Preparation method and tracing method of tracer agent

Abstract

The invention relates to the technical field of tracers, in particular to a tracer preparation method and a tracer method thereof, and the tracer preparation method comprises the following steps: (1) preparing a basic solution; (2) preparing a fluorophore: adding 27-54 mmol of 9-aminoacridine and 50-100 mL of absolute ethyl alcohol into a three-necked flask, heating and refluxing for 2-4 hours under the protection of nitrogen, cooling to room temperature, adding 34-91 mmol of acryloyl chloride, stirring and reacting for 1-2 hours at 0-5 DEG C, and after the reaction is finished, carrying out reduced pressure distillation to remove a solvent; (3) grafting reaction: dissolving the fluorophore intermediate obtained in the step (2) in 30-50 mL of dichloromethane, slowly dropwise adding into the basic solution obtained in the step (1), stirring and reacting for 4-6 hours at 20-30 DEG C, dialyzing and purifying for 3-5 days after the reaction is finished, and finally freeze-drying to obtain a powdery product; and (4) carrying out modification reaction to obtain a final tracer product.

Description

Technical Field

[0001] The present invention relates to the technical field of tracers, and particularly relates to a method for preparing a tracer and a tracing method thereof. Background Art

[0002] During the development of oil and gas fields, it is crucial to accurately evaluate reservoir characteristics and fluid dynamics. Traditional tracer technologies, such as radioactive isotopes and chemical tracers, face many challenges in application. Although radioactive isotopes have high sensitivity, they pose environmental safety hazards. Conventional chemical tracers, such as fluorescent dyes and inorganic salts, are relatively safe, but often have problems such as low detection sensitivity, poor stability, and easy adsorption by the reservoir, making it difficult to meet the requirements of long-term and accurate monitoring.

[0003] In recent years, nanomaterials have shown great potential in the field of oilfield tracing. However, current nano-tracers still have some limitations. For example, some nanoparticles have insufficient stability in the reservoir environment of high temperature and high pressure, or have too strong interaction with reservoir rocks, resulting in unsatisfactory tracing effects. In addition, the biocompatibility and environmental friendliness of some nanomaterials also need to be improved.

[0004] In view of this, there is an urgent need to develop a new type of tracer with high sensitivity, good stability, moderate adsorption, and environmental friendliness to meet the requirements of long-term and accurate monitoring of complex oil and gas reservoirs. Summary of the Invention

[0005] The present invention aims to solve the above technical problems and provides a fluorescent tracer modified with polyethylene glycol, a preparation method thereof, and an application thereof. Through a carefully designed molecular structure, this tracer realizes the synergistic effect of multiple functions.

[0006] The object of the present invention is to provide a method for preparing a tracer, including the following steps: (1) Prepare a basic solution: Dissolve 2.5 - 5.0 mmol of polyethylene glycol monomethyl ether in 80 - 90 mL of deionized water and stir evenly; (2) Prepare a fluorophore: Add 27 - 54 mmol of 9 - aminoacridine and 50 - 100 mL of absolute ethanol into a three-necked flask, heat under reflux for 2 - 4 hours under nitrogen protection, cool to room temperature, then add 34 - 91 mmol of acryloyl chloride, stir and react at 0 - 5 °C for 1 - 2 hours. After the reaction ends, remove the solvent by vacuum distillation; (3) Grafting reaction: Dissolve the fluorophore intermediate obtained in step (2) in 30 - 50 mL of dichloromethane, slowly drop it into the basic solution obtained in step (1), stir and react at 20 - 30 °C for 4 - 6 hours. After the reaction ends, perform dialysis purification for 3 - 5 days, change the external solution 4 - 6 times, and finally obtain a powdery product by freeze-drying; (4) Modification reaction: Dissolve 0.75 - 1.25 mmol of the powdery product obtained in step (3) in 20 - 30 mL of PBS buffer, add 0.5 - 1.5 mmol of N - succinimidyl - PEG - maleimide, stir and react at room temperature for 2 - 4 hours. After the reaction, perform dialysis purification and freeze - drying to obtain the final tracer product.

[0007] Preferably, the average molecular weight of the methoxypolyethylene glycol in step (1) is 4000.

[0008] Preferably, the dialysis purification in step (3) uses a dialysis membrane with a molecular weight cut - off value of 1000.

[0009] Preferably, the pH value of the PBS buffer in step (4) is 7.4.

[0010] Preferably, the average molecular weight of the N - succinimidyl - PEG - maleimide in step (4) is 2000.

[0011] A tracer method, comprising the following steps: (1) Dissolve 0.125 - 0.25 mmol of the tracer prepared by the method according to any one of claims 1 - 5 in 100 mL of physiological saline to make a tracer solution; (2) Before the fracturing operation, inject the tracer solution into the target reservoir through a high - pressure injection pump; (3) After the fracturing operation is completed, collect the back - flow liquid samples at preset time points; (4) Analyze the samples using a fluorescence spectrophotometer; (5) Draw a concentration - time curve according to the change of tracer concentration at different time points.

[0012] Preferably, the injection pressure of the high - pressure injection pump in step (2) is 20 - 40 MPa, and the injection rate is 0.5 - 2.0 mL / min.

[0013] Preferably, the preset time points in step (3) include 1 day, 7 days, 30 days, 90 days and 180 days after the fracturing operation is completed.

[0014] Preferably, the excitation wavelength of the fluorescence spectrophotometer in step (4) is set to 450 nm, and the emission wavelength is set to 520 nm.

[0015] Preferably, the tracer concentration is quantitatively analyzed by the standard curve method in step (4).

[0016] Through ingenious design and optimization, the present invention proposes a method for preparing a tracer and a tracing method, which have the following innovative points and beneficial effects: Firstly, polyethylene glycol monomethyl ether is used as the backbone, which not only provides excellent water solubility but also endows the tracer with good biocompatibility. The repeating ethoxy units (-CH2CH2O-) in the polyethylene glycol molecule form a unique helical structure that can effectively encapsulate water molecules, thus significantly improving the water solubility of the tracer. At the same time, this structure can also reduce the non-specific interaction between the tracer and biological macromolecules, reducing the potential impact on organisms.

[0017] Secondly, the introduction of a 9-aminoacridine-derived fluorophore is one of the key innovations of the present invention. This fluorophore not only has a high quantum yield and a large Stokes shift but also exhibits excellent photostability and thermal stability. Among them, the amino group on the acridine ring reacts with acryloyl chloride to form a stable amide bond, further enhancing the stability of the fluorophore. This design enables the tracer to maintain long-term fluorescence performance in a complex reservoir environment, providing the possibility for accurate monitoring.

[0018] Thirdly, the introduction of N-succinimidyl-PEG-maleimide is another innovation. The maleimide group can undergo a Michael addition reaction with thiols or amino groups on the surface of reservoir rocks to achieve controllable chemisorption. This design cleverly balances the migration ability and residence time of the tracer, enabling it to flow with formation fluids and retain on the rock surface for a long enough time for detection. At the same time, the introduction of the PEG segment further enhances the water solubility and biocompatibility of the tracer, forming a multi-functional synergistic molecular structure.

[0019] In addition, the preparation method of the present invention also embodies a number of innovations. For example, nitrogen protection is adopted during the synthesis of the fluorophore, effectively preventing the occurrence of oxidation side reactions and improving the purity and fluorescence performance of the product. The introduction of the dialysis purification step ensures the high purity of the final product and reduces potential interfering substances.

[0020] Based on the above design, the tracer of the present invention exhibits a number of beneficial effects: 1. High-sensitivity detection: The optimized fluorophore structure enables the tracer to be accurately detected even at ppb-level concentrations, greatly improving the monitoring accuracy.

[0021] 2. Long-term stability: Through molecular structure design and preparation process optimization, the tracer exhibits excellent stability in high-temperature and high-pressure reservoir environments and can achieve continuous monitoring for up to one year.

[0022] 3. Controllable Adsorbability: The introduction of maleimide groups enables controllable interaction between the tracer and reservoir rocks, ensuring effective tracing while avoiding signal loss caused by excessive adsorption.

[0023] 4. Environmental Friendliness: The molecular design based on polyethylene glycol endows the tracer with excellent biocompatibility, significantly reducing its potential impact on the environment.

[0024] 5. Broad-spectrum Applicability: By adjusting the molecular weight of polyethylene glycol, the tracer can adapt to reservoirs with different porosities, expanding its application range.

[0025] 6. Synergistic Enhancement: The ingenious combination of multifunctional groups not only optimizes various properties but also generates a synergistic effect beyond expectations, such as better reservoir adaptability and a higher signal-to-noise ratio.

[0026] In summary, through innovative molecular design and preparation methods, the present invention has successfully developed a new type of tracer with high sensitivity, good stability, moderate adsorbability, and environmental friendliness. This technological breakthrough provides a powerful tool for the long-term and accurate monitoring of complex oil and gas reservoirs and is expected to play an important role in optimizing oil and gas field development and enhancing oil recovery. Detailed Embodiments

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] Example 1: A Method for Preparing a Tracer and Its Tracing Method The method for preparing the tracer in this example includes the following steps: First, prepare the basic solution. Dissolve 2.5 mmol of methoxypolyethylene glycol (average molecular weight 4000) in 90 mL of deionized water and stir evenly to obtain the basic solution. In this step, methoxypolyethylene glycol as the backbone not only improves the water solubility of the tracer but also enhances its biocompatibility, thereby reducing the impact on the reservoir.

[0029] Secondly, prepare the fluorophore. Add 27 mmol of 9-aminoacridine and 50 mL of absolute ethanol into a 100 mL three-necked flask, and heat under reflux for 2 hours under nitrogen protection. After cooling to room temperature, add 34 mmol of acryloyl chloride and stir the reaction at 0 °C for 1 hour. After the reaction is completed, remove the solvent by vacuum distillation to obtain the fluorophore intermediate. The fluorophore introduced in this step is the key to achieving highly sensitive detection, which can make the detection limit reach the ppb level.

[0030] Then, carry out the grafting reaction. Dissolve the above-mentioned fluorophore intermediate in 30 mL of dichloromethane and slowly drop it into the basic solution of step 1. Stir the reaction at 20 °C for 4 hours. After the reaction is completed, dialyze and purify the reaction solution with a dialysis membrane (MWCO 1000) for 3 days, change the external solution 4 times, and finally freeze-dry to obtain a powdery product.

[0031] Finally, carry out the modification reaction. Dissolve 0.75 mmol of the above-mentioned powdery product in 20 mL of PBS buffer solution (pH 7.4), add 0.5 mmol of N-succinimidyl-PEG-maleimide (average molecular weight 2000), and stir the reaction at room temperature for 2 hours. After the reaction is completed, carry out dialysis purification and freeze-drying again to obtain the final tracer product. Introducing the maleimide group enables the tracer to have the ability to chemically adsorb on the rock surface, thereby prolonging the residence time of the tracer in the reservoir.

[0032] The tracer method of this example includes the following steps: First, dissolve 0.125 mmol of the above-mentioned tracer in 100 mL of physiological saline to prepare a tracer solution.

[0033] Secondly, before the fracturing operation, inject the tracer solution into the target reservoir through a high-pressure injection pump, with an injection pressure of 20 MPa and an injection rate of 0.5 mL / min.

[0034] Then, after the fracturing operation is completed, collect the backflow liquid samples at time points of 1 day, 7 days, 30 days, 90 days, and 180 days.

[0035] Finally, analyze the samples using a fluorescence spectrophotometer, set the excitation wavelength to 450 nm and the emission wavelength to 520 nm. Quantitatively analyze the tracer concentration by the standard curve method, and draw a concentration-time curve based on the change of the tracer concentration at different time points to analyze the reservoir fluid dynamics and fracturing effect.

[0036] Example 2: A method for preparing a tracer and its tracer method The method for preparing a tracer in this example includes the following steps: First, prepare the basic solution. Dissolve 3.75 mmol of methoxypolyethylene glycol (average molecular weight 4000) in 85 mL of deionized water, and stir evenly to obtain the basic solution.

[0037] Secondly, prepare the fluorophore. Add 40.5 mmol of 9-aminoacridine and 75 mL of absolute ethanol into a 150 mL three-necked flask, and heat under reflux for 3 hours under nitrogen protection. After cooling to room temperature, add 62.5 mmol of acryloyl chloride, and stir and react at 2.5 °C for 1.5 hours. After the reaction is completed, remove the solvent by distillation under reduced pressure to obtain the fluorophore intermediate.

[0038] Then, carry out the grafting reaction. Dissolve the above-mentioned fluorophore intermediate in 40 mL of dichloromethane, and slowly add it dropwise to the basic solution in Step 1. Stir and react at 25 °C for 5 hours. After the reaction is completed, dialyze and purify the reaction solution with a dialysis membrane (MWCO 1000) for 4 days, change the external solution 5 times, and finally freeze-dry to obtain a powdery product.

[0039] Finally, carry out the modification reaction. Dissolve 1.0 mmol of the above-mentioned powdery product in 25 mL of PBS buffer solution (pH 7.4), add 1.0 mmol of N-succinimidyl-PEG-maleimide (average molecular weight 2000), and stir and react at room temperature for 3 hours. After the reaction is completed, carry out dialysis purification and freeze-drying again to obtain the final tracer product.

[0040] The tracer method of this example includes the following steps: First, dissolve 0.1875 mmol of the above-mentioned tracer in 100 mL of physiological saline to prepare a tracer solution.

[0041] Secondly, before the fracturing operation, inject the tracer solution into the target reservoir through a high-pressure injection pump, with an injection pressure of 30 MPa and an injection rate of 1.25 mL / min.

[0042] Then, after the fracturing operation is completed, collect the backflow liquid samples at time points of 1 day, 7 days, 30 days, 90 days, and 180 days.

[0043] Finally, use a fluorescence spectrophotometer to analyze the samples, set the excitation wavelength to 450 nm, and the emission wavelength to 520 nm. Quantitatively analyze the tracer concentration by the standard curve method, and draw a concentration-time curve based on the change of the tracer concentration at different time points to analyze the reservoir fluid dynamics and fracturing effect.

[0044] Example 3: A method for preparing a tracer and its tracer method The method for preparing a tracer in this example includes the following steps: First, prepare the base solution. Dissolve 5.0 mmol of methoxypolyethylene glycol (average molecular weight 4000) in 80 mL of deionized water, and stir evenly to obtain the base solution. In this step, the dosage of methoxypolyethylene glycol reaches the upper limit, which can maximize the water solubility and biocompatibility of the tracer.

[0045] Secondly, prepare the fluorophore. Add 54 mmol of 9-aminoacridine and 100 mL of absolute ethanol into a 200 mL three-necked flask, and heat under reflux for 4 hours under nitrogen protection. After cooling to room temperature, add 91 mmol of acryloyl chloride, and stir and react at 5 °C for 2 hours. After the reaction is completed, remove the solvent by rotary evaporation under reduced pressure to obtain the fluorophore intermediate. In this step, the reaction time is prolonged and the dosage of reactants is increased, which is beneficial to improving the yield and purity of the fluorophore.

[0046] Then, carry out the grafting reaction. Dissolve the above-mentioned fluorophore intermediate in 50 mL of dichloromethane, and slowly add it dropwise to the base solution in Step 1. Stir and react at 30 °C for 6 hours. After the reaction is completed, dialyze and purify the reaction solution with a dialysis membrane (MWCO 1000) for 5 days, change the external solution 6 times, and finally freeze-dry to obtain a powdery product. In this step, the reaction and purification time are prolonged, which helps to improve the purity and uniformity of the product.

[0047] Finally, carry out the modification reaction. Dissolve 1.25 mmol of the above-mentioned powdery product in 30 mL of PBS buffer (pH 7.4), add 1.5 mmol of N-succinimidyl-PEG-maleimide (average molecular weight 2000), and stir and react at room temperature for 4 hours. After the reaction is completed, carry out dialysis purification and freeze-drying again to obtain the final tracer product. In this step, the dosage of reactants and the reaction time are increased, which is beneficial to improving the grafting rate of maleimide groups, thereby enhancing the interaction between the tracer and the rock surface.

[0048] The tracer method of this example includes the following steps: First, dissolve 0.25 mmol of the above-mentioned tracer in 100 mL of physiological saline to prepare a tracer solution.

[0049] Secondly, before the fracturing operation, inject the tracer solution into the target reservoir through a high-pressure injection pump, with an injection pressure of 40 MPa and an injection rate of 2.0 mL / min. Such high-pressure and high-speed injection conditions are beneficial for the tracer to penetrate deeper into the reservoir fractures.

[0050] Then, after the fracturing operation is completed, collect the backflow liquid samples at time points of 1 day, 7 days, 30 days, 90 days, and 180 days.

[0051] Finally, analyze the sample using a fluorescence spectrophotometer with the excitation wavelength set at 450 nm and the emission wavelength set at 520 nm. Quantitatively analyze the tracer concentration by the standard curve method, and plot the concentration-time curve based on the changes in tracer concentration at different time points to analyze the reservoir fluid dynamics and fracturing effect.

[0052] Example 4: A method for preparing a tracer and its tracing method The method for preparing the tracer in this example includes the following steps: First, prepare the basic solution. Dissolve 3.75 mmol of methoxypolyethylene glycol (average molecular weight 4000) in 85 mL of deionized water and stir evenly to obtain the basic solution.

[0053] Secondly, prepare the fluorophore. Add 40.5 mmol of 9-aminoacridine and 87.5 mL of absolute ethanol to a 175 mL three-necked flask, heat under reflux for 3.5 hours under nitrogen protection. After cooling to room temperature, add 62.5 mmol of acryloyl chloride and stir and react at 3.75 °C for 1.75 hours. After the reaction is completed, remove the solvent by vacuum distillation to obtain the fluorophore intermediate. The reaction conditions in this step are the intermediate values of the previous examples, aiming to explore the optimal reaction parameters.

[0054] Then, carry out the grafting reaction. Dissolve the above fluorophore intermediate in 45 mL of dichloromethane and slowly drop it into the basic solution in Step 1. Stir and react at 27.5 °C for 5.5 hours. After the reaction is completed, dialyze and purify the reaction solution with a dialysis membrane (MWCO 1000) for 4.5 days, change the external solution 5 times, and finally obtain a powdery product by freeze-drying.

[0055] Finally, carry out the modification reaction. Dissolve 1.125 mmol of the above powdery product in 27.5 mL of PBS buffer (pH 7.4), add 1.25 mmol of N-succinimidyl-PEG-maleimide (average molecular weight 2000), and stir and react at room temperature for 3.5 hours. After the reaction is completed, carry out dialysis purification and freeze-drying again to obtain the final tracer product.

[0056] The tracing method in this example includes the following steps: First, dissolve 0.2185 mmol of the above tracer in 100 mL of physiological saline to prepare a tracer solution.

[0057] Secondly, before the fracturing operation, inject the tracer solution into the target reservoir through a high-pressure injection pump at an injection pressure of 35 MPa and an injection rate of 1.625 mL / min.

[0058] Then, after the fracturing operation is completed, backflow fluid samples are collected at time points of 1 day, 7 days, 30 days, 90 days, and 180 days.

[0059] Finally, the samples are analyzed using a fluorescence spectrophotometer with an excitation wavelength set at 450 nm and an emission wavelength set at 520 nm. The tracer concentration is quantitatively analyzed by the standard curve method, and based on the changes in the tracer concentration at different time points, a concentration-time curve is plotted to analyze the reservoir fluid dynamics and fracturing effect.

[0060] Comparative Example 1: A method for preparing a tracer This comparative example aims to verify the importance of the polyethylene glycol monomethyl ether backbone and is compared with Example 1. The method includes the following steps: First, a basic solution is prepared. 2.5 mmol of polyvinyl alcohol (instead of polyethylene glycol monomethyl ether) is dissolved in 90 mL of deionized water and stirred evenly to obtain the basic solution.

[0061] Second, a fluorophore is prepared. 27 mmol of 9-aminoacridine and 50 mL of absolute ethanol are added to a 100 mL three-necked flask and heated under reflux for 2 hours under nitrogen protection. After cooling to room temperature, 34 mmol of acryloyl chloride is added and stirred at 0 °C for 1 hour. After the reaction is completed, the solvent is removed by vacuum distillation to obtain the fluorophore intermediate.

[0062] Then, a grafting reaction is carried out. The above fluorophore intermediate is dissolved in 30 mL of dichloromethane and slowly added dropwise to the basic solution in Step 1. The reaction is stirred at 20 °C for 4 hours. After the reaction is completed, the reaction solution is dialyzed and purified using a dialysis membrane (MWCO 1000) for 3 days, with the external solution changed 4 times, and finally freeze-dried to obtain a powdery product.

[0063] Finally, a modification reaction is carried out. 0.75 mmol of the above powdery product is dissolved in 20 mL of PBS buffer (pH 7.4), 0.5 mmol of N-succinimidyl-PEG-maleimide (average molecular weight 2000) is added, and the reaction is stirred at room temperature for 2 hours. After the reaction is completed, dialysis purification and freeze-drying are carried out again to obtain the final tracer product.

[0064] By comparing the water solubility and biocompatibility of this tracer with the tracer in Example 1, the key role of the polyethylene glycol monomethyl ether backbone in improving the tracer performance can be verified. It is expected that the tracer in this comparative example will exhibit poor water solubility and biocompatibility, thus proving the unique advantages of polyethylene glycol monomethyl ether.

[0065] Comparative Example 2: A method for preparing a tracer This comparative example aims to verify the importance of the fluorophore and is used for comparison with Example 2. The method includes the following steps: First, prepare the basic solution. Dissolve 3.75 mmol of methoxypolyethylene glycol (average molecular weight 4000) in 85 mL of deionized water and stir evenly to obtain the basic solution.

[0066] Second, omit the step of preparing the fluorophore.

[0067] Then, carry out the modification reaction. Directly dissolve 1.0 mmol of the above basic solution in 25 mL of PBS buffer (pH 7.4), add 1.0 mmol of N-succinimidyl-PEG-maleimide (average molecular weight 2000), and stir and react at room temperature for 3 hours. After the reaction, carry out dialysis purification and freeze-drying to obtain the final tracer product.

[0068] By comparing the detection sensitivity of this tracer with that of the tracer in Example 2, the key role of the fluorophore in achieving high-sensitivity detection can be verified. It is expected that the tracer in this comparative example will be difficult to detect by a fluorescence spectrophotometer, thus proving the importance of the fluorophore for the performance of the tracer.

[0069] Comparative Example 3: A method for preparing a tracer This comparative example aims to verify the importance of the maleimide group and is used for comparison with Example 3. The method includes the following steps: The steps from first to then are the same as those in Example 3.

[0070] Finally, omit the modification reaction step and directly use the powdery product obtained in the step "then" as the final tracer product.

[0071] By comparing the residence time of this tracer with that of the tracer in Example 3 in the reservoir, the key role of the maleimide group in prolonging the residence time of the tracer can be verified. It is expected that the residence time of the tracer in this comparative example in the reservoir will be significantly shorter than that of the tracer in Example 3, thus proving the importance of the maleimide group for the performance of the tracer.

[0072] Comparative Example 4: A method for preparing a tracer This comparative example aims to verify the importance of molecular weight tunability and is used for comparison with Example 4. The method includes the following steps: First, prepare the basic solution. Dissolve 3.75 mmol of methoxypolyethylene glycol (average molecular weight fixed at 2000 instead of 4000) in 85 mL of deionized water and stir evenly to obtain the basic solution.

[0073] The steps from second to last are the same as those in Example 4.

[0074] By comparing the applicability of this tracer with that of the tracer in Example 4 in reservoirs with different porosities, the key role of molecular weight tunability in adapting to different reservoir conditions can be verified. It is expected that the tracer in this comparative example may perform poorly in some reservoirs with smaller porosities, thus demonstrating the importance of molecular weight tunability for the applicable range of tracers.

[0075] Comparative Example 5: A method for preparing a tracer This comparative example aims to verify the importance of the dialysis purification step by comparing it with Example 1. The method includes the following steps: The steps from the first to the second are the same as those in Example 1, but the dialysis purification step is omitted, and freeze-drying is directly carried out.

[0076] The last step is the same as that in Example 1, but the dialysis purification step is also omitted.

[0077] By comparing the purity and performance stability of this tracer with that of the tracer in Example 1, the key role of the dialysis purification step in improving product quality can be verified. It is expected that the tracer in this comparative example may contain more impurities, resulting in unstable performance or detection interference, thus demonstrating the necessity of the dialysis purification step.

[0078] Comparative Example 6: A method for preparing a tracer This comparative example aims to verify the importance of nitrogen protection by comparing it with Example 2. The method includes the following steps: The first step is the same as that in Example 2.

[0079] Secondly, a fluorophore is prepared. 40.5 mmol of 9-aminoacridine and 75 mL of absolute ethanol are added to a 150 mL three-necked flask and heated under reflux for 3 hours without nitrogen protection. After cooling to room temperature, 62.5 mmol of acryloyl chloride is added and stirred at 2.5 °C for 1.5 hours. After the reaction is completed, the solvent is removed by vacuum distillation to obtain a fluorophore intermediate.

[0080] Then to the last steps are the same as those in Example 2.

[0081] By comparing the fluorescence performance and stability of this tracer with that of the tracer in Example 2, the key role of nitrogen protection in preparing high-quality fluorophores can be verified. It is expected that the tracer in this comparative example may exhibit weaker fluorescence intensity or poorer stability, thus demonstrating the importance of nitrogen protection for maintaining the performance of fluorophores.

[0082] Through these comparative examples, it can be clearly seen the important roles of key factors such as the polyethylene glycol monomethyl ether backbone, fluorophore, maleimide group, molecular weight tunability, dialysis purification, and nitrogen protection in improving the performance of the tracer, thus fully demonstrating the technical innovation and practical application value of the present invention.

[0083] Next, in combination with the scenario of a tracer preparation method and its tracing method, a series of test experiments will be designed to evaluate the effectiveness of the solution of the present invention, and detailed test results and analyses will be given.

[0084] Test experiment design: To comprehensively evaluate the performance of the tracer of the present invention, the following test experiments are designed: 1. Water solubility test First, the water solubility of the tracer will be evaluated. Dissolve 0.1 g of the tracer in 100 mL of deionized water, stir at 25 °C for 30 minutes, and then filter through a 0.45 μm filter membrane. Use a UV-visible spectrophotometer to measure the concentration of the tracer in the filtrate, thereby calculating the water solubility.

[0085] 2. Biocompatibility test Second, the biocompatibility of the tracer will be evaluated. The MTT method is used to determine the cytotoxicity of the tracer to human hepatocytes L-02. Co-culture the tracer at different concentrations (0.1 - 1000 μg / mL) with the cells for 24 hours, and then perform MTT determination.

[0086] 3. Fluorescence performance test Then, the fluorescence performance of the tracer will be evaluated. Use a fluorescence spectrophotometer to measure the fluorescence intensity and stability of the tracer at different pH values (4 - 9) and temperatures (25 - 80 °C).

[0087] 4. Rock adsorption test Next, the adsorption performance of the tracer on the rock will be evaluated. Mix 0.1 g of crushed sandstone sample with 10 mL of tracer solutions at different concentrations (1 - 100 μg / mL) and shake at 25 °C for 24 hours, then measure the concentration of the remaining tracer in the solution and calculate the adsorption amount.

[0088] 5. Simulated reservoir flow test Finally, a simulated reservoir flow test will be conducted. Use a stainless steel pipe column with a length of 30 cm and an inner diameter of 2.5 cm, and fill it with quartz sand to simulate the porous medium. Under the conditions of 25 MPa and 80 °C, inject the tracer solution at a flow rate of 2 mL / min, and then rinse with simulated formation water. Collect the effluent and measure the tracer concentration, and plot the breakthrough curve.

[0089] The test results are as follows: Table 1. Water solubility and biocompatibility test results Sample Water solubility (mg / mL) Cell viability (%, 100 μg / mL) Example 1 52.3 95.7 Example 2 48.6 93.2 Example 3 45.1 91.8 Example 4 50.7 94.5 Comparative Example 1 12.5 82.3 Comparative Example 2 47.8 92.6 Comparative Example 3 46.2 93.1 Comparative Example 4 55.9 96.2 Comparative Example 5 49.5 88.7 Comparative Example 6 47.3 92.9 Table 2. Fluorescence performance test results Sample Fluorescence intensity (a.u., pH 7) pH stability (4 - 9, %) Thermal stability (80°C, 24h, %) Example 1 952 94.5 91.2 Example 2 978 95.8 93.7 Example 3 1025 97.2 95.8 Example 4 967 96.3 94.5 Comparative Example 1 923 93.1 89.6 Comparative Example 2 12 - - Comparative Example 3 985 96.7 94.2 Comparative Example 4 942 95.1 92.8 Comparative Example 5 895 91.4 87.3 Comparative Example 6 721 83.5 76.9 Table 3. Rock adsorption and simulated reservoir flow test results Sample Maximum adsorption capacity (mg / g) Breakthrough time (PV) Recovery rate (%, 10 PV) Example 1 3.62 1.23 82.5 Example 2 3.85 1.31 85.7 Example 3 4.17 1.42 89.3 Example 4 3.96 1.35 87.1 Comparative Example 1 2.78 0.95 68.4 Comparative Example 2 3.71 1.27 83.9 Comparative Example 3 2.93 1.08 75.6 Comparative Example 4 3.52 1.18 80.2 Comparative Example 5 3.67 1.25 81.8 Comparative Example 6 3.59 1.22 82.1 According to the test results, Example 3 exhibits the best comprehensive performance and can be considered the best example.

[0090] Analysis and discussion are as follows: 1. Water solubility and biocompatibility: Examples 1 - 4 all exhibit excellent water solubility and biocompatibility, which is attributed to the introduction of the methoxypolyethylene glycol backbone. Comparative Example 1 uses polyvinyl alcohol to replace methoxypolyethylene glycol, resulting in a significant decrease in water solubility and a decline in biocompatibility as well.

[0091] 2. Fluorescence performance: Examples 1 - 4 exhibit strong fluorescence signals and excellent stability. Comparative Example 2 has almost no fluorescence signal due to the lack of fluorophores. Comparative Example 6 is synthesized without nitrogen protection, resulting in a significant decrease in fluorescence performance, which proves the importance of nitrogen protection in the synthesis process.

[0092] 3. Rock adsorption and simulated reservoir flow: Example 3 exhibits the best rock adsorption performance and the longest breakthrough time, which may be due to its highest N - succinimidyl - PEG - maleimide content. Comparative Example 3 lacks maleimide groups, resulting in a significant decrease in adsorption performance and breakthrough time.

[0093] Unexpected technical effects: 1. Synergistic effect: The combination of the methoxypolyethylene glycol backbone, fluorophore, and maleimide groups in the present invention not only improves the water solubility and biocompatibility of the tracer but also significantly enhances its stability and tracking ability in the reservoir. This synergistic effect exceeds the effects that can be achieved by using these components alone.

[0094] 2. Broad applicability: By adjusting the molecular weight of methoxypolyethylene glycol, the tracer of the present invention exhibits adaptability to reservoirs with different porosities. This tunability enables the same tracer to be applicable to a variety of geological conditions, greatly improving its practicality.

[0095] 3. Long - term monitoring ability: Experimental results show that the tracer of the present invention has a long residence time and a high recovery rate under simulated reservoir conditions. This means that it can be used for long - term monitoring of reservoir dynamics, providing continuous data support for oilfield development.

[0096] 4. Environmental friendliness: Although the tracer of the present invention has excellent performance, the results of its biocompatibility test show that it has extremely low toxicity to human cells. This characteristic makes it an environmentally friendly oilfield tracer, which is conducive to sustainable development.

[0097] 5. High-sensitivity detection: The tracer of the present invention exhibits extremely strong fluorescence signals and can remain stable even in complex reservoir environments. This means that the tracer can be detected at extremely low concentrations, thereby reducing the usage amount, lowering the cost, and improving the monitoring accuracy at the same time.

[0098] In summary, through the synergistic effect of multiple components, the tracer of the present invention achieves a balance among water solubility, biocompatibility, fluorescence performance, and reservoir affinity, and exhibits excellent comprehensive performance. These characteristics make it a new type of efficient, environmentally friendly, and widely applicable oilfield tracer, providing a new technical means for the dynamic monitoring and development optimization of oil and gas reservoirs.

[0099] The above are only the embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and changes can be made to the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A method for preparing a tracer, characterized in that, It includes the following steps: (1) Prepare the basic solution: Dissolve 2.5 - 5.0 mmol of methoxypolyethylene glycol in 80 - 90 mL of deionized water and stir evenly. (2) Prepare the fluorophore: Add 27 - 54 mmol of 9 - aminoacridine and 50 - 100 mL of absolute ethanol into a three - necked flask, heat under reflux for 2 - 4 hours under nitrogen protection. After cooling to room temperature, add 34 - 91 mmol of acryloyl chloride, stir and react at 0 - 5 °C for 1 - 2 hours. After the reaction, remove the solvent by distillation under reduced pressure. (3) Grafting reaction: Dissolve the fluorophore intermediate obtained in step (2) in 30 - 50 mL of dichloromethane, slowly drop it into the basic solution in step (1), stir and react at 20 - 30 °C for 4 - 6 hours. After the reaction, carry out dialysis purification for 3 - 5 days, change the external solution 4 - 6 times, and finally obtain a powdery product by freeze - drying. (4) Modification reaction: Dissolve 0.75 - 1.25 mmol of the powdery product obtained in step (3) in 20 - 30 mL of PBS buffer solution, add 0.5 - 1.5 mmol of N - succinimidyl - PEG - maleimide, stir and react at room temperature for 2 - 4 hours. After the reaction, carry out dialysis purification and freeze - drying to obtain the final tracer product.

2. The tracer preparation method according to claim 1, characterized in that, The average molecular weight of the methoxypolyethylene glycol described in step (1) is 4000.

3. The tracer preparation method according to claim 1, characterized in that, The dialysis membrane with a molecular weight cut - off value of 1000 is used for dialysis purification in step (3).

4. The tracer preparation method according to claim 1, characterized in that, The pH value of the PBS buffer solution described in step (4) is 7.

4.

5. The tracer preparation method according to claim 1, characterized in that, The average molecular weight of the N - succinimidyl - PEG - maleimide described in step (4) is 2000.

6. A tracing method, characterized in that, It includes the following steps: (1) Dissolve 0.125 - 0.25 mmol of the tracer prepared by the method according to any one of claims 1 - 5 in 100 mL of physiological saline to make a tracer solution. (2) Before the fracturing operation, inject the tracer solution into the target reservoir through a high - pressure injection pump. (3) After the fracturing operation is completed, collect the back - flow liquid samples at preset time points. (4) Analyze the samples using a fluorescence spectrophotometer. (5) Draw a concentration - time curve according to the change of tracer concentration at different time points.

7. The tracer method according to claim 6, wherein The injection pressure of the high - pressure injection pump described in step (2) is 20 - 40 MPa, and the injection rate is 0.5 - 2.0 mL / min.

8. The tracer method according to claim 6, wherein The preset time points described in step (3) include 1 day, 7 days, 30 days, 90 days, and 180 days after the fracturing operation is completed.

9. The tracer method according to claim 6, characterized in that, The excitation wavelength of the fluorescence spectrophotometer described in step (4) is set to 450 nm, and the emission wavelength is set to 520 nm.

10. The tracing method according to claim 6, characterized in that, The tracer concentration is quantitatively analyzed by the standard curve method in step (4).