PESA / N-CQDs scale inhibitor as well as preparation method and application thereof

Abstract

The invention discloses a PESA / N-CQDs scale inhibitor and a preparation method and application thereof.The preparation method comprises the steps that citric acid, urea and a polyepoxysuccinic acid salt solution serve as raw materials, nitrogen-doped carbon quantum dots are prepared through a hydrothermal method (150-170 DEG C, 3-5 hours), then polyepoxysuccinic acid is obtained through precipitation and drying treatment, and the PESA / N-CQDs scale inhibitor is obtained. And finally, mixing the nitrogen-doped carbon quantum dots with polyepoxysuccinic acid, adjusting the pH value to 7-8, stirring and reacting for 20-28 hours at the temperature of 75-85 DEG C, and precipitating, washing and drying to obtain the PESA / N-CQDs scale inhibitor. The method is simple, convenient and controllable in process, environment-friendly, good in product dispersity, capable of showing excellent scale inhibition efficiency after being added in a trace amount, suitable for scale inhibition treatment of various scale-containing systems such as industrial circulating water and oilfield production water, and good in application prospect.

Description

A PESA / N-CQDs scale inhibitor, its preparation method and application Technical Field

[0001] This application relates to the field of scale inhibitor technology, and in particular to a PESA / N-CQDs scale inhibitor, its preparation method and application. Background Technology

[0002] As my country's oilfield development gradually enters the high water-cut stage, the produced water from the formation is rich in Ca²⁺. + Mg² + CO3² - Various high-concentration scale-forming ions are present. During produced water reuse and oil and gas extraction, scale-forming ions are easily precipitated and form scale due to changes in temperature, pressure, and pH. This not only clogs rock pores and reduces formation permeability, but also causes a decrease in pipeline heat transfer efficiency, increased equipment wear, and serious energy losses and production safety hazards. Therefore, scale inhibition treatment has become a key link in the operation of oilfield production and industrial circulating water systems.

[0003] Currently, adding scale inhibitors is the mainstream technical means to prevent and control scaling problems. Among them, carbon quantum dot scale inhibitors have attracted widespread attention due to their advantages such as readily available raw materials, abundant surface active groups, and good environmental compatibility. However, existing carbon quantum dot scale inhibitors generally suffer from the core bottleneck of excessive dosage and insufficient scale inhibition efficiency. To improve their performance, current research often adopts a modification strategy of simultaneous reaction between polymer precursors and carbon quantum dots, but this faces the problems of complex reaction pathways and difficulty in accurately controlling the degree of polymer polymerization and quantum dot loading. In addition, polyepoxysuccinic acid, as a mature and environmentally friendly scale inhibitor polymer, has advantages such as high functional group density and wide scale inhibition range. However, how to achieve precise compounding with carbon quantum dots through a clear reaction pathway to construct a high-efficiency scale inhibition system with synergistic performance has not yet formed a mature technical solution.

[0004] Therefore, how to overcome the performance and process bottlenecks of existing scale inhibitors and meet the high-efficiency scale inhibition requirements of oilfields and industrial scale-containing systems is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] This application provides a PESA / N-CQDs scale inhibitor, its preparation method, and its application, which solves the problem that existing scale inhibitors have performance and process bottlenecks that cannot meet the high-efficiency scale inhibition requirements of oilfield and industrial scale-containing systems.

[0006] In one aspect, embodiments of this application provide a method for preparing PESA / N-CQDs scale inhibitors, comprising: using a hydrothermal method, dissolving citric acid and urea in deionized water; after complete dissolution, transferring the deionized aqueous solution containing citric acid and urea to a polytetrafluoroethylene-lined autoclave; reacting at a constant temperature of 150-170°C for 3-5 hours; after the reaction, filtering the reaction product in the autoclave through a microporous membrane to remove impurities, then dialyzing and purifying it using a dialysis bag for 10-14 hours; finally, drying and grinding the purified product at 65-75°C to obtain nitrogen-doped carbon quantum dots; adjusting the pH of the polyepoxysuccinate solution to 2.0-3.0 with concentrated hydrochloric acid, then adding it to 3 times its volume of ethanol solution for precipitation treatment to obtain a white viscous precipitate; and subjecting the white viscous precipitate to vacuum treatment. The mixture is filtered and washed with ethanol solution, then dried in a vacuum at 75-85℃ for 10-14 hours to obtain polyepoxysuccinic acid. The polyepoxysuccinic acid is dissolved in deionized water to obtain a clear solution. Nitrogen-doped carbon quantum dots are added to the clear solution and stirred to dissolve, resulting in a mixture. The pH value is adjusted to 7-8 by adding 1 mol / L NaOH solution to the mixture. The mixture is then stirred continuously at 75-85℃ for 20-28 hours. After the reaction is completed, the mixture is cooled to room temperature to obtain a filtrate. Large particulate impurities in the filtrate are removed by filtration. Anhydrous ethanol is added to the filtrate and allowed to stand for 10-14 hours to precipitate. The precipitate is collected by filtration and washed with anhydrous ethanol. Finally, the precipitate is dried at 75-85℃ to obtain PESA / N-CQDs scale inhibitor.

[0007] In conjunction with the first aspect, in one possible implementation, the mass ratio of the citric acid, the urea, and the deionized water is 1-3:1.5-2.5:40-60.

[0008] In conjunction with the first aspect, in one possible implementation, when preparing nitrogen-doped carbon quantum dots by the hydrothermal method, the heating rate of the autoclave is 5-8℃ / min, and the particle size of the nitrogen-doped carbon quantum dots is 2-8nm.

[0009] In conjunction with the first aspect, in one possible implementation, the dialysis bag has a molecular weight cutoff of 500-1000 Da, and the temperature of the distilled water is maintained at 20-25°C during dialysis.

[0010] In conjunction with the first aspect, in one possible implementation, the mass concentration of the polyepoxysuccinate solution is 30-40%, the addition rate of anhydrous ethanol is 5-10 mL / min, and the water content of the white viscous precipitate is ≤5%.

[0011] In conjunction with the first aspect, in one possible implementation, the mass ratio of the polyepoxysuccinic acid to the nitrogen-doped carbon quantum dots is 8-12:1, and the mass concentration of the polyepoxysuccinic acid in the mixture is 15-25%.

[0012] In conjunction with the first aspect, in one possible implementation, the stirring speed of the mixture is 300-500 rpm, and the rate of adding NaOH solution is 0.5-1 mL / min.

[0013] In conjunction with the first aspect, in one possible implementation, the vacuum degree during the drying process of the solid product is -0.085 to -0.095 MPa, and the drying process includes first raising the temperature to 50°C at 3°C / min and holding it for 2 hours, and then raising the temperature to 75-85°C for continuous drying.

[0014] Secondly, embodiments of this application provide a PESA / N-CQDs scale inhibitor prepared using the preparation method described in the first aspect or any possible implementation of the first aspect, comprising: the PESA / N-CQDs scale inhibitor is a green particle; the PESA / N-CQDs scale inhibitor uses nitrogen-doped carbon quantum dots as a substrate and forms a composite system by covalent bonding with polyepoxysuccinic acid through amide bonds; the scale inhibitor has a predominantly spherical morphology with a particle size distribution of 1-6 nm, a crystal interplanar spacing of 0.22-0.26 nm, good dispersibility, and no significant agglomeration; the scale inhibitor is composed of four elements: C, N, O, and H, and its surface is rich in active functional groups such as carboxyl groups, hydroxyl groups, and amide groups.

[0015] Thirdly, embodiments of this application provide an application of the PESA / N-CQDs scale inhibitor prepared using the preparation method described in the first aspect or any possible implementation of the first aspect, including: the PESA / N-CQDs scale inhibitor is suitable for scale inhibition treatment of different scale-containing systems in industrial circulating water and production water during oil and gas extraction; when the dosage of the scale inhibitor is 15-25 ppm, the scale inhibition rate for calcium carbonate is ≥90%, and the core permeability retention rate is ≥78%.

[0016] One or more technical solutions provided in this application embodiment have at least the following technical effects or advantages: This application embodiment uses citric acid, urea, and polyepoxysuccinate solution as raw materials. First, nitrogen-doped carbon quantum dots are prepared via a hydrothermal method (150-170℃, 3-5 hours). Then, after precipitation and drying, polyepoxysuccinate is obtained. Finally, the nitrogen-doped carbon quantum dots and polyepoxysuccinate are mixed and the pH is adjusted to 7-8. The mixture is stirred and reacted at 75-85℃ for 20-28 hours. After precipitation, washing, and drying, PESA / N-CQDs scale inhibitor is obtained. This application has a simple and controllable process, is environmentally friendly, and produces products with good dispersibility. Even a small amount of product can exhibit excellent scale inhibition performance. It is suitable for scale inhibition treatment in various scale-containing systems such as industrial circulating water and oilfield production water, and has good application prospects. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 is a TEM characterization diagram of the PESA / N-CQDs scale inhibitor provided in the embodiments of this application; Figure 2 is an XPS characterization diagram of the PESA / N-CQDs scale inhibitor provided in the embodiments of this application; Figure 3 is an FTIR characterization diagram of the PESA / N-CQDs scale inhibitor provided in the embodiments of this application; Figure 4 is a scale inhibition efficiency diagram of different PESA:N-CQDs ratios provided in the embodiments of this application; Figure 5 is a scale inhibition efficiency diagram of PESA and PESA / N-CQDs at different dosage concentrations provided in the embodiments of this application; Figure 6 is a dynamic scale inhibition effect evaluation diagram of oilfield water samples provided in the embodiments of this application. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] The following description of some technologies involved in the embodiments of this application is provided to aid understanding and should be considered merely exemplary. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. Similarly, for clarity and brevity, some descriptions of well-known functions and structures are omitted in the following description.

[0021] Example 1: Preparation of PESA / N-CQDs scale inhibitor.

[0022] Raw material formula.

[0023] Raw materials for the preparation of nitrogen-doped carbon quantum dots (N-CQDs): 2g citric acid (1mmol), 1.9g urea (3mmol), and 50mL deionized water.

[0024] Raw materials for the preparation of polyepoxysuccinic acid (PESA): 20 mL of polyepoxysuccinate solution, concentrated hydrochloric acid (for pH adjustment), and 60 mL of ethanol.

[0025] The composite raw materials for PESA / N-CQDs scale inhibitor are: 0.60g PESA, 0.06g N-CQDs, 10mL deionized water, 1mol / L NaOH solution (for pH adjustment), and 30mL anhydrous ethanol.

[0026] 1.2 Preparation steps.

[0027] Step 1: Preparation of N-CQDs.

[0028] Weigh 2g of citric acid and 1.9g of urea, add 50mL of deionized water and stir until completely dissolved. Transfer the mixture to a 100mL high-pressure autoclave lined with polytetrafluoroethylene and react at 160℃ for 4 hours. After the reaction, filter through a 0.22μm microporous membrane to remove impurities, and then dialyze using a dialysis bag with a molecular weight cutoff of 1000Da for 12 hours (changing the distilled water every 3 hours). Finally, dry and grind at 70℃ to obtain blue powdered N-CQDs, which are then sealed and stored in a desiccator for later use.

[0029] Step 2: Preparation of PESA.

[0030] Take 20 mL of polyepoxysuccinate solution, adjust the pH to 2.5 with concentrated hydrochloric acid, add 60 mL of ethanol at a volume ratio of 1:3 for precipitation, stir until a white viscous precipitate is formed, let stand for 10 min, then filter under vacuum, wash the precipitate 3-4 times with ethanol, and dry it in an 80℃ vacuum drying oven for 12 hours to obtain white powdered PESA.

[0031] Step 3: Preparation of PESA / N-CQDs scale inhibitor.

[0032] Mix 0.60g PESA with 10mL deionized water and stir to form a clear solution. Add 0.06g N-CQDs and continue stirring to dissolve. Adjust the pH of the mixture to 7-8 by adding 1mol / L NaOH solution dropwise. Stir continuously at 80℃ for 24 hours. After the reaction is complete, cool to room temperature and remove large particulate impurities by conventional filtration. Add 30mL anhydrous ethanol to the filtrate and let it stand for 12 hours to precipitate. Collect the solid product by filtration, wash 3-4 times with anhydrous ethanol, and finally dry at 80℃ to obtain a green solid PESA / N-CQDs scale inhibitor.

[0033] 1.3 Performance and characterization tests.

[0034] Appearance: Green solid powder with no obvious agglomeration.

[0035] Characterization results: As shown in Figure 1, Figure 1 is a TEM characterization diagram of the PESA / N-CQDs scale inhibitor provided in the embodiments of this application: the particle size distribution is between 1.5-5.5 nm, the morphology is mainly circular, the interplanar spacing is 0.24 nm, and the dispersibility is good.

[0036] As shown in Figure 2, the XPS characterization of the PESA / N-CQDs scale inhibitor provided in this embodiment of the application is as follows: the C1s peak appears at 285.7 eV, the N1s peak appears at 397.61 eV, and the O1s peak appears at 529.57 eV. After Gaussian fitting of the high-resolution C1s spectrum of PESA / N-CQDs, it can be decomposed into three characteristic peaks: the characteristic peak at 284.8 eV corresponds to the CC / C=C bond, the characteristic peak at 286.7 eV corresponds to the CO / CN bond, and the characteristic peak at 288.3 eV corresponds to the C=O bond. The high-resolution O1s spectrum shows two characteristic peaks with binding energies of 527.88 eV and 532.3 eV, respectively, corresponding to the C=O bond and the C-OH / COC bond. The high-resolution N1s spectrum, after fitting, yielded three characteristic peaks: 396.35 eV corresponding to a CNC bond, 396.84 eV corresponding to a CNH bond, and 399.96 eV corresponding to an NH bond. Furthermore, the characteristic sodium signal appearing at a binding energy of 497.33 eV in the full spectrum can be attributed to residual sodium hydroxide added during the synthesis process.

[0037] As shown in Figure 3, Figure 3 is the FTIR characterization diagram of the PESA / N-CQDs scale inhibitor provided in the embodiments of this application: 3433.24 cm⁻¹ - At position ¹, there is an absorption peak for -OH or NH in -COOH, at 1615.73 cm⁻¹. - A -C=O stretching vibration peak is observed at position ¹, at 1397.20 cm⁻¹. - The presence of an amide group-CN bond absorption peak at position ¹ confirms the successful grafting of PESA with N-CQDs.

[0038] Scale inhibition performance: Scale inhibition performance is achieved using oilfield production water (Na₂O₃). + +K + 11.40 g / L, Ca² + (e.g., 0.70 g / L), when the dosage is 20 ppm, the scale inhibition rate of CaCO3 reaches 92.39%.

[0039] Reservoir adaptability: When using quartz sand and epoxy resin bonded artificial cores (permeability 25.00 mD, porosity 24.08%), with an addition of 20 ppm, the core permeability retention rate reaches 80.02%, which can prevent scaling of containers and pipelines as well as reservoir blockage.

[0040] Example 2: Effect of different PESA to N-CQDs ratios on scale inhibition performance.

[0041] 2.1 Variable settings.

[0042] The amount of N-CQDs was fixed at 0.06g, and the amount of PESA was adjusted to 0.2g, 0.4g, 0.6g and 0.8g respectively. The amount of other raw materials and the preparation steps were the same as in Example 1.

[0043] 2.2 Performance test results.

[0044] Under the condition of a dosage of 20 ppm, with a fixed amount of nitrogen-doped carbon quantum dots (PESA) of 0.06 g, adjusting the amount of polyepoxysuccinic acid (PESA) to change the ratio of PESA to N-CQDs resulted in significant changes in scale inhibition performance. When the amount of PESA was 0.2 g, the mass ratio of PESA to N-CQDs was 10:3, and the scale inhibition rate was only 65.72%. As the amount of PESA increased to 0.4 g, the mass ratio became 20:3, and the scale inhibition rate increased to 82.45%. When the amount of PESA was 0.6 g and the mass ratio reached 10:1 (30:3), the scale inhibition rate jumped significantly to 92.39%. Further increasing the amount of PESA to 0.8 g, the mass ratio was 40:3, and the scale inhibition rate only increased slightly to 93.15%, with the increase becoming gradual. A mass ratio of PESA to N-CQDs of 10:1 already achieved excellent scale inhibition effect, which is the optimal ratio for the synergistic effect of the two.

[0045] As shown in Figure 4, the scale inhibition efficiency is shown under different PESA:N-CQDs ratios provided in the embodiments of this application. When the mass ratio of PESA to N-CQDs is 10:1 (0.6g PESA + 0.06g N-CQDs), the scale inhibition rate has reached more than 92%. Further increasing the amount of PESA will result in a slight increase in the scale inhibition rate. Therefore, the optimal ratio is determined to be 10:1.

[0046] Example 3: Effect of different dosages on scale inhibition performance.

[0047] 3.1 Variable settings.

[0048] The scale inhibitor was prepared using the optimal formulation of Example 1 (PESA 0.6g + N-CQDs 0.06g), with dosages of 5ppm, 10ppm, 15ppm, 20ppm, 25ppm, and 50ppm, and the remaining experimental conditions were the same as those in the static scale inhibition evaluation of Example 1.

[0049] 3.2 Performance test results.

[0050] Scale inhibitors were prepared using an optimal formulation of PESA to N-CQDs at a mass ratio of 10:1, and different dosages were set up for comparison with PESA alone. When the dosage is 5 ppm, the scale inhibition rate of PESA / N-CQDs scale inhibitor is 48.26%, while that of PESA alone is 35.18%. When the dosage is increased to 10 ppm, the scale inhibition rates of the two reach 72.58% and 58.34% respectively, and the gap widens further. When the dosage is 15 ppm, the scale inhibition rate of PESA / N-CQDs rises to 86.71%, while that of PESA alone is 70.45%. When the dosage reaches 20 ppm, the scale inhibition rate of PESA / N-CQDs is as high as 92.39%, while that of PESA alone is only 75.62%. When the dosage is 25 ppm, the scale inhibition rate of PESA / N-CQDs continues to increase to 95.12%, while that of PESA alone is 78.93%. When the dosage is increased to 50 ppm, PESA / N-CQDs achieves 100% complete scale inhibition, while the scale inhibition rate of PESA alone is 88.76%. Overall, PESA / N-CQDs scale inhibitors consistently outperform PESA alone in scale inhibition performance, and achieve highly efficient scale inhibition at a dosage of 20 ppm, demonstrating the core advantage of high efficiency with minimal dosage.

[0051] As shown in Figure 5, the scale inhibition efficiency of PESA and PESA / N-CQDs at different dosage concentrations provided in the embodiments of this application is shown. The scale inhibition performance of PESA / N-CQDs is always better than that of PESA alone. The scale inhibition rate reaches 92.39% when the dosage is 20ppm and complete scale inhibition is achieved at 50ppm, demonstrating the core advantage of high efficiency with minimal dosage.

[0052] Example 4: Evaluation of the scale inhibition performance of core flow dynamics.

[0053] 4.1 Experimental conditions.

[0054] The scale inhibitor was prepared using the optimal formulation of Example 1. The core parameters were the same as in Example 1 (permeability 25.00 mD, length 4.230 cm, radius 1.25 cm). The displacing fluid was oilfield production water. The scale inhibitor dosages were 20 ppm and 25 ppm, respectively. A blank group (without scale inhibitor) and a single PESA group (20 ppm) were set up as controls. The displacing flow rate was 2 cm³ / min, and the displacing was carried out at a constant temperature of 80℃ to 100 PV.

[0055] 4.2 Performance test results.

[0056] Using quartz sand and epoxy resin bonded artificial cores (gas permeability 25.00 mD, length 4.230 cm, radius 1.25 cm, porosity 24.08%) as the research object, and oilfield production water as the displacement fluid, the dynamic scale inhibition effects of different systems were compared under constant temperature of 80℃ and displacement flow rate of 2 cm³ / min. The core permeability retention rate of the blank group (without any scale inhibitor) was only 47.0%, while the reservoir damage rate was as high as 53.0%, indicating severe scaling damage. After adding 20 ppm of PESA alone, the permeability retention rate only slightly increased to 48.0%, and the reservoir damage rate was still 52.0%, indicating limited scale inhibition and anti-clogging effects. However, when 20 ppm of PESA / N-CQDs scale inhibitor was added, the core permeability retention rate increased significantly to 80.02%, and the reservoir damage rate decreased to 19.98%. When the dosage of PESA / N-CQDs was increased to 25 ppm, the permeability retention rate further increased to 82.2%, and the reservoir damage rate decreased to 17.8%, fully meeting the technical requirement of ≤20% reservoir damage rate in oilfield water injection operations.

[0057] As shown in Figure 6, Figure 6 is an evaluation diagram of the dynamic scale inhibition effect of oilfield water samples provided in the embodiments of this application. The permeability retention rate of the PESA / N-CQDs group is significantly better than that of the blank group and the single PESA group. The damage rate is only 19.8% when the dosage is 20ppm, which meets the requirements of oilfield water injection (≤20%), and the dynamic scale inhibition effect is excellent.

[0058] Example 5: Orthogonal experiment for process parameter optimization.

[0059] To verify the impact of core process parameters, an L9(3³) orthogonal experiment was conducted with dialysis time, reaction temperature (PESA and N-CQDs composite stage), and pH value as variables. The evaluation index was the scale inhibition rate at a dosage of 20 ppm.

[0060] An orthogonal experiment was conducted to optimize process parameters by considering dialysis time, temperature of the combined reaction of PESA and N-CQDs, and pH value of the combined reaction as influencing factors, and using scale inhibition rate at a dosage of 20 ppm as the evaluation index. When the dialysis time was 10 hours, the scale inhibition rate was 88.6% at a combined reaction temperature of 75℃ and pH = 7. The scale inhibition rate increased to 91.2% at 80℃ and pH = 7.5, and reached 89.5% at 85℃ and pH = 8. When the dialysis time was extended to 12 hours, the scale inhibition rate was 90.8% at 75℃ and pH = 7.5. The scale inhibition rate reached its maximum value of 92.39% at 80℃ and pH = 8, and reached 90.1% at 85℃ and pH = 7. When the dialysis time was 14 hours, the scale inhibition rate was below 91% for all temperature and pH combinations, with 89.3% at 75℃ and pH = 8, 90.7% at 80℃ and pH = 7, and 88.9% at 85℃ and pH = 7.5. In summary, the combination of parameters—dialysis time of 12 hours, combined reaction temperature of 80℃, and pH value of 7-8—enables the scale inhibitor to achieve optimal scale inhibition performance, consistent with the baseline process parameters.

[0061] The results of the orthogonal experiment show that the optimal combination of process parameters is: dialysis time of 12h, composite reaction temperature of 80℃, and pH value of 7-8, which is consistent with the baseline process of Example 1. At this time, the scale inhibition rate reaches the maximum value of 92.39%.

[0062] Comparative examples (performance comparisons deviating from the limitations of this application).

[0063] Comparative Example 1: Preparation by simultaneous reaction method (not synthesis followed by modification).

[0064] Citric acid, urea, and polyepoxysuccinate precursor were simultaneously added to an autoclave for a hydrothermal reaction. The amounts of other raw materials were the same as in Example 1. N-CQDs and PESA were not prepared separately. The results showed that the product exhibited severe agglomeration (particle size 10-20 nm), with a scale inhibition rate of only 72.3% at a dosage of 20 ppm and a core permeability retention rate of 55.8%. Due to the complex reaction pathway, the degree of polymerization and quantum dot loading could not be precisely controlled, resulting in a significant decrease in performance.

[0065] Comparative Example 2: Missing N-CQDs (single PESA system).

[0066] When PESA was prepared alone (same as step 2 in Example 1) without the addition of N-CQDs, the scale inhibition rate was 75.62% and the core permeability retention rate was 48.0% at a dosage of 20 ppm. There was no functional synergy, and the scale inhibition and reservoir protection effects were poor.

[0067] Comparative Example 3: The pH value of the composite reaction deviated (pH=6).

[0068] During the preparation process, the pH value was adjusted to 6 during the PESA and N-CQDs composite stage, and the remaining steps were the same as in Example 1. The results showed that the amidation reaction was incomplete, the proportion of free PESA in the product was high, the scale inhibition rate was 81.5% at a dosage of 20 ppm, the core permeability retention rate was 68.3%, and the performance was lower than that of the system with a pH value of 7-8.

[0069] This application employs a core strategy of synthesis followed by modification to prepare N-CQDs and PESA stepwise and achieve precise grafting. By optimizing the raw material ratio (PESA:N-CQDs=10:1) and process parameters (dialysis for 12 hours, composite reaction at 80℃, pH 7-8), the resulting PESA / N-CQDs scale inhibitor possesses the following advantages: Structural characteristics: particle size 1.5-5.5nm, good dispersibility, and surface rich in active functional groups such as carboxyl, hydroxyl, and amide groups; Performance indicators: at a dosage of 20ppm, CaCO3 scale inhibition rate ≥92%, core permeability retention rate ≥80%, superior to existing single systems and simultaneous reaction systems; Process advantages: simple and controllable process, environmentally friendly, readily available raw materials, and potential for large-scale industrial production.

[0070] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for preparing a PESA / N-CQDs scale inhibitor, characterized in that, include: Citric acid and urea were dissolved in deionized water using a hydrothermal method. After complete dissolution, the deionized aqueous solution containing citric acid and urea was transferred to a polytetrafluoroethylene-lined autoclave and reacted at a constant temperature of 150-170℃ for 3-5 hours. After the reaction, the reaction product in the autoclave was filtered through a microporous membrane to remove impurities and then purified by dialysis using a dialysis bag for 10-14 hours. Finally, the purified product was dried and ground at 65-75℃ to obtain nitrogen-doped carbon quantum dots. The pH of the polyepoxysuccinate solution was adjusted to 2.0-3.0 with concentrated hydrochloric acid, and then precipitated by adding three times its volume of ethanol solution to obtain a white viscous precipitate. The white viscous precipitate was vacuum filtered, washed with ethanol solution, and then placed at 75-85℃. The polyepoxysuccinic acid is dried in a vacuum for 10-14 hours to obtain polyepoxysuccinic acid. The polyepoxysuccinic acid is dissolved in deionized water to obtain a clear solution. The nitrogen-doped carbon quantum dots are added to the clear solution and stirred to dissolve, resulting in a mixture. The pH value is adjusted to 7-8 by adding 1 mol / L NaOH solution to the mixture. The mixture is then stirred and reacted at 75-85°C for 20-28 hours. After the reaction is completed, the mixture is cooled to room temperature to obtain a filtrate. Large particulate impurities in the filtrate are removed by filtration. Anhydrous ethanol is added to the filtrate and allowed to stand for 10-14 hours to precipitate. The precipitate is collected by filtration and washed with anhydrous ethanol. Finally, the precipitate is dried at 75-85°C to obtain PESA / N-CQDs scale inhibitor.

2. The method according to claim 1, characterized in that, The mass ratio of the citric acid, the urea, and the deionized water is 1-3:1.5-2.5:40-60.

3. The method according to claim 1, characterized in that, When preparing nitrogen-doped carbon quantum dots by the hydrothermal method, the heating rate of the autoclave is 5-8℃ / min, and the particle size of the nitrogen-doped carbon quantum dots is 2-8nm.

4. The method according to claim 1, characterized in that, The dialysis bag has a molecular weight cutoff of 500-1000 Da, and the temperature of the distilled water is maintained at 20-25℃ during dialysis.

5. The method according to claim 1, characterized in that, The polyepoxysuccinate solution has a mass concentration of 30-40%, the anhydrous ethanol is added at a rate of 5-10 mL / min, and the white viscous precipitate has a water content of ≤5%.

6. The method according to claim 1, characterized in that, The mass ratio of the polyepoxysuccinic acid to the nitrogen-doped carbon quantum dots is 8-12:1, and the mass concentration of the polyepoxysuccinic acid in the mixture is 15-25%.

7. The method according to claim 1, characterized in that, The stirring speed of the mixture is 300-500 rpm, and the rate of adding NaOH solution is 0.5-1 mL / min.

8. The method according to claim 1, characterized in that, The vacuum degree during the drying process of the solid product is -0.085 to -0.095 MPa. The drying process includes first raising the temperature to 50°C at 3°C / min and holding it for 2 hours, and then raising the temperature to 75-85°C for continuous drying.

9. A PESA / N-CQDs scale inhibitor prepared by any one of the preparation methods described in claims 1-8, characterized in that, include: The PESA / N-CQDs scale inhibitor is a green particle. It is based on nitrogen-doped carbon quantum dots and covalently bonded to polyepoxysuccinic acid via amide bonds to form a composite system. The scale inhibitor is mainly spherical with a particle size distribution of 1-6 nm and a crystal interplanar spacing of 0.22-0.26 nm. It exhibits good dispersibility and no significant agglomeration. The scale inhibitor is composed of four elements: C, N, O, and H, and its surface is rich in active functional groups such as carboxyl, hydroxyl, and amide groups.

10. The application of a PESA / N-CQDs scale inhibitor prepared by any one of the preparation methods described in claims 1-8, characterized in that, include: The PESA / N-CQDs scale inhibitor is suitable for scale inhibition treatment of different scale-containing systems in industrial circulating water and production water during oil and gas extraction. When the dosage of the scale inhibitor is 15-25 ppm, the scale inhibition rate for calcium carbonate is ≥90%, and the core permeability retention rate is ≥78%.

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