Amphiphilic carbon dots, carbon nanofluids and their applications

Abstract

The present invention provides amphiphilic carbon dots, carbon nanofluids, and their applications, belonging to the field of nanomaterial oil recovery technology. The amphiphilic carbon dots are prepared by a solvothermal reaction of alkylphenol polyoxyethylene ethers and glucose as raw materials; the alkylphenol polyoxyethylene ethers include octylphenol polyoxyethylene ethers and / or nonylphenol polyoxyethylene ethers; and the mass ratio of the alkylphenol polyoxyethylene ethers to the glucose is 1:(0.1-2). The present invention utilizes alkylphenol polyoxyethylene ethers and glucose as raw materials to facilitate the preparation of amphiphilic carbon dots with high surface and interfacial activity. The amphiphilic carbon dots provided by the present invention exhibit excellent surface and interfacial activity at high temperatures and high salinity. The carbon nanofluid provided by the present invention is a compound of amphiphilic carbon dots and zwitterionic surfactants, which can further enhance the stability of the carbon nanofluid oil recovery system under high temperature and high salinity conditions, improve crude oil recovery, and achieve efficient production enhancement in deep reservoirs with high temperature and high salinity.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterial oil displacement, and in particular to an amphiphilic carbon dot, a carbon nanofluid and applications thereof. Background Art

[0002] Surfactants play a crucial role in oil and gas field development. With the exploration and development of deep and ultra-deep oil and gas reservoirs, the high temperature and high salinity of these formations pose greater challenges to the enhanced oil recovery (ER) performance of oil displacement agents. Sulfonic and benzene ring groups are often added to surfactant molecules to improve their temperature resistance. For example, surfactants such as petroleum sulfonates and alkylbenzene sulfonates, which are widely used in tertiary oil recovery, have excellent thermal stability, but their salt tolerance is poor. Zwitterionic surfactants, due to their excellent salt tolerance, are widely used in the development of high-salinity reservoirs.

[0003] Nanomaterials, due to their unique chemical structure and physicochemical properties, often exhibit excellent resistance to high temperatures and high salinity. Currently, nanomaterials commonly used in oil and gas field development include nanoscale SiO2, Al2O3, and molybdenum disulfide. However, their poor surface activity, tendency to agglomerate, and large size significantly limit their application in high-temperature, high-salinity, low-permeability reservoirs. To overcome these limitations of nanomaterials, the application of amphiphilic carbon dots has attracted attention. Amphiphilic carbon dots are small (1–10 nm) carbon nanomaterials that contain both hydrophilic and hydrophobic groups. Their high interfacial activity holds great promise for enhancing oil recovery. To further enhance the high-temperature and high-salinity resistance of existing oil displacement agents, the preparation of high-interfacial-activity amphiphilic carbon dots for high-temperature and high-salinity oil displacement has become an urgent challenge. Summary of the Invention

[0004] In view of the technical problems existing in the background technology, the present invention provides an amphiphilic carbon dot, carbon nanofluid and its application, aiming to solve the technical problems of poor surface activity and poor high temperature and high salt resistance of existing conventional nanomaterial oil displacement agents.

[0005] In a first aspect, the present invention provides an amphiphilic carbon dot, which is prepared by solvent thermal reaction of alkylphenol polyoxyethylene ether and glucose as raw materials; the alkylphenol polyoxyethylene ether includes octylphenol polyoxyethylene ether and / or nonylphenol polyoxyethylene ether; the mass ratio of alkylphenol polyoxyethylene ether to glucose is 1: (0.1~2).

[0006] Preferably, the octylphenol polyoxyethylene ether includes at least one of OP-7, OP-10, OP-15, and OP-20.

[0007] Preferably, the nonylphenol polyoxyethylene ether includes at least one of NP-10, NP-12 and NP-15.

[0008] Preferably, the solvent includes at least one of methanol, ethanol, n-propanol, water, dimethylformamide, acetone and dimethyl sulfoxide; the volume ratio of the total mass of alkylphenol polyoxyethylene ether and the glucose to the solvent is 1g: (20~70)mL.

[0009] Preferably, the reaction temperature of the solvothermal reaction is 160-200° C., and the reaction time is 6-12 h.

[0010] In a second aspect, the present invention provides a method for preparing the amphiphilic carbon dots as described in the first aspect, comprising the following steps:

[0011] Alkylphenol polyoxyethylene ether, glucose and solvent are mixed and then subjected to solvothermal reaction to obtain amphiphilic carbon dots.

[0012] In a third aspect, the present invention provides a carbon nanofluid, wherein the raw materials for preparing the carbon nanofluid include the amphiphilic carbon dots described in the first aspect.

[0013] Preferably, the raw materials for preparing the carbon nanofluid include, by weight percentage, 0.06% to 0.7% of amphiphilic carbon dots, 0.03% to 0.6% of zwitterionic surfactants, 10.5% to 21.5% of inorganic salts, and the balance water.

[0014] Preferably, the zwitterionic surfactant includes at least one of lauryl dimethyl hydroxypropyl sulfobetaine, octadecyl dimethyl betaine, oleamidopropyl hydroxysulfobetaine, cetearyl dimethyl hydroxypropyl sulfobetaine, lauryl amide propyl betaine, lauryl amide propyl hydroxysulfobetaine, oleamidopropyl betaine, octadecyl hydroxypropyl sulfobetaine, and cocamide hydroxypropyl sulfobetaine.

[0015] Preferably, the inorganic salts include sodium chloride and calcium chloride.

[0016] In a fourth aspect, the present invention provides a use of the carbon nanofluid as described in the third aspect in oil recovery from low permeability and high temperature reservoirs, and / or oil recovery from high salinity and low permeability deep reservoirs.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention provides amphiphilic carbon dots (Cdots) prepared from alkylphenol polyoxyethylene ethers (APEs) and glucose via a one-step solvent process. By varying the alkylbenzene chain length and the amount of APEs in the raw materials, and adjusting the mass ratio of APEs to glucose, the Cdots are then subjected to solvent thermal conditions to facilitate the preparation of Cdots with varying surface and interfacial activities. The Cdots remain stable and do not aggregate after aging for seven days at high temperature and high salinity, exhibiting excellent surface and interfacial activity. They exhibit high oil washing efficiency from oil sands and can improve crude oil recovery from high-temperature, high-salinity, low-permeability reservoirs.

[0019] The carbon nanofluid provided by the present invention is a compound of amphiphilic carbon dots and zwitterionic surfactants, which can further improve the stability of the carbon nanofluid oil displacement system under high temperature and high salinity conditions, and can adjust the sandstone surface from an oil-wet state to a water-wet state, thereby improving the oil sand washing efficiency. At the same time, it has excellent surface and interfacial properties, increases crude oil recovery, and realizes efficient production increase and development of high-temperature, high-salinity deep oil reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The figure is a bar graph showing the oil washing efficiency of the carbon nanofluid oil displacement agents prepared in Examples 1 to 12 of the present invention, the blank group, and Comparative Examples 1 to 8;

[0021] Figure 2 This is a curve showing the crude oil recovery rate and injection pressure of the carbon nanofluid oil displacement agent prepared in Example 3 of the present invention as a function of the injection volume. DETAILED DESCRIPTION

[0022] The following embodiments of the technical solution of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are therefore only examples and are not intended to limit the scope of protection of the present invention.

[0023] In order to solve the technical problems of low interfacial activity and poor high temperature and high salt resistance of conventional nanomaterials, the present invention provides an amphiphilic carbon dot, a carbon nanofluid and its application. The amphiphilic carbon dot is synthesized by solvent thermal method using alkylphenol polyoxyethylene ether and glucose as raw materials to obtain amphiphilic carbon dots with high surface and interfacial activity. The amphiphilic carbon dots can withstand high temperature (130°C) and high mineralization (2.1×10 5 After aging for 7 days at 400 mg / L, the product remained stable without precipitation and still exhibited good surface and interfacial activity.

[0024] In a first aspect, an embodiment of the present invention provides an amphiphilic carbon dot, which is prepared by a solvothermal reaction of alkylphenol polyoxyethylene ether and glucose as raw materials; the alkylphenol polyoxyethylene ether includes octylphenol polyoxyethylene ether (OPEO) and / or nonylphenol polyoxyethylene ether (NPEO); the mass ratio of the alkylphenol polyoxyethylene ether to the glucose is 1:(0.1~2).

[0025] In the technical solution of the present invention, alkylphenol polyoxyethylene ethers and glucose, respectively, contain numerous ether groups and hydroxyl groups, serving as the hydrophilic portion of the carbon core. Glucose, with its high carbon-to-hydrogen ratio, serves as the primary raw material for carbon dot formation. The terminal hydroxyl groups of the alkylphenol polyoxyethylene ethers can undergo an alkylation reaction with glucose, allowing the alkylbenzene chains in the alkylphenol polyoxyethylene ethers to serve as the hydrophobic carbon chains of the carbon core. The ether groups, hydroxyl groups, and alkylbenzene chains at the edges of the carbon core impart excellent surface and interfacial activity to the amphiphilic carbon dots. The alkylbenzene chains, in particular, share structural similarities with the saturated alkanes and aromatic hydrocarbons in crude oil, effectively reducing the interfacial tension between crude oil and water.

[0026] Further, in some embodiments, the alkylphenol polyoxyethylene ether includes octylphenol polyoxyethylene ether (OPEO) and / or nonylphenol polyoxyethylene ether (NPEO).

[0027] Furthermore, in some embodiments, the octylphenol polyoxyethylene ether includes at least one of OP-7, OP-10, OP-15, and OP-20.

[0028] Further, in some embodiments, the nonylphenol polyoxyethylene ether includes at least one of NP-10, NP-12, and NP-15.

[0029] In the technical solution of the embodiment of the present invention, by varying the alkyl chain length and the amount of polyoxyethylene ether in the raw materials, adjusting the mass ratio of alkylphenol polyoxyethylene ether to glucose, and performing carbon dotization under solvothermal conditions, amphiphilic carbon dots with different surface and interfacial activities are easily prepared. If the alkylphenol polyoxyethylene ether accounts for a large proportion, the hydrophobic chains of the amphiphilic carbon dots increase; if the alkylphenol polyoxyethylene ether accounts for a small proportion, the hydrophilic groups of the amphiphilic carbon dots increase.

[0030] Further, in some embodiments, the solvent includes at least one of methanol, ethanol, n-propanol, water, dimethylformamide (DMF), acetone, and dimethyl sulfoxide (DMSO).

[0031] Furthermore, in some embodiments, the volume ratio of the total mass of alkylphenol polyoxyethylene ether and glucose to the solvent is 1 g: (20-70) mL.

[0032] Furthermore, in some embodiments, the reaction temperature of the solvothermal reaction is 160-200° C., and the reaction time is 6-12 h.

[0033] In a second aspect, an embodiment of the present invention provides a method for preparing the amphiphilic carbon dots as described in the first aspect, comprising the following steps:

[0034] Alkylphenol polyoxyethylene ether, glucose and solvent are mixed and then subjected to solvothermal reaction to obtain amphiphilic carbon dots.

[0035] Furthermore, in some embodiments, a post-processing step is further included after the solvent thermal reaction is completed. The post-processing step specifically includes: after the reaction is completed, the reaction mixture is cooled, and then centrifuged and evaporated to remove the solvent to obtain a crude product, and the crude product is dissolved in water and dialyzed and freeze-dried to obtain amphiphilic carbon dots.

[0036] Furthermore, in some embodiments, a dialysis bag with a molecular weight cut-off of 500-2000 Da is used in dialysis.

[0037] In a third aspect, an embodiment of the present invention provides a carbon nanofluid, wherein the raw materials for preparing the carbon nanofluid include the amphiphilic carbon dots described in the first aspect.

[0038] Furthermore, in some embodiments, the raw materials for preparing the carbon nanofluid include, by weight percentage, 0.06% to 0.7% of amphiphilic carbon dots, 0.03% to 0.6% of zwitterionic surfactants, 10.5% to 21.5% of inorganic salts, and the balance water.

[0039] In the technical solutions of the embodiments of the present invention, zwitterionic surfactants exhibit electrical neutrality in aqueous solutions due to the presence of an equal number of anionic and cationic groups in their molecular structures, resulting in excellent salt tolerance. The present invention further enhances the system's resistance to high temperatures and high salinity by compounding the prepared amphiphilic carbon dots with zwitterionic surfactants. Simultaneously, an inorganic salt solution is added to the mixture to simulate the salinity of formation water, enhancing the stability of the carbon nanofluid flooding system under high-temperature, high-salinity conditions.

[0040] Furthermore, in some embodiments, the carbon nanofluid comprises, by weight percentage, 0.1% to 0.4% of amphiphilic carbon dots, 0.2% to 0.5% of zwitterionic surfactant, 15.5% to 21.2% of inorganic salt, and the balance water.

[0041] Further, in some embodiments, the zwitterionic surfactant includes at least one of lauryl dimethyl hydroxypropyl sulfobetaine (HSB1214), stearyl dimethyl betaine (BS-18), oleamidopropyl hydroxysulfobetaine (OHSB), cetearyl dimethyl hydroxypropyl sulfobetaine (HSB1618), lauramidopropyl betaine (LAB), lauramidopropyl hydroxysulfobetaine (LHSB), oleamidopropyl betaine (OAB), stearyl hydroxypropyl sulfobetaine (DHSB), and cocamide hydroxypropyl sulfobetaine (CHSB).

[0042] Further, in some embodiments, the inorganic salt includes sodium chloride and calcium chloride.

[0043] Furthermore, in some embodiments, the inorganic salt in the carbon nanofluid is 15% to 20% by mass of NaCl and 0.5% to 1.2% by mass of CaCl2.

[0044] In a fourth aspect, an embodiment of the present invention provides a use of the carbon nanofluid as described in the third aspect in oil recovery from low permeability, high-temperature reservoirs, and / or high-salinity, low-permeability deep reservoirs.

[0045] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this field or the product specifications were used. Where the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be purchased commercially.

[0046] 1. Preparation method

[0047] Example 1

[0048] An amphiphilic carbon dot, the preparation method thereof is as follows:

[0049] 0.75 g of nonylphenol polyoxyethylene ether NP-10 and 0.75 g of glucose were added to 50 mL of deionized water, stirred thoroughly and dissolved, and the above aqueous solution was charged into a high-temperature reactor and placed in an oven at 180°C for hydrothermal reaction for 12 hours. After the reaction, it was cooled to room temperature, and the reaction solution was taken out and centrifuged at a speed of 10,000 rpm. After filtration, the filtrate was taken into a reduced pressure rotary evaporator to remove the solvent to obtain a crude product. The crude product was dissolved in water and dialyzed and purified using a dialysis bag with a molecular weight cutoff of 500 Da for 48 hours. Finally, it was freeze-dried to obtain amphiphilic carbon dots.

[0050] A carbon nanofluid, the preparation method of which is as follows:

[0051] 0.5 g of the above-mentioned amphiphilic carbon dots, 20 g of NaCl and 1 g of CaCl2 were weighed and dissolved in deionized water, and the volume was adjusted to 100 mL to obtain a carbon nanofluid containing amphiphilic carbon dots.

[0052] Example 2

[0053] An amphiphilic carbon dot, the preparation method thereof is as follows:

[0054] 0.75 g of octylphenol polyoxyethylene ether OP-7 and 0.75 g of glucose were added to 50 mL of deionized water, stirred thoroughly and dissolved, and the above aqueous solution was charged into a high-temperature reactor and placed in an oven at 180°C for hydrothermal reaction for 12 hours. After the reaction, it was cooled to room temperature, and the reaction solution was taken out and centrifuged at a speed of 10,000 rpm. After filtration, the filtrate was taken into a vacuum rotary evaporator to remove the solvent to obtain a crude product. The crude product was dissolved in water and dialyzed and purified using a dialysis bag with a molecular weight cutoff of 500 Da for 48 hours. Finally, it was freeze-dried to obtain amphiphilic carbon dots.

[0055] A carbon nanofluid, the preparation method of which is as follows:

[0056] 0.5 g of the above-mentioned amphiphilic carbon dots, 20 g of NaCl and 1 g of CaCl2 were weighed and dissolved in deionized water, and the volume was adjusted to 100 mL to obtain a carbon nanofluid containing amphiphilic carbon dots.

[0057] Example 3

[0058] A carbon nanofluid, the preparation method of which is as follows:

[0059] 0.25 g of the amphiphilic carbon dots prepared in Example 1 was weighed, along with 0.25 g of DHSB (octadecylhydroxypropylsulfobetaine) amphoteric surfactant, 20 g of NaCl, and 1 g of CaCl2. These reagents were dissolved in deionized water and the volume was adjusted to 100 mL to obtain a carbon nanofluid containing amphiphilic carbon dots.

[0060] Example 4

[0061] 0.25 g of the amphiphilic carbon dots prepared in Example 2 was weighed, along with 0.25 g of DHSB (octadecylhydroxypropylsulfobetaine) amphoteric surfactant, 20 g of NaCl, and 1 g of CaCl2. These reagents were dissolved in deionized water and the volume was adjusted to 100 mL to obtain a carbon nanofluid containing amphiphilic carbon dots.

[0062] Example 5

[0063] 0.25 g of the amphiphilic carbon dots prepared in Example 1 was weighed, along with 0.25 g of OAB (oleamidopropyl betaine) amphoteric surfactant, 20 g of NaCl, and 1 g of CaCl2. These reagents were dissolved in deionized water and the volume was adjusted to 100 mL to obtain a carbon nanofluid containing amphiphilic carbon dots.

[0064] Example 6

[0065] 0.25 g of the amphiphilic carbon dots prepared in Example 2 was weighed, along with 0.25 g of OAB (oleamidopropyl betaine) amphoteric surfactant, 20 g of NaCl, and 1 g of CaCl2. These reagents were dissolved in deionized water and the volume was adjusted to 100 mL to obtain a carbon nanofluid containing amphiphilic carbon dots.

[0066] Example 7

[0067] 0.25 g of the amphiphilic carbon dots prepared in Example 1 was weighed, along with 0.25 g of OHSB (oleamidopropyl hydroxysulfobetaine) amphoteric surfactant, 20 g of NaCl, and 1 g of CaCl2. These reagents were dissolved in deionized water and the volume was adjusted to 100 mL to obtain a carbon nanofluid containing amphiphilic carbon dots.

[0068] Example 8

[0069] 0.25 g of the amphiphilic carbon dots prepared in Example 2 was weighed, along with 0.25 g of OHSB (oleamidopropyl hydroxysulfobetaine) amphoteric surfactant, 20 g of NaCl, and 1 g of CaCl2. These reagents were dissolved in deionized water and the volume was adjusted to 100 mL to obtain a carbon nanofluid containing amphiphilic carbon dots.

[0070] Example 9

[0071] 0.25 g of the amphiphilic carbon dots prepared in Example 1 was weighed, along with 0.25 g of LAB (lauramidopropyl betaine) amphoteric surfactant, 20 g of NaCl, and 1 g of CaCl2. These reagents were dissolved in deionized water and the volume was adjusted to 100 mL to obtain a carbon nanofluid containing amphiphilic carbon dots.

[0072] Example 10

[0073] 0.25 g of the amphiphilic carbon dots prepared in Example 2 was weighed, along with 0.25 g of LAB (lauramidopropyl betaine) amphoteric surfactant, 20 g of NaCl, and 1 g of CaCl2. These reagents were dissolved in deionized water and the volume was adjusted to 100 mL to obtain a carbon nanofluid containing amphiphilic carbon dots.

[0074] Example 11

[0075] An amphiphilic carbon dot, the preparation method thereof is as follows:

[0076] 1.25 g of nonylphenol polyoxyethylene ether NP-10 and 0.25 g of glucose were added to 50 mL of deionized water, stirred thoroughly and dissolved, and the above aqueous solution was charged into a high-temperature reactor and placed in an oven at 180°C for hydrothermal reaction for 12 hours. After the reaction, it was cooled to room temperature, and the reaction solution was taken out and centrifuged at a speed of 10,000 rpm. After filtration, the filtrate was taken into a vacuum rotary evaporator to remove the solvent to obtain a crude product. The crude product was dissolved in water and dialyzed and purified using a dialysis bag with a molecular weight cutoff of 500 Da for 48 hours. Finally, it was freeze-dried to obtain amphiphilic carbon dots.

[0077] A carbon nanofluid, the preparation method of which is as follows:

[0078] 0.5 g of the above-mentioned amphiphilic carbon dots, 20 g of NaCl and 1 g of CaCl2 were weighed and dissolved in deionized water, and the volume was adjusted to 100 mL to obtain a carbon nanofluid containing amphiphilic carbon dots.

[0079] Example 12

[0080] An amphiphilic carbon dot, the preparation method thereof is as follows:

[0081] 0.5 g of nonylphenol polyoxyethylene ether NP-10 and 1 g of glucose were added to 50 mL of deionized water, stirred thoroughly and dissolved, and the above aqueous solution was charged into a high-temperature reactor and placed in an oven at 180°C for hydrothermal reaction for 12 hours. After the reaction, it was cooled to room temperature, and the reaction solution was taken out and centrifuged at a speed of 10,000 rpm. After filtration, the filtrate was taken into a vacuum rotary evaporator to remove the solvent to obtain a crude product. The crude product was dissolved in water and dialyzed and purified using a dialysis bag with a molecular weight cutoff of 500 Da for 48 hours. Finally, it was freeze-dried to obtain amphiphilic carbon dots.

[0082] A carbon nanofluid, the preparation method of which is as follows:

[0083] 0.5 g of the above-mentioned amphiphilic carbon dots, 20 g of NaCl and 1 g of CaCl2 were weighed and dissolved in deionized water, and the volume was adjusted to 100 mL to obtain a carbon nanofluid containing amphiphilic carbon dots.

[0084] Blank group

[0085] Weigh 20 g of NaCl and 1 g of CaCl2, dissolve the above reagents in deionized water, and dilute to 100 mL to obtain the displacement fluid for the blank group experiment.

[0086] Comparative Example 1

[0087] Weigh 0.5 g of DHSB amphoteric surfactant, 20 g of NaCl, and 1 g of CaCl2, dissolve the above reagents in deionized water, and dilute to 100 mL to obtain an oil-displacing agent.

[0088] Comparative Example 2

[0089] Weigh 0.5 g of OAB amphoteric surfactant, 20 g of NaCl and 1 g of CaCl2, dissolve the above reagents in deionized water, and dilute to 100 mL to obtain an oil-displacing agent.

[0090] Comparative Example 3

[0091] Weigh 0.5 g of OHSB amphoteric surfactant, 20 g of NaCl and 1 g of CaCl2, dissolve the above reagents in deionized water, and dilute to 100 mL to obtain an oil-displacing agent.

[0092] Comparative Example 4

[0093] Weigh 0.5 g of LAB amphoteric surfactant, 20 g of NaCl, and 1 g of CaCl2, dissolve the above reagents in deionized water, and dilute to 100 mL to obtain an oil-displacing agent.

[0094] Comparative Example 5

[0095] Only 1.5 g of nonylphenol polyoxyethylene ether NP-10 was added to 50 mL of deionized water, fully stirred and dissolved, and a hydrothermal reaction was performed. Other reaction conditions and experimental steps were the same as in Example 1 to obtain amphiphilic carbon dots.

[0096] 0.5 g of the above-mentioned amphiphilic carbon dots, 20 g of NaCl and 1 g of CaCl2 were weighed and dissolved in deionized water and the volume was adjusted to 100 mL to obtain carbon nanofluid.

[0097] Comparative Example 6

[0098] Only 1.5 g of glucose was added to 50 mL of deionized water, stirred and dissolved, and subjected to a hydrothermal reaction. Other reaction conditions and experimental steps were the same as those in Example 1 to obtain hydrophilic carbon dots.

[0099] 0.5 g of the hydrophilic carbon dots, 20 g of NaCl, and 1 g of CaCl2 were weighed and dissolved in deionized water and the volume was adjusted to 100 mL to obtain a carbon nanofluid.

[0100] Comparative Example 7

[0101] Only 1.5 g of glucose was added to 50 mL of deionized water, stirred and dissolved, and subjected to a hydrothermal reaction. Other reaction conditions and experimental steps were the same as those in Example 1 to obtain hydrophilic carbon dots.

[0102] 0.25 g of the above-mentioned hydrophilic carbon dots, 0.25 g of nonylphenol polyoxyethylene ether NP-10, 20 g of NaCl and 1 g of CaCl2 were weighed and dissolved in deionized water, and the volume was adjusted to 100 mL to obtain a carbon nanofluid.

[0103] Comparative Example 8

[0104] The amphiphilic carbon dots in this comparative example are the carbon dot material C synthesized in Example 3 of the previous public application document CN117070203A of the present applicant. 1214 -ACDs.

[0105] Weigh 0.5g of amphiphilic nanocarbon dots C 1214 -ACDs, 20 g NaCl and 1 g CaCl2 were dissolved in deionized water and the volume was adjusted to 100 mL to obtain carbon nanofluid.

[0106] 2. Test Method

[0107] 1. Oil-water interfacial tension and contact angle test before and after aging of oil displacement agent

[0108] The carbon nanofluid flooding systems obtained in Examples 1 to 12 of the present invention, the blank group, and Comparative Examples 1 to 8 were subjected to high-temperature aging experiments, oil-water interfacial tension, and contact angle tests. The specific steps are as follows:

[0109] 50 mL of the carbon nanofluid flooding system obtained in Examples 1 to 12, the blank group, and Comparative Examples 1 to 8 of the present invention was placed in a high-temperature reactor for aging test. The system was placed in a 130°C oven for 7 days, then removed from the reactor and cooled to room temperature for later use.

[0110] The oil-water interfacial tension values ​​of each system before and after high-temperature aging and its wetting control performance on hydrophobically modified glass sheets (contact angle test) were evaluated. The oil-water interfacial tension was measured as follows: the oil-water interfacial tension of the oil displacement agent before and after aging was measured using a spinning drop interfacial tension meter at a test temperature of 60°C. The density of the crude oil at 60°C was 0.8765 g / cm 3 The contact angle was measured as follows: a clean hydrophilic glass slide was soaked in dimethyl silicone oil for hydrophobic modification to obtain an oleophilic glass slide. The oleophilic glass slide had a water droplet contact angle of 104±5°. The oleophilic glass slide was suspended in different carbon nanofluid oil displacement agents for 24 hours. The slide was removed and dried, and the contact angle of the water droplet on the glass slide was measured.

[0111] 2. Oil sand cleaning experiment

[0112] The oil-displacing agents prepared in Examples 1 to 12, the blank group, and Comparative Examples 1 to 8 were subjected to an oil sand cleaning experiment to further evaluate the oil-washing efficiency of each oil-displacing system. The method is as follows:

[0113] Oil sands were prepared by thoroughly mixing crude oil with 120-mesh quartz sand in a 1:4 ratio and aging in a 130°C oven for 24 hours. The aged oil sands were then mixed with each displacement system in a 1:3 mass ratio on a shaker at 60-200 rpm. The sands were then cleaned at 130°C for 48 hours. The oil-containing wash solution and the supernatant crude oil were removed, and the remaining oil sands were collected, dried, and weighed. The difference in mass before and after washing was calculated to determine the oil displacement agent's cleaning efficiency.

[0114] 3. Core flooding experiment

[0115] The carbon nanofluid flooding systems obtained in Examples 1 to 12 and Comparative Examples 1 to 8 were subjected to core flooding experiments to further evaluate the enhanced crude oil recovery performance of the carbon nanofluids. The specific method is as follows:

[0116] An artificial sandstone core 7 cm long and 2.5 cm in diameter was selected and dried in a 120°C oven for 4 hours. The core was cooled to room temperature and weighed to obtain the dry weight. The core was then evacuated and saturated with simulated brine (a mixture of 20% NaCl and 1% CaCl₂ in water) in a vacuum extraction device. The core was removed, the surface of the simulated brine wiped clean, and the weight loss was measured to calculate the core porosity. The core permeability was measured using this simulated brine according to the petroleum and natural gas industry standard SY / T5336-2006, "Core Analysis Methods." The core was dried again and saturated with crude oil in an extraction device. A core displacement experiment was conducted in a core holder at 130°C: first, water flooding was performed using the simulated brine described above, with an injection volume of 1.5 PV and a pump flow rate of 0.1 mL / min until no more oil was produced in the graduated cylinder. The oil volume produced was recorded and the water flooding recovery factor was calculated. Then, oil was displaced using the prepared carbon nanofluid at a flow rate of 0.1 mL / min. The injection volume of all carbon nanofluids or surfactant oil-displacing agents was 1 PV. The pump was stopped, and the oil volume produced was recorded and the enhanced crude oil recovery factor was calculated. The displacement working fluid was the oil-displacing agent of the carbon nanofluid oil-displacing system obtained in Examples 1 to 12 and Comparative Examples 1 to 8 after aging at 130°C for 7 days.

[0117] 3. Analysis of test results of various embodiments and comparative examples

[0118] 1. Test results of oil-water interfacial tension and contact angle before and after aging of oil displacement agent

[0119] The oil-water interfacial tension values ​​and contact angle data of Examples 1 to 12, the blank group, and Comparative Examples 1 to 8 are shown in Table 1.

[0120] Table 1 Oil-water interfacial tension and contact angle data

[0121]

[0122] As shown in Table 1, for Examples 1 to 12, after the carbon nanofluid oil-displacing agent was treated with the hydrophobic glass sheet, the wettability of the hydrophobic glass sheet was adjusted to hydrophilic (the contact angles were all less than 50°); after high-temperature aging, the wettability of the carbon nanofluid oil-displacing agent of Examples 3 to 10 remained almost unchanged, indicating that the carbon nanofluid oil-displacing agent has excellent temperature resistance and is 5 The oil-displacing agents described in Comparative Examples 1 to 8 all exhibited lower wettability and control performance on hydrophobic glass sheets than those in Examples 1 to 12.

[0123] At the same time, the oil-water interfacial tension of the carbon nanofluid oil displacement agents of Examples 1 to 12 in Table 1 did not change much before and after high-temperature aging. The oil-water interfacial tension values ​​of Examples 3 to 10 remained at 10 -3 Ultra-low interfacial tension of the order of mN / m. However, the interfacial tension values ​​of the oil-displacing agents prepared in Comparative Examples 1 to 4 increased significantly before and after high-temperature aging. The contact angle and oil-water interfacial tension of the carbon nanofluid oil-displacing agent in Comparative Example 5 are both higher than those in Example 1, and its interfacial activity is lower than that in Example 1, indicating that alkylphenol polyoxyethylene ether and glucose need to be used together as the synthetic raw materials of amphiphilic carbon dots to effectively regulate their hydrophilic and lipophilic properties and increase their surface and interfacial activity; however, there is little difference before and after high-temperature aging, and the amphiphilic carbon nanofluid has excellent high-temperature resistance. In Comparative Example 6, only glucose is used as the synthetic raw material for carbon dots, and no hydrophobic carbon dots are introduced. It is a hydrophilic carbon dot with certain wettability regulation properties, but it does not have amphiphilicity, poor interfacial activity, and its interfacial tension value is similar to that of the blank group. Comparative Example 7 has certain wettability control and surface activity, but its performance is significantly reduced after high-temperature aging. This is due to the low cloud point of the alkylphenol polyoxyethylene ether surfactant. This shows that the amphiphilic carbon dot nanomaterial synthesized after solvent thermal treatment of alkylphenol polyoxyethylene ether has higher temperature and salt resistance than when it is directly added to the carbon nanofluid as a surfactant.

[0124] The contact angle and oil-water interfacial tension values ​​of Comparative Example 8 are both higher than those of Examples 1 and 2, indicating that the microscopic molecular structure of the amphiphilic carbon dots determines the level of their interfacial activity. The hydrophobic portion of the amphiphilic carbon dots prepared in Comparative Example 8 is an alkyl chain, while the hydrophobic portion of the amphiphilic carbon dots synthesized in the present invention is composed of alkyl and phenyl groups, and its structure is more similar to the saturated alkanes and aromatic hydrocarbon components in crude oil. Compared with Comparative Example 8, it is easier to adsorb at the oil / solid and oil / water interfaces, thereby improving the interfacial activity.

[0125] 2. Oil sand cleaning test results

[0126] Figure 1 The oil washing efficiency bar graph of the carbon nanofluid oil displacement agent prepared in Examples 1 to 12, the blank group and the comparative examples 1 to 8 is shown. Figure 1 Compared to the blank control and Comparative Examples 1-8, the oil-washing efficiency of the carbon nanofluids in Examples 1-2 exceeded 80%. The oil-washing efficiency of Examples 1 and 2 was higher than that of Comparative Example 8 (75.34%), indicating that carbon dot structures containing both alkyl and phenyl hydrophobic chains possess superior oil-washing performance. Furthermore, the oil-washing performance of the carbon nanofluids in Examples 3-10 was significantly improved compared to that of Examples 1 and 2, reaching 90%, indicating that the amphiphilic carbon dots and zwitterionic surfactants exhibit excellent synergistic performance.

[0127] 3. Core flooding test results

[0128] The relevant core physical property parameters and crude oil recovery experimental data of each group are shown in Table 2.

[0129] Table 2 Core physical properties and enhanced oil recovery data

[0130]

[0131] As shown in Table 2, the permeability of the core used in the displacement experiment is 10×10 -3 μm 2 The water flooding permeabilities of the cores used in Examples 1-12 and Comparative Examples 1-8 were similar, ranging from 30% to 40%. Examples 1-12 significantly improved oil recovery. Specifically, Examples 3, 6, and 7 increased oil recovery by over 24% at 130°C and high salinity (aqueous solution of 20% NaCl and 1% CaCl₂), representing significant increases compared to Comparative Examples 1-8. Comparing the oil flooding performance of Comparative Example 8 with that of Examples 1 or 2 demonstrates the performance advantages of the hydrophobic structure of the alkylbenzene chain in improving oil recovery.

[0132] Figure 2 The curves of the enhanced oil recovery and injection pressure of the carbon nanofluid oil displacement agent obtained in Example 3 as the displacement medium and its volume change. Figure 2 It can be seen that Example 3 can significantly reduce the injection pressure from 1.12 MPa to 0.71 MPa, and the oil recovery rate can be increased by 25.86% after water flooding.

[0133] It should be noted that the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the technical solution of the present invention are all included in the technical scope of the present invention. In addition, without departing from the scope of the present invention, other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present invention.

Claims

1. An amphiphilic carbon dot, characterized in that: The amphiphilic carbon dots are prepared by solvent thermal reaction using alkylphenol polyoxyethylene ether and glucose as raw materials; the alkylphenol polyoxyethylene ether includes octylphenol polyoxyethylene ether and / or nonylphenol polyoxyethylene ether; the mass ratio of the alkylphenol polyoxyethylene ether to the glucose is 1:(0.1~2).

2. The amphiphilic carbon dot according to claim 1, characterized in that The octylphenol polyoxyethylene ether includes at least one of OP-7, OP-10, OP-15, and OP-20; and / or the nonylphenol polyoxyethylene ether includes at least one of NP-10, NP-12, and NP-15.

3. The amphiphilic carbon dot according to claim 1, characterized in that The solvent includes at least one of methanol, ethanol, n-propanol, water, dimethylformamide, acetone and dimethyl sulfoxide; the volume ratio of the total mass of the alkylphenol polyoxyethylene ether and the glucose to the solvent is 1g: (20-70)mL.

4. The amphiphilic carbon dot according to claim 1, characterized in that The reaction temperature of the solvent thermal reaction is 160-200° C., and the reaction time is 6-12 hours.

5. The method for preparing amphiphilic carbon dots according to any one of claims 1 to 4, wherein: The steps include: Alkylphenol polyoxyethylene ether, glucose and a solvent are mixed evenly, and then subjected to a solvothermal reaction to obtain the amphiphilic carbon dots.

6. A carbon nanofluid, characterized in that: The raw materials for preparing the carbon nanofluid include the amphiphilic carbon dots as described in any one of claims 1 to 4.

7. The carbon nanofluid according to claim 6, characterized in that: The raw materials for preparing the carbon nanofluid include, by weight percentage, 0.06% to 0.7% of amphiphilic carbon dots, 0.03% to 0.6% of zwitterionic surfactants, 10.5% to 21.5% of inorganic salts, and the balance of water.

8. The carbon nanofluid according to claim 7, characterized in that: The zwitterionic surfactant includes at least one of lauryl dimethyl hydroxypropyl sulfobetaine, octadecyl dimethyl betaine, oleamidopropyl hydroxysulfobetaine, cetearyl dimethyl hydroxypropyl sulfobetaine, lauryl amide propyl betaine, lauryl amide propyl hydroxysulfobetaine, oleamidopropyl betaine, octadecyl hydroxypropyl sulfobetaine, and cocamide hydroxypropyl sulfobetaine.

9. The carbon nanofluid according to claim 7, characterized in that: The inorganic salts include sodium chloride and calcium chloride.

10. Use of the carbon nanofluid according to any one of claims 6 to 9 in oil displacement from low permeability and high temperature reservoirs, and / or oil displacement from high salinity and low permeability deep reservoirs.

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