Preparation method and application of nitrogen-doped coal-based carbon dot oil field tracer agent

Abstract

The invention provides a preparation method and application of a nitrogen-doped coal-based carbon dot oil field tracer agent. The tracer is prepared from weathered coal as a raw material through a hydrothermal synthesis method and has the characteristics of good fluorescence stability and high quantum yield, and the preparation process is simple, green and environment-friendly. The method is low in cost, high in yield, easy for industrial production and wide in market application prospect. In oil field tracing, the tracer agent is good in water solubility, high in stability, easy and convenient to analyze, high in sensitivity, free of radioactivity, small in toxicity, environmentally friendly, free of influence on the degree of mineralization, good in compatibility with additives such as fracturing fluid and the like and free of influence on oil displacement operation. The problems that a chemical tracer is high in cost and large in detection error, a radioactive isotope tracer is complex in operation and high in risk, and a non-radioactive isotope tracer is limited in variety and high in cost are solved. The tracer enriches the types of oil field tracers, widens the application field of carbon dots, has positive influence on improvement of the oil field exploitation rate, and has important significance on solving the problem of oil and gas resource shortage.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield mining engineering, and in particular relates to a preparation method of a nitrogen-doped coal-based carbon dot oilfield tracer and an application thereof. Background Art

[0002] With the increasing difficulty of oil field development in my country, the slow growth of production and the reduction of traditional oil reservoirs, the importance of unconventional resources such as tight oil and gas has become increasingly prominent. However, due to its low permeability and porosity, traditional extraction methods are difficult to achieve ideal results. Therefore, the combination of horizontal wells and hydraulic volume fracturing has become a common practice to improve extraction efficiency. In order to effectively evaluate the extraction effect and predict production dynamics, it is crucial to accurately describe the fracture network formed after fracturing, which provides an effective way to overcome the current difficulties in oil resource development.

[0003] Oilfield tracer technology is a technical means to track and monitor the migration, distribution and geological fluid dynamics of oil by introducing specific compounds or markers into the oil system. This technology helps petroleum engineers and geologists better understand and master the material flow laws of petroleum geological reservoirs, thereby improving the efficiency and benefits of oilfield development. Oilfield tracers can track the migration path and rate of oil in geological reservoirs, study the effective thickness, permeability and other characteristics of oil reservoirs, and provide a scientific basis for oilfield development and exploration. In addition, by introducing specific tracers into the oil water drive or gas drive system injected downhole, the oil flow process can be monitored in real time, including the migration speed, movement path, distribution, etc. of oil, providing a reference for reservoir management and optimized development. Oil well leakage is one of the common problems in oilfield development. The introduction of tracers can realize online monitoring and judgment of oil well leakage, timely detect problems and take corresponding measures to reduce the impact of oil well leakage on the environment and economy. Long-distance transportation of oil pipelines is an indispensable part of the oil development process. The application of tracers can realize real-time monitoring of oil transportation flow, quality and leakage, and improve the safety and reliability of oil pipeline transportation.

[0004] Coal-based carbon dots (CBCDs) are a new type of carbon material. Due to their unique optical and chemical properties, they show broad application potential in biomedicine, energy storage, environmental governance and other fields. As a tracer, CBCDs have high chemical stability. Compared with traditional fluorescent tracers, CBCDs show better stability in extreme environments and can withstand high temperature, high pressure, acid and alkali conditions, which gives them significant tracing advantages in complex oilfield environments. Summary of the invention

[0005] The purpose of the present invention is to provide a preparation method and use of a nitrogen-doped weathered coal carbon dot oilfield tracer, to synthesize a nitrogen-doped coal-based carbon dot tracer without consuming a large amount of acid, thereby solving the problems of existing oilfield tracers such as high toxicity, poor stability and poor environmental performance.

[0006] The implementation process of the present invention is as follows: A method for preparing a nitrogen-doped weathered coal carbon dot oilfield tracer, characterized in that it includes the following steps: placing weathered coal and one or more dopants in a hydrothermal reactor according to a certain molar ratio, adding an appropriate volume of solvent, ultrasonicating, and heating the reaction under temperature and time control, cooling to room temperature after the reaction is completed, removing insoluble impurities through a membrane filter, and finally using a rotary evaporator to remove water and volatile impurities to obtain a nitrogen-doped weathered coal carbon dot oilfield tracer.

[0007] Furthermore, 200-mesh weathered coal was used to ensure the uniformity of the reaction.

[0008] The nitrogen dopant is any one or a mixture of urea, tris(hydroxymethyl)aminomethane, L-glutamic acid, ammonium acetate, and ethylenediaminetetraacetic acid to achieve effective nitrogen doping.

[0009] The mass ratio of weathered coal and dopants is 1:10~10:1 to ensure the doping effect.

[0010] The total weight of weathered coal and dopants is 100 mg~1 kg to meet the preparation needs of different scales.

[0011] The solvent is selected from any one or a mixture of dilute nitric acid, ammonia water, and distilled water to provide a suitable reaction environment.

[0012] The volume of the solvent is 2mL~30mL to meet the needs of different reaction scales.

[0013] The ultrasonic treatment time is 0.5 to 2 hours to ensure sufficient mixing and dissolution of the raw materials.

[0014] The reaction temperature is 150-250° C. and the reaction time is 4-12 hours to achieve an efficient synthesis reaction.

[0015] Positive effects of the present invention: The method of the present invention uses weathered coal as the main raw material, and the raw material cost is low. It provides a new way to achieve high-value utilization of coal resources, and the prepared carbon quantum dots have high added value. It is prepared using a simple hydrothermal method without consuming a large amount of acid. The synthesized nitrogen-doped carbon dot tracer is green, environmentally friendly, low in toxicity, pollution-free, and has high fluorescence intensity and good stability. The present invention not only enriches the types of oil field tracers, but also can play a key role in the process of oil field exploration and exploitation, helping to increase the output of oil wells and extend the life of oil fields, which is of great significance to solving the current shortage of oil and gas resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a graph showing the concentration retention rate of the carbon dot tracer prepared in Example 5 in a high temperature environment.

[0017] Figure 2 Graph showing the concentration retention rate of the carbon dot tracer prepared by using Examples 1, 2, 4 and 6 in different environments.

[0018] Figure 3 This is a graph showing the concentration retention rate of the carbon dot tracer prepared in Example 3 in different pH environments.

[0019] Figure 4 This is a graph showing the concentration retention rate of the carbon dot tracer prepared in Example 5 in a high temperature environment. DETAILED DESCRIPTION

[0020] Some embodiments of the process of the present invention are as follows:

[0021] Example 1 Weigh 200 mesh weathered coal powder and urea in a mass ratio of 1:1 in a polytetrafluoroethylene reactor liner, add 20 mL of distilled water, and fully disperse them by ultrasound. Put the reactor liner into the shell of the high-pressure reactor and tighten it, place it in an oven at 180°C and heat it for 8 hours. After the reactor cools to room temperature, take out the solution in the reactor liner, centrifuge it at 5000 rpm for 15 minutes, filter it with a microporous membrane with a pore size of 0.22 μm, and then remove the solvent by a rotary evaporator. The solid product obtained by rotary evaporation is dispersed in ultrapure water to obtain the nitrogen-doped weathered coal carbon point tracer solution. The best excitation wavelength is 353 nm and the best emission wavelength is 457 nm as tested by a fluorescence spectrometer.

[0022] Example 2 Weigh 200-mesh weathered coal powder and urea in a mass ratio of 1:5 in a polytetrafluoroethylene reactor liner, add 20 mL of distilled water, and fully disperse them by ultrasound. Put the reactor liner into the shell of the high-pressure reactor and tighten it, place it in a 200°C oven and heat it for 6 hours. After the reactor cools to room temperature, take out the solution in the reactor liner, centrifuge it at 5000rpm for 15 minutes, filter it with a microporous membrane with a pore size of 0.22μm, and then remove the solvent by a rotary evaporator. The solid product obtained by rotary evaporation is dispersed in ultrapure water to obtain a purified blue light carbon dot tracer solution. The best excitation wavelength is 360nm and the best emission wavelength is 459nm as tested by a fluorescence spectrometer.

[0023] Example 3 Weigh 200 mesh weathered coal powder and tris(hydroxymethyl)aminomethane) in a mass ratio of 1:1 in a polytetrafluoroethylene reactor liner, add 20 mL of distilled water and 0.2 mL of ammonia water, and disperse them fully by ultrasound. Put the reactor liner into the shell of the high-pressure reactor and tighten it, place it in a 210°C oven and heat it for 6 hours. After the reactor cools to room temperature, take out the solution in the reactor liner, centrifuge it at 10 rpm for 15 minutes, filter it with a microporous membrane with a pore size of 0.22 μm, and then remove the solvent by a rotary evaporator. The solid product obtained by rotary evaporation is dispersed in ultrapure water to obtain a purified tracer solution. The best excitation wavelength is 362 nm and the best emission wavelength is 462 nm as tested by a fluorescence spectrometer.

[0024] Example 4 Weigh 200-mesh weathered coal powder and tris(hydroxymethyl)aminomethane) in a mass ratio of 1:5 in a polytetrafluoroethylene reactor liner, add 20 mL of 0.01 mol / L dilute nitric acid, and disperse them fully by ultrasound. Put the reactor liner into the shell of the high-pressure reactor and tighten it, place it in a 190°C oven and heat it for 7 hours. After the reactor cools to room temperature, take out the solution in the reactor liner, centrifuge it at 5000 rpm for 15 minutes, filter it with a microporous membrane with a pore size of 0.22 μm, and then remove the solvent by a rotary evaporator. The solid product obtained by rotary evaporation is dispersed in ultrapure water to obtain a purified cyan carbon dot tracer solution. The fluorescence spectrometer test shows that the optimal excitation wavelength is 364 nm and the optimal emission wavelength is 460 nm.

[0025] Example 5 Weigh 200 mesh weathered coal powder and L-glutamic acid in a mass ratio of 3:5 in a polytetrafluoroethylene reactor liner, add 20 mL of distilled water, and fully disperse them by ultrasound. Put the reactor liner into the shell of the high-pressure reactor and tighten it, place it in a 210°C oven and heat it for 6 hours. After the reactor cools to room temperature, take out the solution in the reactor liner, centrifuge it at 5000rpm for 15 minutes, filter it with a microporous membrane with a pore size of 0.22μm, and then remove the solvent by a rotary evaporator. The solid product obtained by rotary evaporation is dispersed in ultrapure water to obtain a purified tracer solution. The best excitation wavelength is 340nm and the best emission wavelength is 456nm as tested by a fluorescence spectrometer.

[0026] Example 6 Weigh 200-mesh weathered coal powder and ammonium acetate in a mass ratio of 1:1.5 in a polytetrafluoroethylene reactor liner, add 20 mL of 1 mol / L ammonia water, and disperse them fully by ultrasound. Put the reactor liner into the shell of the high-pressure reactor and tighten it, place it in a 210°C oven for 6 hours, and after the reactor is cooled to room temperature, take out the solution in the reactor liner, centrifuge it at 5000 rpm for 15 minutes, filter it with a microporous membrane with a pore size of 0.22 μm, and then remove the solvent by a rotary evaporator. The solid product obtained by rotary evaporation is dispersed in ultrapure water to obtain a carbon dot tracer solution. The best excitation wavelength is 364 nm and the best emission wavelength is 450 nm as tested by a fluorescence spectrometer.

[0027] Example 7 Weigh 200-mesh weathered coal powder and ethylenediaminetetraacetic acid in a mass ratio of 1:1 in a polytetrafluoroethylene reactor liner, add 20 mL of distilled water, and fully disperse them by ultrasound. Put the reactor liner into the shell of the high-pressure reactor and tighten it, place it in a 200°C oven and heat it for 8 hours. After the reactor cools to room temperature, take out the solution in the reactor liner, centrifuge it at 5000rpm for 15 minutes, filter it with a microporous membrane with a pore size of 0.22μm, and then remove the solvent by a rotary evaporator. The solid product obtained by rotary evaporation is dispersed in ultrapure water to obtain a carbon dot tracer solution. The best excitation wavelength is 360nm and the best emission wavelength is 465nm as tested by a fluorescence spectrometer.

[0028] Application Example 1 The present invention investigates the influence of different combinations and concentrations of mineralization solutions on the fluorescence properties of carbon dot oilfield tracers. Mineralization solutions with mass fractions of 10% sodium chloride and 1.5% calcium chloride were prepared and used to fix the volume of carbon dot oilfield tracers. On this basis, a carbon dot tracer solution with a concentration of 100 mg / L in a mineralized environment was obtained. The stability of the carbon dot tracer in a certain mineralization environment was evaluated by detecting the intensity at the maximum emission wavelength at the optimal excitation wavelength of the carbon dot tracer and calculating the tracer concentration retention rate. The experimental results show that in a high-mineralization water environment, the prepared carbon dot tracer has good stability in a high-mineralization environment.

[0029] Application Example 2 In order to investigate the distribution of carbon dot tracers in a mixed solution of water and crude oil and its effect on the fluorescence properties of carbon dot tracers, a mixed solution of crude oil and 100 mg / L carbon dot tracer aqueous solution with a volume ratio of 80 mL / 20 mL, 50 mL / 50 mL, and 20 mL / 80 mL was prepared three times. The intensity at the maximum emission wavelength was detected at the optimal excitation wavelength of the carbon dot tracer, and the tracer concentration retention rate was calculated to evaluate the distribution of the carbon dot tracer in a mixed solution environment of water and crude oil. The results are shown in Figure 2. Figure 2 As shown. Figure 2It can be seen that in the mixed environment of crude oil and water, the concentration retention rate of the carbon dot tracer does not change much, which shows that the carbon dot tracer prepared by the present invention has good water solubility.

[0030] Application Example 3 The pH value of formation water varies from oil fields, different blocks and even different well groups. The pH value of produced water from most oil fields is in the range of 6-8. In addition, due to the widespread application of oil enhancement technologies in recent years, such as acid fracturing, the pH value of the formation is complex and changeable. Therefore, in order to better evaluate whether carbon dot tracers can be used for oil field tracing, the present invention investigates the effect of pH on the fluorescence properties of carbon dot tracers. Solutions with a pH value in the range of 2 to 13 were prepared three times to fix the volume of each carbon dot oil field tracer. The intensity at the maximum emission wavelength was detected at the optimal excitation wavelength of the carbon dot tracer, the tracer concentration retention rate was calculated, and the stability of the carbon dot tracer in an acidic and alkaline environment was evaluated. The results are as follows. Figure 3 As shown. Figure 3 It can be seen that under the environments of pH 5, 6, 7, 8, and 9, the concentration retention rate of the carbon dot tracer does not change much, which shows that the prepared carbon dot tracer has good stability in most oil field acid-base environments.

[0031] Application Example 4 During the fracturing process of tight oil fields, tracers need to be injected into the formation together with the fracturing fluid, and the tracer concentration must be detected in the fracturing flowback fluid. Therefore, the present invention investigates the effect of fracturing fluid on the fluorescence properties of carbon dot tracers. The guar gum fracturing fluid is used to make a fixed volume of carbon dot oilfield tracer to obtain a carbon dot tracer solution with a concentration of 100 mg / L under the fracturing system environment, which is prepared three times. Taking the cyan carbon dot tracer as an example, the intensity at the maximum emission wavelength is detected at the optimal excitation wavelength of the carbon dot tracer, the tracer concentration retention rate is calculated, and the stability of the carbon dot tracer in the fracturing system is evaluated. The results are as follows: Figure 2 As shown. Figure 2 It can be seen that in the guar gum fracturing fluid environment, the fluorescence intensity of the carbon dot tracer is still very stable, which shows that the prepared carbon dot tracer has good compatibility in the fracturing fluid environment.

[0032] Application Example 5 The reservoir temperature of most oil fields is in the range of 50-90°C, so the oil field tracer needs to be temperature resistant. Therefore, the present invention investigates the effect of temperature on the concentration retention rate of the carbon dot tracer. A 100 mg / L carbon dot tracer solution was placed in a 50°C and 90°C thermostat and configured three times. The test lasted 30 days, with detection every 5 days. The intensity at the maximum emission wavelength was detected at the optimal excitation wavelength of the carbon dot tracer, the tracer concentration retention rate was calculated, and the stability of the carbon dot tracer at the reservoir temperature was evaluated. The results are as follows: Figure 3 As shown. Figure 3It can be seen that under high temperature environment, the concentration of carbon dot tracer does not change much with time, which shows that the prepared carbon dot fluorescent tracer has good temperature resistance.

[0033] Application Example 6 The basis for the tracer monitoring technology to analyze the reservoir properties is that the amount of tracer adsorbed in the formation is extremely low or zero. In fact, affected by the reservoir properties and tracer structure, there is a certain amount of adsorption of the tracer during the migration of the formation. If the selected tracer has a high adsorption, it will lead to problems such as reduced tracer recovery and delayed production. Therefore, the present invention investigates the effects of natural core powder and ceramic fracturing support agents on the concentration retention rate of carbon dot tracers. Measure an appropriate amount of 100 mg / L carbon dot tracer solution and place it in a test tube containing 5 g of natural core powder and 5 g of ceramic fracturing support agent, and configure it three times. Detect the intensity at the maximum emission wavelength at the optimal excitation wavelength of the carbon dot tracer, calculate the tracer concentration retention rate, and evaluate the adsorption of the carbon dot tracer under the reservoir rock sand. The results are as follows: Figure 2 As shown. Figure 2 It can be seen that in the static simulated formation adsorption environment, the fluorescence intensity of the carbon dot tracer is still very stable. The present invention shows that the prepared carbon dot fluorescent tracer has a lower adsorption amount in the reservoir environment.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a nitrogen-doped coal-based carbon dot oilfield tracer, characterized in that: The method comprises the following steps: placing weathered coal and nitrogen-containing dopants in a hydrothermal reactor according to a certain mass ratio, adding an appropriate volume of solvent, heating and reacting at a controlled temperature and time, cooling to room temperature after the reaction is completed, removing insoluble impurities through a membrane filter, and finally removing the solvent using a rotary evaporator to obtain a nitrogen-doped coal-based carbon dot oilfield tracer.

2. The method according to claim 1, wherein the nitrogen dopant is any one of urea, tris(hydroxymethyl)aminomethane, L-glutamic acid, ammonium acetate, and ethylenediaminetetraacetic acid, or a mixture of any of them.

3. The method according to claim 1, characterized in that :The mass ratio of the carbon source to the dopant is 1:10~10:

1.

4. The method according to claim 1, characterized in that :The weight of the carbon source and the dopant is 100 mg ~ 1 kg.

5. The method according to claim 1, characterized in that The solvent is selected from any one of nitric acid, ammonia water, distilled water or a mixture of any of the above.

6. The method according to claim 1, characterized in that The solvent is selected from any one of nitric acid, ammonia water, distilled water or a mixture of any of the above.

7. The method according to claim 1, characterized in that : The reaction temperature is 150~250°C and the reaction time is 4~12h.

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