability of product quality.

[0066] The objectives of this invention have been fully and effectively achieved through the above embodiments. Those skilled in the art will understand that this invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments described above. Although the invention has been described with reference to what is currently considered the most practical and preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments, and any modifications that do not depart from the functional and structural principles of the invention will be included within the scope of the claims.

Claims

1. A method for preparing highly contamination-resistant radioactive isotope tracer microspheres, characterized in that, include: S100. Dissolve sodium iodide-131 and polyvinyl alcohol in deionized water to prepare a polyvinyl alcohol aqueous solution containing iodide-131 ions; S200. Add chitosan to an acidic aqueous solution and dissolve it under heating and stirring conditions to prepare an acidic chitosan aqueous solution; S300. Mix zeolite powder and polystyrene powder at a mass ratio of 2:8 to 4:6 and add them to a spheroidizing granulation device. During the spheroidizing process, spray the polyvinyl alcohol aqueous solution containing iodide-131 to form spheres and load the radioactive isotope into the spherical particles. Then, dry and sieve the obtained spherical particles to obtain radioactive isotope-containing microspheres with the required particle size; S400. The prepared microsphere cores are placed in a fluidized bed coating apparatus, and an acidic aqueous solution of chitosan is sprayed onto the microsphere cores in a fluidized suspension state to form a chitosan coating layer on the surface of the microsphere cores. The mass ratio of particles to chitosan solution is 1:5 to 1:

50. After spraying, the coated particles are dried and sieved to obtain chitosan-coated microspheres. S500. The chitosan-coated microspheres are immersed in ammonia water to neutralize and solidify the acidic chitosan layer into a stable shell. After washing and drying, microspheres with a solidified chitosan layer are obtained. S600. A first aqueous solution containing calcium chloride and polyacrylic acid and a second aqueous solution containing sodium carbonate are prepared. The second aqueous solution is added to the first aqueous solution and sodium hydroxide is added to adjust the alkalinity of the system. Under stirring conditions, the microspheres obtained in step S500 are added to the mineralization system at a liquid-solid volume ratio of 8:1 to 12:1 to react and form a calcium-containing inorganic-organic composite mineralized shell layer attached to the outside of the chitosan layer. After separation, drying and sieving, highly antifouling radioactive isotope tracer microspheres are obtained.

2. The method according to claim 1, characterized in that, In step S100, the degree of polymerization of the polyvinyl alcohol is 1700~2400, the degree of alcoholysis is 87~99%, the mass percentage concentration of the polyvinyl alcohol aqueous solution is controlled at 3~7%, and the specific activity of sodium iodide-131 is controlled at 10~100 mCi / L. In the preparation process, the polyvinyl alcohol is first dissolved in deionized water at 80~95 ℃. After the polyvinyl alcohol is completely dissolved, it is cooled to room temperature, and then sodium iodide-131 is added and stirred for 30~60 min until homogeneous.

3. The method according to claim 1 or 2, characterized in that, In step S100, non-radioactive sodium iodide is further added to the polyvinyl alcohol aqueous solution containing iodine-131 as a carrier iodine source, and the molar ratio of non-radioactive iodide ions to iodine-131 ions is controlled within the range of 10:1 to 5000:1, so that the microsphere core formed in the subsequent steps forms a solidified phase structure with non-radioactive iodide ions as the carrier and iodine-131 uniformly distributed inside.

4. The method according to claim 1, characterized in that, In step S200, the acidic aqueous solution is an acetic acid aqueous solution with a mass percentage concentration of 1-3%, the mass percentage concentration of chitosan in the chitosan acidic aqueous solution is 0.5-1.5%, the degree of deacetylation of chitosan is 75-95%, and the solution is stirred for 1-3 hours under heating conditions of 50-70 °C. After the chitosan is completely dissolved, it is cooled to room temperature for later use. During the heating and stirring process, the chitosan solution needs to be vacuum degassed to eliminate microbubbles inside the solution.

5. The method according to claim 1, characterized in that, In step S300, the zeolite powder is a crystalline aluminosilicate material with an ion-exchangeable pore structure, and its mesh size is controlled between 200 and 400 mesh; the polystyrene powder is a thermoplastic resin powder used as the organic framework for forming microsphere cores during the spheroidization process, and its mesh size is controlled between 80 and 150 mesh; the mass ratio of zeolite powder to polystyrene powder is controlled between 2:8 and 4:6; the amount of polyvinyl alcohol aqueous solution containing iodine-131 added is 0.8 to 1.3 times the total mass of the mixed powder, and the rotation speed of the spheroidizing granulation device is controlled between 15 and 30 rpm, the spheroidizing time is controlled between 20 and 60 min, the air volume is controlled between 5 and 15 ml / min, and the rate of spraying the polyvinyl alcohol aqueous solution containing iodine-131 during the spheroidizing granulation process is controlled so that the mixed powder is wetted but not sticky, and the drying process adopts a step-by-step heating method, first drying at a low temperature of 45 to 55°C for 2 to 4 hours, and then heating to 70 to 90°C for medium-temperature drying for 100 to 150 hours. After min, radioactive isotope-containing microspheres with a particle size of 10~2000 μm were finally obtained by sieving.

6. The method according to claim 1, characterized in that, In step S400, the fluidized bed coating device adopts a bottom-up air supply structure. The flow rate of the air is adjusted to a range that allows the microsphere core particles to form a uniform fluidized suspension state while avoiding collision and breakage. The air intake is adjusted so that the height of the fluidized bed is 1 / 2 to 2 / 3 of the total height of the drying chamber. The chitosan acidic aqueous solution is atomized and sprayed into the fluidized bed through a top or bottom spray gun. The atomization pressure is set to 0.15-0.25 MPa, the spray droplet size is controlled at 20-150 μm, and the spraying rate is adjusted to match the fluidization state and ensure uniform deposition of chitosan on the surface of the microsphere core. The spraying process adopts an intermittent spraying method, stopping spraying after every 5-10 minutes and continuing fluidized drying for 2-5 minutes. This cycle is repeated until the preset coating thickness is achieved. During the coating process, the air intake temperature is controlled at 80-100 ℃, and the material temperature is maintained at 70-90 ℃. At ℃, the moisture in chitosan gradually evaporates and eventually forms chitosan-coated microspheres with a continuous, flat surface that do not agglomerate.

7. The method according to claim 1, characterized in that, In step S500, the mass percentage concentration of the ammonia water is 0.5-2%. The chitosan-coated microspheres are soaked in the ammonia water for 5-15 minutes at a temperature of 20-30°C. The soaking process is carried out with intermittent oscillation at a frequency of 80-120 times / minute to ensure that the ammonia water fully penetrates into the acidic layer of chitosan, so that it is fully neutralized and cross-linked and solidified to form a chitosan gel framework layer. Then, the solution is washed with deionized water until the pH value is close to neutral to remove residual free ammonia and soluble salts, and then dried at 70-90°C for 80-150 minutes.

8. The method according to claim 1, characterized in that, In step S600, the mass percentage concentration of calcium chloride in the first aqueous solution is 0.08~0.20%, and the mass percentage concentration of polyacrylic acid is 0.003~0.010%, and the concentration and mass ratio of calcium chloride to polyacrylic acid are controlled within a range that can form a stable calcium-containing organic complex and facilitate subsequent calcium carbonate deposition; the mass percentage concentration of sodium carbonate in the second aqueous solution is 0.08~0.20%; after mixing the first and second aqueous solutions, sodium hydroxide with a mass percentage concentration of 0.003-0.008% is added to adjust the alkalinity of the system and adjust the pH value of the system to 8.0~12.

0. Then, the microspheres obtained in step S500 are added to the mineralization system at a liquid-to-solid volume ratio of 8:1 to 12:1, and the mixture is heated for 20~40 minutes. Stirring at ℃ for 6-24 hours to maintain the mineralization reaction allows an inorganic-organic composite mineralized shell composed of calcium carbonate and calcium-polyacrylic acid composite structure to be generated in situ on the surface of the chitosan layer. After the mineralization reaction is completed, residual soluble inorganic salts and free polyacrylic acid are removed by solid-liquid separation, washing and drying, and finally highly resistant radioactive isotope tracer microspheres are obtained by sieving.

9. The method according to claim 1 or 8, characterized in that, In step S600, after the mineralization reaction is completed to form a calcium-containing inorganic-organic composite mineralized shell, the surface is further modified by hydrophilic modification: the mineralized microspheres are immersed in an aqueous solution containing a zwitterionic surfactant, wherein the zwitterionic surfactant is selected from at least one of dodecyl dimethyl betaine and tetradecyl dimethylamine oxide, and its mass percentage concentration is controlled at 0.05~0.2%, the immersion temperature is 30~40 ℃, the immersion time is 20~40 min, and the immersion process is ultrasonically assisted, with the ultrasonic power controlled at 100~200 W and the ultrasonic time being 10~20 min. Utilizing the calcium ion sites or residual active groups on the surface of the mineralized shell, the zwitterionic surfactant molecules are formed on the surface of the mineralized shell through electrostatic adsorption or surface grafting polymerization, thus constructing a nano-thickness strong hydration layer on the outer layer of the microspheres.

10. The method according to claim 1, characterized in that, In step S600, after the mineralization reaction is completed, the mineralization system is filtered and separated and the mother liquor is recovered. By detecting the concentration of calcium ions and carbonate ions in the mother liquor and supplementing with calcium chloride, sodium carbonate and sodium hydroxide solutions of corresponding mass fractions, the ionic strength and pH of the mineralization system are kept within the preset range. This ensures that the same mineralization pool can be continuously used for the construction of multiple batches of outer mineralization shells, guaranteeing batch-to-batch consistency in the thickness and surface properties of the outer mineralization shell of the highly fouling-resistant radioisotope tracer microspheres obtained from different batches.

11. The method according to claim 1, characterized in that, By comprehensively controlling the solid addition amount, curing time, and drying conditions of the radioactive isotope-containing microsphere core, chitosan coating layer, and outer mineralized shell in steps S300~S600, the finally obtained highly antifouling radioactive isotope tracer microspheres have a multi-layered concentric shell structure in the radial direction, consisting of a zeolite / polystyrene composite core, a polyvinyl alcohol / iodine-131 layer, a cured chitosan layer, and a calcium-containing inorganic-organic composite mineralized shell layer, from the inside out. The core and polyvinyl alcohol / iodine-131 layer account for 60~85% of the total mass of the microspheres, the chitosan layer accounts for 5~20% of the total mass of the microspheres, and the outer mineralized shell accounts for 5~20% of the total mass of the microspheres, forming a multi-layered synergistic antifouling and stable load structure.

12. The method according to claim 1, characterized in that, In steps S400 and S600, by adjusting the solid content of the chitosan solution, the spraying rate, the mineralization reaction time, and the molar ratio of calcium source to carbonate in the mineralization system, the apparent static contact angle of the finally obtained high-fouling-resistant radioisotope tracer microspheres in simulated oil- and polymer-contaminated injected water is not greater than 60°, and after repeated cycles of contact with oil-containing solution under preset stirring and shearing conditions, the increase in the amount of oil adhering to the surface of the microspheres relative to the initial mass of the microspheres does not exceed 5%.

13. The method according to claim 1, characterized in that, By comprehensively adjusting the mass ratio of zeolite to polystyrene, the spheroidizing and drying conditions, and the deposition amount of each shell material in steps S300-S600, the median particle size of the finally obtained high-fouling-resistant radioisotope tracer microspheres is controlled within 50-300 μm, the ratio of D10 to D90 of the particle size distribution is not greater than 3.0, and the true density of the microspheres is controlled within 0.9-1.2 g / cm³. 3 .

14. The method according to claim 1, characterized in that, By comprehensively adjusting the ammonia concentration, chitosan solid content, mineralization reaction pH, and mineralization time in steps S500 and S600, the crosslinking density of the solidified chitosan layer is matched with the density of the outer mineralized shell. This ensures that the resulting highly antifouling radioisotope tracer microspheres do not experience significant cracking, peeling, or swelling instability when injected into a high-temperature, high-mineralization water environment at a temperature range of 80–120 °C and a mineralization degree of 50–200 g / L.

15. A highly contamination-resistant radioactive isotope tracer microsphere, characterized in that, The preparation method is based on the preparation method of highly antifouling radioisotope tracer microspheres according to any one of claims 1 to 14.

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