Preparation method of carbon quantum dot tracing oil displacement mixture

Abstract

The invention relates to a preparation method of a carbon quantum dot tracing oil displacement mixture, the carbon quantum dot tracing oil displacement mixture is prepared by using a self-made carbon quantum dot tracer, a hydrophobic surfactant and a skeleton monomer as synthetic raw materials through a hydrothermal method, the agent contains hydrophobic groups, interfacial tension between water and oil can be reduced, and the oil displacement efficiency is improved. Dispersion and migration of oil drops in water are promoted, so that fluid flow becomes easy; meanwhile, the agent further comprises carbon quantum dots which can indicate the flowing path of formation fluid and evaluate the oil displacement effect of the synthetic agent and the microfracture distribution condition of a target formation, relates to the technical field of quantum dot tracing and oil displacement, and provides a new thought, method and technology for improving the recovery efficiency by adopting the agent on an oil field site.

Description

Technical Field

[0001] The invention relates to the technical field of quantum dot tracing and oil displacement, and in particular to the preparation of a carbon quantum dot tracing and oil displacement mixture. Background Art

[0002] In recent years, carbon quantum dots and their derivative materials have been favored by the majority of oilfield researchers due to their advantages such as high fluorescence quantum yield, easy detection, versatility, low cost, environmental friendliness, stable optical and chemical properties, and have achieved certain achievements in the research process of this technology. As a new type of oil recovery technology, carbon quantum dot tracer flooding mixture has gradually attracted attention in improving oil recovery. Combining carbon quantum dots with surfactants or polymers can obtain relevant data for oil recovery effect evaluation while improving oil recovery, providing support for the improvement of subsequent oil recovery technology. However, the research and application of carbon quantum dots as tracers in oil fields are more focused on evaluating well connectivity, production profiles and hydraulic fracturing effects, and there are very few studies on combining carbon quantum dots with surfactants or polymers as tracer flooding agents. The research on carbon quantum dot tracer flooding mixture is in the initial exploration stage. The research focus of the majority of researchers is mainly on the synthesis of functionalized carbon quantum dots, the combination of carbon quantum dots with other flooding mixtures, and oilfield application tests. Based on the above technical background, this study has prepared an agent with both tracing and oil displacement effects. Since the agent contains hydrophobic groups, it can reduce the interfacial tension between water and oil, promote the dispersion and migration of oil droplets in water, and make the fluid flow easier; at the same time, the agent also includes carbon quantum dots, which can indicate the flow path of formation fluids and evaluate the oil displacement effect of the synthetic agent and the distribution of microcracks in the target formation. Summary of the invention

[0003] Based on the limitations of the prior art, the present invention provides a method for preparing a carbon quantum dot tracer oil-displacing mixture. The preparation method uses a homemade carbon quantum dot tracer, a hydrophobic surfactant, and a skeleton monomer as synthetic raw materials, and utilizes a hydrothermal method to carry out a copolymerization reaction. The method is simple and convenient to operate, and the reaction conditions are easy to control. The synthesized carbon quantum dot tracer oil-displacing mixture can reduce the interfacial tension between oil and water in the formation fluid, has a strong oil displacement capacity, and has an obvious effect. At the same time, it can achieve one-step production and evaluation, and is convenient to analyze and has a low cost compared to traditional oil displacement evaluation technologies.

[0004] The technical solution provided by the present invention includes the following contents:

[0005] (1) Preparation of carbon quantum dot tracers

[0006] After the solute and the solvent are mixed evenly, they are transferred to a high-temperature and high-pressure reactor with a polytetrafluoroethylene liner, and nitrogen is passed for half an hour to remove the air in the reaction system, and then the reaction time and reaction temperature are set for reaction. After the reaction is completed, a large amount of impurities are removed by centrifugation and further purified by dialysis, and finally dried by a freeze dryer to obtain the target product. The solvent is one or more of pure water, ethylene glycol, formamide, N,N-dimethylformamide, N,N-diethylformamide, and dimethylaminoformyl chloride; the carbon source is one or more of citric acid, sodium citrate, trisodium citrate, p-phenylenediamine, o-phenylenediamine, 1,3-dihydroxynaphthalene, urea, and 1,2-diaminoethane; the mass ratio of the solute to the solvent is 10% to 20%; the reaction time is 2 to 12 hours, the reaction temperature is 160 to 220°C, the centrifugation parameters are 5000 to 12000rpm, 10 to 30min; the dialysis molecular weight is 1000 to 10000Da.

[0007] (2) Preparation of carbon quantum dot tracer flooding agent

[0008] Take an appropriate amount of the above-synthesized carbon quantum dots and add them to the solution containing surfactant and skeleton monomer, stir well, then transfer to a three-necked flask, pass nitrogen for 30 minutes under ice-water bath conditions, add initiator to start the reaction, separate, purify and dry the above reaction solution after a period of time to obtain a carbon quantum dot tracer oil displacement mixture. During the reaction process, the temperature is guaranteed to be 60-80°C, and the reaction time is maintained at 2-6h; the surfactant includes one or more of dodecylbenzenesulfonic acid, polyvinylpyrrolidone K30, dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, trimethylchlorosilane, dodecylhydroxypropylsulfobetaine, γ-(methacryloyloxy)propyltrimethoxysilane; the skeleton monomer includes polyvinyl alcohol, polypropylene alcohol, diethanolamine, triethanolamine, propylene, butene, sodium dodecylbenzenesulfonate, dodecyl One or more of sodium benzene sulfonate, sodium tetradecylbenzene sulfonate, sodium hexadecylbenzene sulfonate, polydimethylsiloxane, polymethylhydrogensiloxane, and polymethylphenylsiloxane; the initiator includes one or two of benzoyl peroxide (BPO), sodium hydrogen peroxide, sodium peroxide, potassium peroxide, ammonium peroxide, di-tert-butyl sodium peroxide, sodium hydrogen sulfate, ammonium hydrogen sulfate, potassium hydrogen sulfate, and calcium hydrogen sulfate; the reagents used for the above separation and purification include one or two of pure water, ethanol, and acetone; the temperature of the drying process is maintained at 60-80°C. DETAILED DESCRIPTION

[0009] Below in conjunction with specific embodiment, the present invention is described in detail, the embodiment provided is only to set forth the present invention, rather than to limit the scope of the present invention.These scopes or values ​​should be construed as comprising values ​​approaching these range values.For numerical range, between the end point values ​​of each scope, between the end point values ​​of each scope and a separate point value, and between the separate point value can be combined with each other and obtain one or more new numerical ranges, and these numerical ranges should be considered as specifically disclosed in this article.

[0010] Example 1 Preparation of carbon quantum dot tracer, the preparation method specifically includes the following steps:

[0011] (1) Weigh 4 g of citric acid and 9 ml of 1,2-diaminoethane and dissolve them in 80 ml of pure water. Shake them in an ultrasonic cleaner for 10 min to make them completely mixed.

[0012] (2) transferring the solution in step (1) above into a high-temperature and high-pressure reactor with a polytetrafluoroethylene liner, and passing nitrogen gas for half an hour to remove the air in the reaction system;

[0013] (3) The reaction time was set to 10 h and the reaction temperature was set to 180°C. When the reaction time reached 2 h, 4 h, 6 h, and 8 h, 3 ml of sample was taken out from the sampling port respectively;

[0014] (4) After the reaction is completed, the product obtained in step (3) is centrifuged at 12000 rpm for 10 min to remove impurities in the lower layer;

[0015] (5) Transfer the sample obtained in step (4) to a 3400Da dialysis bag and dialyze for 20 hours;

[0016] (6) The dialysate in step (5) was placed in a freeze drying oven and dried for 24 hours, and then the powder product was collected.

[0017] Example 2 Preparation of a carbon quantum dot tracer oil displacement mixture, the preparation method specifically comprises the following steps:

[0018] (1) Dissolve 3.6 g of dodecylbenzenesulfonic acid in 34 ml of deionized water and stir to form a transparent solution.

[0019] (2) Weigh 2 g of the product obtained in Example 1 above and add it to the solution in step (1);

[0020] (3) Slowly add about 4.8 ml of triethanolamine into the solution and observe the change in turbidity of the solution until a relatively uniform solution is formed.

[0021] (4) Transfer the solution obtained in step (3) to a three-necked flask and place it in an ice-water bath and flow nitrogen for 30 min;

[0022] (5) The solution of step (4) was transferred to an oil bath and 0.05 g of potassium persulfate was added to start the reaction at a temperature of 60° C. for a reaction time of 4 h, with stirring being maintained during the reaction process;

[0023] (6) After the reaction is completed, the solution obtained in step (5) is cooled to room temperature and filtered through filter paper to remove unreacted impurities and precipitates.

[0024] (7) Washing: Use deionized water to wash the product to remove excess solvent and unreacted substances.

[0025] (8) Drying: The final product is dried in vacuum at 60° C. to obtain a dry carbon quantum dot tracer oil displacement mixture.

[0026] Example 3 Preparation of carbon quantum dot tracer, the preparation method specifically includes the following steps:

[0027] (1) Weigh 4.8 g of urea and 4.2 ml of acrylic acid and dissolve them in 60 ml of pure water. Shake them in an ultrasonic cleaner for 10 min to make them completely mixed.

[0028] (2) transferring the solution in step (1) above into a high-temperature and high-pressure reactor with a polytetrafluoroethylene liner, and passing nitrogen gas for half an hour to remove the air in the reaction system;

[0029] (3) The reaction time was set to 9 h and the reaction temperature was set to 200 °C. When the reaction time reached 2 h, 4 h, 6 h, and 8 h, 3 ml of sample was taken out from the sampling port respectively;

[0030] (4) After the reaction is completed, the product obtained in step (3) is centrifuged at 10,000 rpm for 20 min to remove impurities in the lower layer;

[0031] (5) Transfer the sample obtained in step (4) to a 3400Da dialysis bag and dialyze for 20 hours;

[0032] (6) The dialysate in step (5) was placed in a freeze drying oven and dried for 24 hours, and then the powder product was collected.

[0033] Example 4 Preparation of a carbon quantum dot tracer oil displacement mixture, the preparation method specifically comprises the following steps:

[0034] (1) 2.9 g of sodium hexadecylbenzenesulfonate was dissolved in 40 ml of a mixed solvent of ethanol / pure water and stirred to form a transparent solution.

[0035] (2) Weigh 2.4 g of dodecyl hydroxypropyl sulfobetaine and dissolve it in the solution of step (1).

[0036] (3) Add 0.8 g of the carbon quantum dots prepared in Example 3 to the solution of step (2) and shake for 30 minutes using an ultrasonic cleaner to ensure that the surfactant can be evenly adsorbed onto the surface of the carbon quantum dot tracer.

[0037] (4) The mixed solution obtained in step (3) was heated to 55° C., 0.04 g of ammonium persulfate was added and stirred for 3.5 h to uniformly distribute sodium hexadecylbenzenesulfonate and dodecylhydroxypropylsulfobetaine on the surface of the carbon quantum dots and modify the surface of the carbon quantum dot tracer.

[0038] (5) After the reaction is completed, the centrifuge speed is adjusted to 10,000 rpm and centrifuged for 30 minutes to obtain a carbon quantum dot tracer oil displacement mixture precipitate.

[0039] (6) The separated carbon quantum dot tracer oil displacement mixture is washed with deionized water for multiple times to remove unreacted surfactant and impurities.

[0040] (7) The product obtained in the above step (6) was low-temperature dried in a vacuum oven at 55° C. for 24 h to obtain a dry carbon quantum dot tracer oil displacement mixture.

Claims

1. A method for preparing a carbon quantum dot tracer oil displacement mixture, characterized in that: The preparation method is as follows: (1) after the carbon source and the solvent (the mass ratio of the carbon source to the solvent is 10% to 20%) are uniformly mixed, the mixture is transferred to a high-temperature and high-pressure reactor with a polytetrafluoroethylene liner, and nitrogen is passed through for half an hour to remove the air in the reaction system; (2) setting the reaction time to 2 to 12 h and the reaction temperature to 160 to 220 °C, and taking samples every 2 h; (3) After the reaction is completed, a large amount of impurities are removed by centrifugation (centrifugation parameters 5000-12000 rpm, 10-30 min), and then further purified by dialysis (dialysis molecular weight 1000-10000 Da), and finally dried using a freeze dryer to obtain a carbon quantum dot tracer; (4) adding an appropriate amount of the carbon quantum dot tracer synthesized above into a solution containing a surfactant and a backbone monomer, and stirring thoroughly; (5) Adjust the pH of the mixed solution, then transfer it to a three-necked flask, flow nitrogen for 30 min under ice-water bath conditions, add initiator (0.5-1.5%) to start the reaction (reaction temperature 40-60°C, reaction time 2-6 h); (6) After a period of time, the reaction solution is separated, purified, and dried to obtain a carbon quantum dot tracer oil displacement mixture.

2. The carbon quantum dot tracer prepared according to steps (1) to (3) of claim 1 is characterized in that The particle size distribution is between 6 and 8 nm, the fluorescence absorption peak is between 260 and 400 nm, and the fluorescence emission peak is between 400 and 600 nm.

3. The carbon quantum dot tracer oil displacement mixture prepared according to steps (3) to (6) of claim 1 is characterized in that Its surface wetting angle is between 90 and 140°.

4. The surface of the carbon quantum dot tracer displacement mixture prepared according to claim 1 has hydrophobicity. The carbon quantum dot tracer displacement mixture combines with oil molecules through its hydrophobic groups, destroying the tight structure of the oil-water interface, thereby reducing interfacial tension and promoting oil desorption and migration.

5. The method for preparing the carbon quantum dot tracer oil displacement mixture according to claim 1, characterized in that The preparation method includes the preparation of a carbon quantum dot tracer, surface modification of the carbon quantum dot tracer, and preparation of a carbon quantum dot tracer oil displacement mixture.

6. The preparation of the carbon quantum dot tracer according to claim 5, characterized in that The preferred carbon source material is one that can provide abundant oxygen-containing functional groups and amino groups in the hydrothermal reaction, so that the surface of the synthesized CQDs can be functionalized with amino groups and exhibit good water solubility and fluorescence properties.

7. The surface modification of the carbon quantum dot tracer according to claim 5, characterized in that The surfactant selected should have both a hydrophilic group and a hydrophobic main chain, and form a micellar structure and embed some hydrophobic molecules so that the overall system exhibits hydrophobicity.

8. The preparation of the carbon quantum dot tracer oil displacement mixture according to claim 5, characterized in that During the preparation process, the mass ratio of the surfactant to the carbon quantum dot tracer is maintained at 1.5-2, and the mass ratio of the skeleton monomer to the surfactant is maintained at 1-1.

5.

9. The method for preparing a carbon quantum dot tracer according to claim 5, characterized in that The reaction temperature and reaction time are set at 160℃~220℃. Higher temperature helps to accelerate the carbonization reaction and control the size of carbon quantum dots. Too high reaction temperature will lead to reduced fluorescence performance of the product. The reaction time is set at 2~12h. Longer reaction time can obtain smaller carbon quantum dots with better fluorescence performance.

10. The method for preparing a carbon quantum dot tracer according to claim 5, characterized in that During the synthesis process, samples were taken every 2 hours, and the appropriate reaction time was optimized through one reaction, thus reducing the experimental time cost.