Broadly distributed zirconium oxide-aminated carbon quantum dot nanofluids and their preparation and application

Abstract

The present invention discloses a wide-distribution zirconium oxide-aminated carbon quantum dot nanofluid and its preparation and application. The nanofluid comprises nano zirconium oxide, aminated carbon quantum dots and water, wherein the aminated carbon quantum dots comprise carbon quantum dots and polyethyleneimine connected to the carbon quantum dots via amide bonds; the solid content of the nanofluid is 0.001% to 0.2%. The particle size distribution of zirconium oxide-aminated carbon quantum dot composite nanoparticles is wide, and they can enter various small pore throats in the rock formation, comprehensively improving the swept volume of micro-voids, thereby improving the mining efficiency of low-permeability / ultra-low-permeability oil fields. Carbon quantum dots are modified with PEI, and amino groups are introduced on the surface of the carbon quantum dots. The aminated carbon quantum dots are positively charged in the nanofluid and can be used as a cationic surfactant to stabilize the nanofluid without the need for additional surfactants. At the same time, they form ion pairs with the carboxylic acid groups of crude oil, thereby better realizing the targeted oil exploration function.

Description

Technical Field

[0001] The present invention relates to the technical field of nano-oil displacement, and in particular to a broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid and its preparation and application. Background Art

[0002] Hydrocarbon fuels will remain the main energy source for human society for some time to come. Innovation in oil exploration and enhanced oil recovery (EOR) technology is a key focus of the oil and gas industry, with the goal of increasing the oil recovery rate from currently exploited reservoirs and unconventional oil and gas resources. Nanoparticles have great potential in the EOR field of low / ultra-low permeability reservoirs. Their advantages are: (1) they can be flexibly customized through combination and chemical modification; (2) their unique mechanical and thermal stability can withstand the harsh environmental conditions of underground reservoirs such as high temperature, high pressure, strong shear, and high salinity; (3) their interfacial activity can change the wettability of the rock surface, exfoliate the crude oil in the pore throat in the form of small oil droplets, and then displace it. Therefore, nanofluids prepared with water as the carrier and nanoparticles as the dispersed phase are ideal media for displacing low / ultra-low permeability reservoirs.

[0003] As a typical representative of zero-dimensional nanomaterials, carbon quantum dots (CQDs) are three-dimensionally located in the nanoscale range (1nm to 10nm) and possess unique physical and chemical properties. They are an emerging EOR technology that addresses the challenge of nanoscale pore-throat displacement. The Chemical Engineering Journal, Vol. 405, 2021, reported that a nanofluid containing 0.01 wt% CQDs was used to flood a tight limestone reservoir, increasing oil recovery by 17±0.2%. Under high-temperature and high-salinity conditions, CQDs exhibit strong colloidal stability. Studies of the CQD oil displacement mechanism revealed that, in addition to altering rock wettability, their small size temporarily blocks nanopore throats. As the displacement agent is continuously injected, the pressure surrounding the blocked pore throats increases, thereby improving the removal efficiency of the attached oil. As more trapped oil is removed, the pressure decreases, and the particle aggregates dissociate and redisperse into the nanofluid.

[0004] CN104531118A discloses an intelligent nano-oil-displacing agent. The main nanofluid component is selected from one or more of silica nanoparticles, silicon nanoparticles, calcium carbonate nanoparticles, calcium oxide nanoparticles, graphite powder, copper oxide nanoparticles, and zinc oxide nanoparticles. After surface modification with functional monomers, the agent is mixed with a surfactant and alkali to produce the intelligent nano-oil-displacing agent. The nanoparticles used are conventional materials and do not reach the size of quantum dots. All nanoparticles are surface-modified in a one-pot process. This eliminates the differences in the properties of different nanomaterials and their interactions with rock reservoirs and oil droplets, eliminating the need for additional surfactants, which increases the complexity of the system.

[0005] The nanofluid disclosed in CN110964491A consists primarily of polymer nanoparticles with a diameter of 10 to 1000 nm, produced directly in a medium via inverse microemulsion polymerization. The monomers and organic solvents used in the nanofluid preparation process are toxic and pose a risk to the environment. Injecting the polymer nanofluid underground also poses a risk of environmental pollution. The nanoparticles are larger than quantum dots and have a lower swept volume.

[0006] CN114956052A discloses a method for preparing carbon quantum dots. Using aldehyde and base as core raw materials, the nanofluid forms 1-10 nm carbon quantum dots through cross-linking polymerization. A capping agent is used to control the particle size of the carbon quantum dots, and an activator is used to enhance their interfacial activity. The nanofluid is a solution of single carbon quantum dots, lacking a stabilizer. This system results in the quantum dots easily agglomerating and resulting in a narrow particle size distribution. Summary of the Invention

[0007] The present invention aims to provide a broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid, as well as its preparation and application. This invention designs and prepares a novel nanofluid that achieves improved oil recovery. This invention addresses the inefficiency of water flooding in low-permeability and ultra-low-permeability reservoirs, as well as the complex processes, system complexity, environmental pollution, and small core micropore size associated with conventional nanofluid technology, thereby improving crude oil recovery efficiency.

[0008] In order to achieve the above objectives, the present invention adopts the following technical solutions:

[0009] The first aspect of the present invention provides a broad distribution zirconium oxide-aminated carbon quantum dot nanofluid, the nanofluid comprising nano zirconium oxide, aminated carbon quantum dots and water;

[0010] The solid content of the nanofluid is 0.001% to 0.2%; wherein the mass ratio of the nano zirconium oxide to the aminated carbon quantum dots is (3 to 5):3;

[0011] The aminated carbon quantum dots include carbon quantum dots and polyethyleneimine connected to the carbon quantum dots via amide bonds.

[0012] According to the nanofluid of the present invention, preferably, the aminated carbon quantum dots are obtained by amidation reaction between carboxyl carbon quantum dots and polyethyleneimine.

[0013] The carboxyl carbon quantum dots have carboxyl groups, and the polyethyleneimine (PEI) has amino groups. These two are connected by an amidation reaction to form an amide bond. In the resulting aminated carbon quantum dots, the quantum dots and polyethyleneimine (PEI) are connected by an amide bond (covalent bond). Covalent bonds are more stable than ionic and hydrogen bonds and can be used for oil recovery in high-temperature chemical environments in reservoirs.

[0014] According to the nanofluid of the present invention, preferably, the water is deionized water.

[0015] According to the nanofluid of the present invention, preferably, the particle size of the nano-zirconium oxide is in the range of 20 nm to 900 nm, more preferably in the range of 50 nm to 300 nm.

[0016] According to the nanofluid of the present invention, preferably, the particle size of the aminated carbon quantum dots is in the range of 2 nm to 10 nm, more preferably 5 nm to 10 nm.

[0017] According to the nanofluid of the present invention, preferably, the particle size of the nano-zirconium oxide is in the range of 50 nm to 300 nm, and the particle size of the aminated carbon quantum dots is in the range of 5 nm to 10 nm.

[0018] According to the nanofluid of the present invention, preferably, the solid content of the nanofluid is 0.01% to 0.2%.

[0019] The nano-zirconia with different particle sizes used in the present invention can be obtained through commercial purchase, and the carboxyl carbon quantum dots can also be obtained through commercial purchase, for example, from Xi'an Qiyue Biotechnology Co., Ltd.

[0020] According to the nanofluid of the present invention, preferably, the specific preparation process of the aminated carbon quantum dots includes:

[0021] Dispersing carboxyl carbon quantum dots in a reaction medium, adding a condensing agent and an active agent solution and stirring evenly; then adding a polyethyleneimine solution to react to obtain a solution containing the aminated carbon quantum dots;

[0022] The obtained solution is centrifuged, washed with water until neutral, and dried to obtain the aminated carbon quantum dots.

[0023] In the preparation process of the aminated carbon quantum dots of the present invention, preferably, the reaction medium is selected from at least one of deionized water, N,N-dimethylformamide, dimethyl sulfoxide, dichloromethane, tetrahydrofuran, tert-butyl methyl ether, cyclopentyl methyl ether, dimethyl carbonate, ethyl acetate, isopropanol, 2-methyltetrahydrofuran, 2-(N-morpholino)ethanesulfonic acid, acetonitrile, methanol, and ethanol.

[0024] In the preparation process of the aminated carbon quantum dots of the present invention, preferably, the reaction medium is deionized water.

[0025] In the preparation process of the aminated carbon quantum dots of the present invention, preferably, the condensing agent is selected from one of a carbodiimide condensing agent, an organophosphorus condensing agent, an onium salt condensing agent, and other condensing agents (3-acyl-2-thiothiazoline, tris(2,6-dimethoxyphenyl)bismuth, N,N'-carbonyldiimidazole, 4-(4,6-dimethoxytriazine-2-yl)-4-methylmorpholine hydrochloride).

[0026] The carbodiimide condensing agents include 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, dicyclohexylcarbodiimide, diisopropylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, O-(5-norbornene-2,3-dicarbonimide)-N,N,N',N'-tetramethyluronium tetrafluoroboric acid, etc.; the organophosphorus condensing agents include 2-(7-azobenzotriazole)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(benzotriazole-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, 6-chlorobenzotriazole-1,1,3,3-tetramethyluronium hexafluorophosphate, diphenylphosphoryl chloride, diethyl cyanide phosphoryl, diphenylphosphoryl azide, thiodimethylphosphoryl azide, di(2-oxy-3- The onium salt condensing agents include O-(7-azabenzotriazol-1-yl)-bis(tetrahydropyrrolyl)carbonium hexafluorophosphate, O-(benzotriazol-1-yl)-bis(tetrahydropyrrolyl)carbonium hexafluorophosphate, O-(benzotriazol-1-yl)-bis(dimethylamino)carbonium hexafluorophosphate, ) carbonium tetrafluoroborate, O-(N-succinimidyl)-bis(dimethylamino)carbonium tetrafluoroborate, benzotriazol-1-yloxy-tris(dimethylamino)phosphonium hexafluorophosphate, benzotriazol-1-yloxy-tris(tetrahydropyrrolyl)phosphonium hexafluorophosphate, (3H-1,2,3-triazolo[4,5-b]pyridine-3-oxy)tris-1-pyrrolidinyl hexafluorophosphate, etc.

[0027] In the preparation process of the aminated carbon quantum dots of the present invention, preferably, the condensing agent is dimethylaminopropylethylcarbodiimide hydrochloride.

[0028] In the preparation process of the aminated carbon quantum dots of the present invention, preferably, the active agent is selected from one of N-hydroxysuccinimide, 4-dimethylaminopyridine, 4-pyrrolidinopyridine, 1-hydroxybenzotriazole, 1-hydroxy-7-azobenzotriazole, N-hydroxysuccinimide, N-hydroxyphthalimide, pentafluorophenol, triethylamine, diazabicycle, and pyridine.

[0029] In the preparation process of the aminated carbon quantum dots of the present invention, preferably, the active agent is N-hydroxysuccinimide.

[0030] In the preparation process of the aminated carbon quantum dots of the present invention, preferably, the solvent of the polyethyleneimine solution is the same as the reaction medium, preferably deionized water; the concentration of the polyethyleneimine solution is 2% to 50%, more preferably 5% to 20%.

[0031] In the preparation process of the aminated carbon quantum dots of the present invention, preferably, the polyethyleneimine is selected from at least one of linear polyethyleneimine and branched polyethyleneimine, and the molecular weight of the polyethyleneimine is 1500 to 20000, more preferably 8000 to 18000.

[0032] In the preparation process of the aminated carbon quantum dots of the present invention, preferably, the molar ratio of the carboxyl carbon quantum dots, the condensing agent, the activating agent and the polyethyleneimine is 1:(1-2):(1-2):1.

[0033] More preferably, the molar ratio of the carboxyl carbon quantum dots, the condensing agent, the activating agent and the polyethyleneimine is 1:1.5:1.5:1.

[0034] In the preparation process of the aminated carbon quantum dots of the present invention, preferably, the reaction temperature is -30°C to 40°C; more preferably, 0°C to 25°C.

[0035] In the preparation process of the aminated carbon quantum dots of the present invention, preferably, the reaction time is 2 hours to 24 hours; more preferably, 12 hours to 24 hours.

[0036] In the preparation process of the aminated carbon quantum dots of the present invention, preferably, the centrifugal speed is 20,000 rpm to 150,000 rpm; more preferably, 25,000 rpm to 30,000 rpm.

[0037] In the preparation process of the aminated carbon quantum dots of the present invention, preferably, the drying temperature is room temperature.

[0038] The second aspect of the present invention provides a method for preparing at least one zirconium oxide-aminated carbon quantum dot nanofluid, which comprises dispersing nano zirconium oxide and aminated carbon quantum dots in water to obtain the zirconium oxide-aminated carbon quantum dot nanofluid.

[0039] A third aspect of the present invention provides one or more applications of zirconium oxide-aminated carbon quantum dot nanofluids in water flooding of low permeability / ultra-low permeability oil reservoirs.

[0040] The beneficial effects of the present invention include:

[0041] 1) This invention uses zirconium oxide and carbon quantum dot composite nanoparticles as the main component of the nanofluid for the first time, comprehensively utilizing the high rock surface wettability reversal characteristics of nano zirconium oxide and the small size characteristics of carbon quantum dots to expand the swept volume while enhancing the oil displacement efficiency.

[0042] 2) Zirconia-aminated carbon quantum dot composite nanoparticles have a wide particle size distribution and can penetrate into various tiny pore throats in the rock formation, comprehensively increasing the swept volume of tiny voids, thereby improving the extraction efficiency of low / ultra-low permeability oil fields.

[0043] 3) PEI is used to modify carbon quantum dots and amino groups are introduced on the surface of carbon quantum dots. The reaction process is mild, and the aminated carbon quantum dots are positively charged in the nanofluid. They can act as cationic surfactants to stabilize the nanofluid without the need for additional surfactants. At the same time, they form ion pairs with the carboxylic acid groups of crude oil, thereby better realizing the targeted oil search function.

[0044] To address the current challenges of poor water flooding in low- and ultra-low-permeability reservoirs, as well as the development and application of conventional nanoscale flooding technologies, this invention combines nanozirconia with aminated carbon quantum dots and disperses them in deionized water. This method, without the addition of a surfactant, produces a nanofluid with broad distribution, self-stability, and high conformance volume. Core flooding experiments have demonstrated that this broadly distributed zirconia-aminated carbon quantum dot nanofluid effectively reduces injection pressure, enhancing injection pressure and significantly improving oil recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the zirconium oxide-aminated carbon quantum dot nanofluid of the present invention.

[0046] Figure 2 This is the infrared spectrum of the aminated carbon quantum dots prepared in Example 1 of the present invention. The infrared spectra of other examples are the same.

[0047] Figure 3 This is a transmission electron microscope photograph of the aminated carbon quantum dots prepared in Example 1 of the present invention.

[0048] Figure 4 This is the particle size distribution diagram of nano zirconium oxide in Example 1 of the present invention. DETAILED DESCRIPTION

[0049] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. Those skilled in the art should understand that the following specific description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0050] like Figure 1 As shown, the zirconium oxide-aminated carbon quantum dot nanofluid provided by the present invention comprises nano-zirconium oxide, aminated carbon quantum dots, and water. The aminated carbon quantum dots comprise carbon quantum dots and polyethyleneimine connected to the carbon quantum dots via amide bonds. The nano-zirconium oxide has a particle size range of 20 nm to 900 nm, and the aminated carbon quantum dots have a particle size range of 2 nm to 10 nm. The zirconium oxide-aminated carbon quantum dot composite nanoparticles have a wide particle size distribution and can penetrate into various tiny pore throats within rock formations, comprehensively increasing the swept volume of micro-voids and thereby improving the recovery efficiency of low-permeability / ultra-low-permeability oil fields.

[0051] PEI is used to modify carbon quantum dots and amino groups are introduced on the surface of carbon quantum dots. The reaction process is mild, and the aminated carbon quantum dots are positively charged in nanofluids. They can be used as cationic surfactants to stabilize nanofluids without the need for additional surfactants. At the same time, they form ion pairs with the carboxylic acid groups of crude oil, thereby better realizing the targeted oil search function.

[0052] Specifically, the solid content of the nanofluid is 0.001% to 0.2%, preferably 0.01% to 0.2%; wherein the mass ratio of the nano-zirconium oxide to the aminated carbon quantum dots is (3-5):3.

[0053] In some specific embodiments of the present invention, the particle size of the nano-zirconium oxide is in the range of 50 nm to 300 nm, and the particle size of the aminated carbon quantum dots is in the range of 5 nm to 10 nm.

[0054] In some specific embodiments of the present invention, the aminated carbon quantum dots are obtained by an amidation reaction between carboxyl carbon quantum dots and polyethyleneimine. The carboxyl carbon quantum dots have carboxyl groups, and the polyethyleneimine (PEI) has amino groups, and the two are connected by an amidation reaction to form an amide bond; in the resulting aminated carbon quantum dots, the quantum dots and polyethyleneimine (PEI) are connected by an amide bond (covalent bond). Covalent bonds are more stable than ionic bonds and hydrogen bonds and can be used for oil recovery in high-temperature chemical environments of reservoirs. Preferably, the water is deionized water.

[0055] The nano-zirconia with different particle sizes used in the present invention can be obtained through commercial purchase, and the carboxyl carbon quantum dots can also be obtained through commercial purchase, for example, from Xi'an Qiyue Biotechnology Co., Ltd.

[0056] In some specific embodiments of the present invention, the specific preparation process of the aminated carbon quantum dots includes:

[0057] Dispersing carboxyl carbon quantum dots in a reaction medium, adding a condensing agent and an active agent solution and stirring evenly; then adding a polyethyleneimine solution to react to obtain a solution containing the aminated carbon quantum dots;

[0058] The obtained solution is centrifuged, washed with water until neutral, and dried at room temperature to obtain the aminated carbon quantum dots.

[0059] In some specific embodiments of the present invention, the reaction medium is selected from at least one of deionized water, N,N-dimethylformamide, dimethyl sulfoxide, dichloromethane, tetrahydrofuran, tert-butyl methyl ether, cyclopentyl methyl ether, dimethyl carbonate, ethyl acetate, isopropanol, 2-methyltetrahydrofuran, 2-(N-morpholino)ethanesulfonic acid, acetonitrile, methanol, and ethanol; preferably deionized water.

[0060] In some specific embodiments of the present invention, the condensing agent is selected from a carbodiimide condensing agent, an organophosphorus condensing agent, an onium salt condensing agent and other condensing agents.

[0061] The carbodiimide condensing agents include 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, dicyclohexylcarbodiimide, diisopropylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, O-(5-norbornene-2,3-dicarbonimide)-N,N,N',N'-tetramethyluronium tetrafluoroboric acid, etc.; the organophosphorus condensing agents include 2-(7- Azobenzotriazole)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(benzotriazole-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, 6-chlorobenzotriazole-1,1,3,3-tetramethyluronium hexafluorophosphate, diphenylphosphoryl chloride, diethyl cyanophosphate, diphenylphosphoryl azide (DPPA), dimethylthiophosphoryl azide, di(2-oxygen -3-oxazolidinyl) phosphoryl chloride, triphenylphosphine-polyhalomethane, triphenylphosphine-hexachloroacetone, triphenylphosphine-NBS, etc.; the onium salt condensing agent includes O-(7-azabenzotriazol-1-yl)-bis(tetrahydropyrrolyl)carbonium hexafluorophosphate, O-(benzotriazol-1-yl)-bis(tetrahydropyrrolyl)carbonium hexafluorophosphate, O-(benzotriazol-1-yl)-bis(dimethyl The condensing agent includes benzotriazole-1-yloxy-tris(dimethylamino)phosphonium hexafluorophosphate, benzotriazole-1-yloxy-tris(tetrahydropyrrolyl)phosphonium hexafluorophosphate, (3H-1,2,3-triazolo[4,5-b]pyridine-3-oxy)tri-1-pyrrolidinyl hexafluorophosphate, etc. The other condensing agents include (3-acyl-2-thiothiazoline, tris(2,6-dimethoxyphenyl)bismuth, N,N'-carbonyldiimidazole, 4-(4,6-dimethoxytriazine-2-yl)-4-methylmorpholine hydrochloride, etc. Preferably, the condensing agent is dimethylaminopropylethylcarbodiimide hydrochloride.

[0062] In some specific embodiments of the present invention, the active agent is selected from one of N-hydroxysuccinimide, 4-dimethylaminopyridine, 4-pyrrolidinylpyridine, 1-hydroxybenzotriazole, 1-hydroxy-7-azobenzotriazole, N-hydroxysuccinimide, N-hydroxyphthalimide, pentafluorophenol, triethylamine, diazabicycle, and pyridine; preferably N-hydroxysuccinimide.

[0063] In some specific embodiments of the present invention, the solvent of the polyethyleneimine solution is the same as the reaction medium, preferably deionized water; the concentration of the polyethyleneimine solution is 2% to 50%, more preferably 5% to 20%.

[0064] In some specific embodiments of the present invention, the polyethyleneimine is selected from at least one of linear polyethyleneimine and branched polyethyleneimine, and the molecular weight of the polyethyleneimine is 1,500 to 20,000, more preferably 8,000 to 18,000.

[0065] In some specific embodiments of the present invention, the molar ratio of the carboxyl carbon quantum dots, the condensing agent, the activating agent and the polyethyleneimine is 1:(1-2):(1-2):1; preferably 1:1.5:1.5:1.

[0066] In some specific embodiments of the present invention, the reaction temperature is -30°C to 40°C; preferably 0°C to 25°C.

[0067] In some specific embodiments of the present invention, the reaction time is 2 hours to 24 hours, preferably 12 hours to 24 hours.

[0068] In some specific embodiments of the present invention, the centrifugal speed is 20,000 rpm to 150,000 rpm, preferably 25,000 rpm to 30,000 rpm.

[0069] In some specific embodiments of the present invention, the drying temperature is room temperature.

[0070] The preparation method of the above-mentioned zirconium oxide-aminated carbon quantum dot nanofluid comprises dispersing nano-zirconium oxide and aminated carbon quantum dots in water to obtain the zirconium oxide-aminated carbon quantum dot nanofluid. This nanofluid can be used in water flooding of low-permeability and ultra-low-permeability oil reservoirs. Core flooding experiments have verified that the broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid prepared by the present invention can effectively reduce injection pressure, thereby achieving a pressure-reducing and injection-increasing effect, and significantly improving oil recovery.

[0071] The following provides specific examples for illustration:

[0072] All numerical values ​​in the examples (e.g., temperature, time, concentration, and weight, including ranges for each thereof) are generally approximate values ​​that may be varied (+) or (-) in increments of 0.1 or 1.0, as appropriate. All numerical values ​​are to be understood as being preceded by the term "about."

[0073] The concentration of the PEI solution used in the following examples is 10%. The polyethyleneimine is linear polyethyleneimine, and the molecular weight of the polyethyleneimine is 1500, 8000, 12000, or 18000.

[0074] Example 1

[0075] This embodiment prepares a broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid, comprising the following steps:

[0076] S1. Disperse 0.2 mol of carboxyl carbon quantum dots in deionized water, add 0.3 mol of dimethylaminopropylethylcarbodiimide hydrochloride and 0.3 mol of N-hydroxysuccinimide solution, and stir evenly.

[0077] S2. Add 0.2 mol of PEI aqueous solution with a molecular weight of 8000 to the solution obtained in step S1, and stir at 25° C. for 24 hours to obtain a solution containing the aminated carbon quantum dots.

[0078] S3. The solution obtained in step S2 was centrifuged at a speed of 25000 rpm, the centrifuged product was collected, washed with water until neutral, and dried at room temperature to obtain aminated carbon quantum dots with an average particle size of 5 nm.

[0079] like Figure 2 As shown in the infrared spectrum of the aminated carbon quantum dots prepared by the present invention, 3415 cm -1 The absorption peak at 1619 cm is caused by the NH stretching vibration absorption peak in the amide group; -1 The absorption peaks at 4 and 5 are the stretching vibration peaks of the carbonyl C=O in the amide group. These two strong absorption peaks confirm the presence of amide groups on the surface of carbon quantum dots.

[0080] Figure 3 This is a transmission electron microscope photo of aminated carbon quantum dots. Figure 3 It can be seen that the aminated carbon quantum dots are in uniform granular form, have good dispersion, no adhesion, and have a particle size of 2 nm to 8 nm, with an average particle size of 5 nm.

[0081] S4. Disperse 0.05 g of nano-zirconium oxide with a particle size of 300 nm and 0.05 g of the aminated carbon quantum dots obtained in step S3 into 1 L of deionized water to obtain a widely distributed zirconium oxide-aminated carbon quantum dot nanofluid.

[0082] Figure 4 is the particle size distribution of the nano-zirconia used, Figure 4 It can be seen that the particle size distribution of nano-zirconia is narrow, which is consistent with Figure 3 By compounding the aminated carbon quantum dots shown, wide-distributed composite particles with a particle size of 2 nm to 300 nm can be obtained.

[0083] Example 2

[0084] This embodiment prepares a broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid, comprising the following steps:

[0085] S1. Disperse 0.2 mol of carboxyl carbon quantum dots in dichloromethane, add 0.3 mol of N,N'-carbonyldiimidazole HCl solution and 0.3 mol of diazabicyclo and stir evenly.

[0086] S2, adding 0.2 mol of PEI dichloromethane solution with a molecular weight of 12000 to the solution obtained in step S1, stirring at 25° C. for 24 hours to obtain a solution containing the aminated carbon quantum dots;

[0087] S3. The solution obtained in step S2 was centrifuged at a speed of 30,000 rpm, the centrifuged product was collected, washed with water until neutral, and dried at room temperature to obtain aminated carbon quantum dots with an average particle size of 6 nm.

[0088] S4. Disperse 0.03 g of nano-zirconium oxide with a particle size of 500 nm, 0.02 g of nano-zirconium oxide with a particle size of 300 nm, and 0.05 g of the aminated carbon quantum dots obtained in step S3 into 1 L of deionized water to obtain a widely distributed zirconium oxide-aminated carbon quantum dot nanofluid.

[0089] Example 3

[0090] This embodiment prepares a broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid, comprising the following steps:

[0091] S1. Disperse 0.2 mol of carboxyl carbon quantum dots in dichloromethane, add 0.25 mol of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide solution and 0.25 mol of 1-hydroxybenzotriazole solution, and stir evenly.

[0092] S2. Add 0.2 mol of PEI dichloromethane solution with a molecular weight of 18,000 to the solution obtained in step S1, and stir at 25° C. for 10 hours to obtain a solution containing the aminated carbon quantum dots.

[0093] S3. The solution obtained in step S2 was centrifuged at a speed of 35000 rpm, the centrifuged product was collected, washed with water until neutral, and dried at room temperature to obtain aminated carbon quantum dots with an average particle size of 8 nm.

[0094] S4. Disperse 0.05 g of nano-zirconium oxide with a particle size of 600 nm and 0.05 g of the aminated carbon quantum dots obtained in step S3 into 1 L of deionized water to obtain a widely distributed zirconium oxide-aminated carbon quantum dot nanofluid.

[0095] Example 4

[0096] This embodiment prepares a broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid, comprising the following steps:

[0097] S1. Disperse 0.2 mol of carboxyl carbon quantum dots in ethyl acetate, add 0.25 mol of diphenylphosphoryl chloride and 0.25 mol of triethylamine, and stir evenly.

[0098] S2. Add 0.2 mol of PEI dichloromethane solution with a molecular weight of 18,000 to the solution obtained in step S1, and stir at 0° C. for 10 h to obtain a solution containing the aminated carbon quantum dots.

[0099] S3. The solution obtained in step S2 was centrifuged at a speed of 35000 rpm, the centrifuged product was collected, washed with water until neutral, and dried at room temperature to obtain aminated carbon quantum dots with an average particle size of 10 nm.

[0100] S4. Disperse 0.05 g of nano-zirconium oxide with a particle size of 900 nm and 0.05 g of the aminated carbon quantum dots obtained in step S3 into 1 L of deionized water to obtain a widely distributed zirconium oxide-aminated carbon quantum dot nanofluid.

[0101] Example 5

[0102] This embodiment prepares a broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid, comprising the following steps:

[0103] S1. Disperse 0.2 mol of carboxyl carbon quantum dots in ethanol, add 0.25 mol of triphenylphosphine-tetrabromomethane and 0.25 mol of triethylamine and stir evenly.

[0104] S2. Add 0.2 mol of PEI ethanol solution with a molecular weight of 18,000 to the solution obtained in step S1, and stir at 25° C. for 2 h to obtain a solution containing the aminated carbon quantum dots.

[0105] S3. The solution obtained in step S2 was centrifuged at a speed of 35000 rpm, the centrifuged product was collected, washed with water until neutral, and dried at room temperature to obtain aminated carbon quantum dots with an average particle size of 5 nm.

[0106] S4. Disperse 0.005 g of nano-zirconium oxide with a particle size of 20 nm and 0.005 g of the aminated carbon quantum dots obtained in step S3 into 1 L of deionized water to obtain a widely distributed zirconium oxide-aminated carbon quantum dot nanofluid.

[0107] Example 6

[0108] This embodiment prepares a broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid, comprising the following steps:

[0109] S1. Disperse 0.2 mol of carboxyl carbon quantum dots in dichloromethane, add 0.25 mol of triphenylphosphine-NBS and 0.25 mol of pyridine, and stir evenly.

[0110] S2. Add 0.2 mol of PEI dichloromethane solution with a molecular weight of 18,000 to the solution obtained in step S1, stir at -30°C for 4 hours, and warm to room temperature to obtain a solution containing the aminated carbon quantum dots.

[0111] S3. The solution obtained in step S2 was centrifuged at a speed of 35000 rpm, the centrifuged product was collected, washed with water until neutral, and dried at room temperature to obtain aminated carbon quantum dots with an average particle size of 5 nm.

[0112] S4. Disperse 1.5 g of nano-zirconium oxide with a particle size of 50 nm and 0.5 g of the aminated carbon quantum dots obtained in step S3 into 1 L of deionized water to obtain a widely distributed zirconium oxide-aminated carbon quantum dot nanofluid.

[0113] Example 7

[0114] This embodiment prepares a broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid, comprising the following steps:

[0115] S1. Disperse 0.2 mol of carboxyl carbon quantum dots in N,N-dimethylformamide, add 0.4 mol of dicyclohexylcarbodiimide solution and 0.4 mol of 4-dimethylaminopyridine solution, and stir evenly.

[0116] S2, adding 0.2 mol of PEI with a molecular weight of 18,000 in N,N-dimethylformamide to the solution obtained in step S1, and stirring at 25° C. for 24 hours to obtain a solution containing the aminated carbon quantum dots;

[0117] S3. The solution obtained in step S2 was centrifuged at a speed of 35000 rpm, the centrifuged product was collected, washed with water until neutral, and dried at room temperature to obtain aminated carbon quantum dots with an average particle size of 8 nm.

[0118] S4. Disperse 0.05 g of nano-zirconium oxide with a particle size of 600 nm and 0.0375 g of the aminated carbon quantum dots obtained in step S3 into 1 L of deionized water to obtain a widely distributed zirconium oxide-aminated carbon quantum dot nanofluid.

[0119] Example 8

[0120] This embodiment prepares a broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid, comprising the following steps:

[0121] S1. Disperse 0.2 mol of carboxyl carbon quantum dots in N,N-dimethylformamide, add 0.3 mol of diisopropylcarbodiimide and 0.3 mol of 1-hydroxybenzotriazole solution and stir evenly.

[0122] S2. Add 0.2 mol of PEI with a molecular weight of 18,000 in N,N-dimethylformamide to the solution obtained in step S1, and stir at 25° C. for 10 hours to obtain a solution containing the aminated carbon quantum dots.

[0123] S3. The solution obtained in step S2 was centrifuged at a speed of 35000 rpm, the centrifuged product was collected, washed with water until neutral, and dried at room temperature to obtain aminated carbon quantum dots with an average particle size of 8 nm.

[0124] S4. Disperse 0.05 g of nano-zirconium oxide with a particle size of 600 nm and 0.03 g of the aminated carbon quantum dots obtained in step S3 into 1 L of deionized water to obtain a widely distributed zirconium oxide-aminated carbon quantum dot nanofluid.

[0125] Example 9

[0126] This embodiment prepares a broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid, comprising the following steps:

[0127] S1. Disperse 0.2 mol of carboxyl carbon quantum dots in acetonitrile, add 0.25 mol of benzotriazole-1-yloxy-tris(dimethylamino)phosphonium hexafluorophosphate and 0.25 mol of triethylamine, and stir evenly.

[0128] S2. Add 0.3 mol of PEI with a molecular weight of 18,000 in acetonitrile to the solution obtained in step S1, and stir at 25° C. for 2 h to obtain a solution containing the aminated carbon quantum dots.

[0129] S3. The solution obtained in step S2 was centrifuged at a speed of 35000 rpm, the centrifuged product was collected, washed with water until neutral, and dried at room temperature to obtain aminated carbon quantum dots with an average particle size of 8 nm.

[0130] S4. Disperse 0.03 g of nano-zirconium oxide with a particle size of 600 nm and 0.05 g of the aminated carbon quantum dots obtained in step S3 into 1 L of deionized water to obtain a widely distributed zirconium oxide-aminated carbon quantum dot nanofluid.

[0131] Example 10

[0132] This embodiment prepares a broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid, comprising the following steps:

[0133] S1. Disperse 0.2 mol of carboxyl carbon quantum dots in N,N-dimethylformamide, add 0.25 mol of benzotriazol-1-yloxy-tris(tetrahydropyrrolyl)phosphonium hexafluorophosphate and 0.25 mol of 1-hydroxybenzotriazole solution and stir evenly.

[0134] S2. Add 0.2 mol of PEI with a molecular weight of 18,000 in N,N-dimethylformamide to the solution obtained in step S1, and stir at 25° C. for 2 h to obtain a solution containing the aminated carbon quantum dots.

[0135] S3. The solution obtained in step S2 was centrifuged at a speed of 35000 rpm, the centrifuged product was collected, washed with water until neutral, and dried at room temperature to obtain aminated carbon quantum dots with an average particle size of 8 nm.

[0136] S4. Disperse 0.05 g of nano-zirconium oxide with a particle size of 600 nm and 0.025 g of the aminated carbon quantum dots obtained in step S3 into 1 L of deionized water to obtain a widely distributed zirconium oxide-aminated carbon quantum dot nanofluid.

[0137] Example 11

[0138] This embodiment prepares a broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid, comprising the following steps:

[0139] S1. Disperse 0.2 mol of carboxyl carbon quantum dots in N,N-dimethylformamide, add 0.25 mol of O-(N-succinimidyl)-bis(dimethylamino)carbonium tetrafluoroborate and 0.25 mol of 1-hydroxybenzotriazole solution and stir evenly.

[0140] S2. Add 0.2 mol of PEI with a molecular weight of 1500 in N,N-dimethylformamide to the solution obtained in step S1, and stir at 40° C. for 4 h to obtain a solution containing the aminated carbon quantum dots.

[0141] S3. The solution obtained in step S2 was centrifuged at a speed of 35000 rpm, the centrifuged product was collected, washed with water until neutral, and dried at room temperature to obtain aminated carbon quantum dots with an average particle size of 5 nm.

[0142] S4. Disperse 0.05 g of nano-zirconium oxide with a particle size of 600 nm and 0.05 g of the aminated carbon quantum dots obtained in step S3 into 1 L of deionized water to obtain a widely distributed zirconium oxide-aminated carbon quantum dot nanofluid.

[0143] Comparative Example 1

[0144] This comparative example provides a narrow distribution aminated carbon quantum dot nanofluid, comprising the following steps:

[0145] 0.1 g of the aminated carbon quantum dots obtained in step S3 of Example 1 was dispersed into 1 L of deionized water to obtain an aminated carbon quantum dot nanofluid with a narrow distribution.

[0146] Test Example 1

[0147] The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid obtained in Examples 1-11 and the narrow distribution aminated carbon quantum dot nanofluid obtained in Comparative Example 1 were subjected to oil recovery tests.

[0148] The oil recovery test process is as follows:

[0149] Low-permeability outcrop sandstone cores (core length: 5.0 cm; core diameter: 2.5 cm; gas permeability: 10.3 mD) were dried and weighed at room temperature, saturated with simulated formation water under vacuum for 8 hours, allowed to stand for 24 hours, and weighed again. Porosity and pore volume were calculated. The cores were saturated with oil at a constant temperature of 55°C, and the saturated crude oil volume was calculated. The cores were then aged for 48 hours. Nanofluid flooding was performed on the cores at a flow rate of 0.2 mL / min until the water cut reached 98%. The produced oil volume was recorded, and the water flooding recovery factor (produced oil volume divided by saturated crude oil volume) was calculated. The recovery factor data are shown in Table 1.

[0150] Table 1 Nanofluid recovery efficiency data

[0151]

[0152]

[0153] As can be seen from Table 1, the broadly distributed zirconium oxide-aminated carbon quantum dots prepared in this example demonstrate significant effectiveness in improving oil recovery in low-permeability reservoirs, nearly doubling the maximum recovery rate compared to water flooding alone. Compared to the narrowly distributed aminated carbon quantum dot nanofluid flooding of Comparative Example 1, the addition of large-particle nanozirconia effectively increases the swept volume of the nanofluid in pore throats of varying sizes, significantly improving the recovery rate. Furthermore, the nanofluid prepared using only nanozirconia is unstable, requiring the addition of a surfactant.

[0154] Within the defined ratio of zirconia nanoparticles to aminated quantum dots, the recovery rate decreases as the mass fraction of aminated quantum dots decreases, maintaining a fixed zirconia nanoparticle loading. This suggests that aminated quantum dots have a strong ability to dislodge oil adhering to ultrafine pore throats, and reducing the mass fraction of aminated quantum dots reduces overall oil displacement. Further reducing the mass fraction of aminated quantum dots beyond the defined ratio causes the system to lose stability due to the decrease in cationic surfactant concentration, leading to a significant drop in oil displacement. Similarly, maintaining a fixed aminated quantum dot loading and reducing the mass fraction of zirconia nanoparticles beyond the defined ratio also results in a significant drop in recovery due to the reduced ability of the nanofluid to dislodge oil adhering to large pore throats.

[0155] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid, wherein: The nanofluid consists of nano zirconium oxide, aminated carbon quantum dots and water; The aminated carbon quantum dots are obtained by an amidation reaction between carboxyl carbon quantum dots and polyethyleneimine.

2. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 1, wherein: The solid content of the nanofluid is 0.001% to 0.2%; wherein the mass ratio of the nano zirconium oxide to the aminated carbon quantum dots is (3 to 5):

3.

3. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 1, wherein: The particle size of the nano zirconium oxide ranges from 20 nm to 900 nm.

4. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 1, wherein: The particle size of the aminated carbon quantum dots ranges from 2 nm to 10 nm.

5. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 1, wherein: The particle size of the nano zirconium oxide is in the range of 50 nm to 300 nm; The particle size of the aminated carbon quantum dots ranges from 5 nm to 10 nm.

6. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 1, wherein: The solid content of the nanofluid is 0.01% to 0.2%.

7. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 1, wherein: The specific preparation process of the aminated carbon quantum dots includes: Dispersing carboxyl carbon quantum dots in a reaction medium, adding a condensing agent and an active agent solution and stirring evenly; then adding a polyethyleneimine solution to react to obtain a solution containing the aminated carbon quantum dots; The obtained solution is centrifuged, washed with water until neutral, and dried to obtain the aminated carbon quantum dots; The active agent is selected from one of N-hydroxysuccinimide, 4-dimethylaminopyridine, 4-pyrrolidinylpyridine, 1-hydroxybenzotriazole, 1-hydroxy-7-azobenzotriazole, N-hydroxysuccinimide, N-hydroxyphthalimide, pentafluorophenol, triethylamine, diazabicycle, and pyridine.

8. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 7, wherein: The reaction medium is selected from at least one of deionized water, N,N-dimethylformamide, dimethyl sulfoxide, dichloromethane, tetrahydrofuran, tert-butyl methyl ether, cyclopentyl methyl ether, dimethyl carbonate, ethyl acetate, isopropanol, 2-methyltetrahydrofuran, 2-(N-morpholino)ethanesulfonic acid, acetonitrile, methanol, and ethanol.

9. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 7, wherein: The reaction medium is deionized water.

10. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 7, wherein: The condensing agent is selected from the group consisting of carbodiimide condensing agents, organophosphorus condensing agents, onium salt condensing agents, 3-acyl-2-thiothiazoline, tris(2,6-dimethoxyphenyl)bismuth, N,N'-carbonyldiimidazole, and 4-(4,6-dimethoxytriazine-2-yl)-4-methylmorpholine hydrochloride.

11. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 7, wherein: The condensing agent is dimethylaminopropylethylcarbodiimide hydrochloride.

12. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 7, wherein: The active agent is N-hydroxysuccinimide.

13. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 7, wherein: The polyethyleneimine is selected from at least one of linear polyethyleneimine and branched polyethyleneimine, and the molecular weight of the polyethyleneimine is 1,500 to 20,000.

14. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 7, wherein: The molar ratio of the carboxyl carbon quantum dots, the condensing agent, the activating agent and the polyethyleneimine is 1:(1-2):(1-2):

1.

15. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 7, wherein: The molar ratio of the carboxyl carbon quantum dots, the condensing agent, the active agent and the polyethyleneimine is 1:1.5:1.5:

1.

16. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 7, wherein: The reaction temperature is -30°C to 40°C.

17. The broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to claim 7, wherein: The reaction time is 2h to 24h.

18. A method for preparing the broad distribution zirconium oxide-aminated carbon quantum dot nanofluid according to any one of claims 1 to 17, wherein: The preparation method comprises: dispersing nano zirconium oxide and aminated carbon quantum dots in water to obtain the broad-distribution zirconium oxide-aminated carbon quantum dot nanofluid.

19. Use of the broadly distributed zirconium oxide-aminated carbon quantum dot nanofluid according to any one of claims 1 to 17 in water flooding of low permeability / ultra-low permeability oil reservoirs.

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