An amphiphilic carbon dot-based pressure-driven integration working fluid, a preparation method and application thereof

Abstract

The application provides a pressure fracturing and oil displacement integrated working fluid based on amphiphilic carbon dots, a preparation method and application thereof, and belongs to the field of oil field chemistry, wherein the preparation method comprises the following steps: dissolving a first non-ionic monomer, a first salt-tolerant anionic monomer, a long carbon chain cationic monomer, a crosslinking agent and a first initiator in water, performing hydrothermal reaction at 160-200 DEG C, and cooling to obtain an amphiphilic carbon dot mother liquor; adding a second non-ionic monomer, a second salt-tolerant anionic monomer, an inorganic salt and a second initiator into the amphiphilic carbon dot mother liquor, and performing polymerization reaction to obtain the pressure fracturing and oil displacement integrated working fluid. The application synthesizes amphiphilic carbon dots as oil displacement functional units and nano stabilizers, and then uses the same as a dispersion medium to obtain a composite working fluid containing a high molecular resistance reducing agent through water dispersion polymerization reaction; the high molecular in the working fluid provides fracturing resistance reduction performance, the amphiphilic carbon dots provide interfacial activity and wetting modification performance, and the two are integrated to realize the functions of fracturing resistance reduction and oil displacement enhanced oil recovery.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to an integrated pressure-driven working fluid based on amphiphilic carbon points, its preparation method, and its application. Background Technology

[0002] Hydraulic fracturing technology is a core method for increasing reserves and production in low-permeability, tight oil and gas, and shale oil and gas fields. As the "lifeblood" of hydraulic fracturing, fracturing fluid not only transmits surface pump pressure and splits the formation to create fractures, but also carries proppant (such as ceramsite and silica sand) deep into the fractures to maintain their conductivity. With oil and gas exploration expanding into deeper and unconventional areas, reservoir environments are becoming increasingly complex (high temperature, high salinity, low porosity, and low permeability), placing higher demands on the performance of fracturing fluids. Looking at the history of fracturing technology, traditional fracturing fluid systems have mainly evolved from oil-based to water-based, and from high-viscosity fracture creation to low-viscosity volumetric fracturing. Based on the different dispersion media and thickening mechanisms, the traditional fracturing fluids widely used in industry can be mainly divided into four categories: water-based fracturing fluids (including slickwater and gum guar gum), oil-based fracturing fluids, foam / energy-enhancing fracturing fluids, and acid-based fracturing fluids.

[0003] The aforementioned traditional fracturing fluids have supported the development of the oil and gas industry over the past few decades, but their limitations are becoming increasingly apparent when facing the development of tight oil / shale oil with nanoscale pore throats: (1) Lack of "oil displacement" function: Traditional fracturing fluids (especially slickwater) only focus on "fracture creation" and "drag reduction", lacking the ability to change the wettability of rocks. In the well-clogging stage after fracturing, it is impossible to use capillary force to spontaneously absorb into the matrix micropores to replace crude oil, resulting in "fractures being created, but oil not coming out". (2) Insufficiently low interfacial tension: The oil-water interfacial tension of traditional systems is usually between 1 and 30 mN / m, making it difficult to activate the bound oil in the micropore throats. (3) High adsorption loss: Traditional chemical surfactants are severely adsorbed on the surface of underground rocks, with a short effective action distance, and are prone to failure under high temperature and high salinity. In summary, traditional fracturing fluid systems can hardly meet the high-efficiency development requirements of unconventional oil and gas "fracture-oil displacement integration". Developing functional nanofluids (such as amphiphilic carbon dot working fluids) that possess both the low friction and low cost characteristics of slickwater and ultra-low interfacial tension and intelligent wetting reversal function has become a key technological direction that urgently needs to be broken through in the field of oilfield chemistry.

[0004] Existing pressure-driven hydraulic fluids are mainly constructed by adding additives with percolation and displacement functions to slickwater. They primarily rely on surfactant systems or nanoemulsion systems. However, surfactant systems suffer severe adsorption loss on the surface of formation rocks (chromatographic separation effect), resulting in insufficient effective concentrations in deep fractures. While nanoemulsion systems are highly efficient, their high cost limits their large-scale application. Although nanoparticle (such as modified silica) oil displacement technology has emerged in recent years, its complex surface modification process and agglomeration stability issues in high-salt reservoir environments still restrict its widespread adoption. Therefore, developing a novel working fluid that is simple to prepare, has good stability, and combines molecular-level amphiphilicity with nanoscale size effects is currently an urgent need. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present invention provides an integrated hydraulic fracturing working fluid based on amphiphilic carbon points, its preparation method and application, aiming to solve the technical problems of traditional fracturing fluids having single function and lack of oil displacement capacity, as well as the high adsorption loss and high cost of existing integrated hydraulic fracturing working fluids.

[0006] In a first aspect, the present invention provides a method for preparing a pressure-driven integrated working fluid based on amphiphilic carbon dots, comprising the following steps: The first nonionic monomer, the first salt-tolerant anionic monomer, the long carbon chain cationic monomer, the crosslinking agent and the first initiator are dissolved in water and subjected to a hydrothermal reaction at 160~200℃. After cooling, an amphiphilic carbon dot mother liquor is obtained. A second nonionic monomer, a second salt-resistant anionic monomer, an inorganic salt, and a second initiator are added to the amphiphilic carbon dot mother liquor to carry out a polymerization reaction, thereby obtaining a pressure-driven integrated working fluid.

[0007] Preferably, the first nonionic monomer includes acrylamide and / or methacrylamide; The first salt-tolerant anionic monomer includes at least one of allyl sulfonic acid, methyl allyl sulfonic acid, vinyl sulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid; Long-chain cationic monomers include at least one of methacryloyloxydimethyloctylammonium chloride, methacryloyloxydimethyldodecylammonium chloride, and methacryloyloxydimethylhexadecylammonium chloride; Crosslinking agents include at least one of N,N'-methylenebisacrylamide, ethyl methacrylate, and polyethylene glycol diacrylate; The first initiator includes at least one of potassium persulfate, benzoyl peroxide, azobisisobutyronitrile, and azodialkylamidine; The ratio of the first nonionic monomer to water is (1~5) g: 100 mL; The first salt-tolerant anionic monomer to water ratio is (0.05~0.2) g: 100 mL; The feed-to-liquid ratio of long-chain cationic monomer to water is (0.05~0.2) g: 100 mL; The ratio of crosslinking agent to water is (0.05~0.2) g: 100 mL; The ratio of the first initiator to water is (0.05~0.2) g: 100 mL.

[0008] Preferably, the hydrothermal reaction time is 12-24 hours.

[0009] Preferably, the second nonionic monomer includes acrylamide and / or methacrylamide; The second salt-tolerant anionic monomer includes at least one of allyl sulfonic acid, methyl allyl sulfonic acid, vinyl sulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid; Inorganic salts include at least one of sodium chloride, ammonium chloride, sodium sulfate, and ammonium sulfate; The second nonionic monomer accounts for 15% to 30% of the mass of the amphiphilic carbon dot mother liquor; The mass of the second salt-tolerant anionic monomer accounts for 1% to 3% of the mass of the amphiphilic carbon dot mother liquor; The mass of inorganic salts accounts for 10% to 20% of the mass of the amphiphilic carbon dot mother liquor.

[0010] Preferably, the second initiator is an azo initiator or a redox initiator; the amount of the second initiator added is 0.001% to 0.1% of the total mass of the second nonionic monomer and the second salt-resistant anionic monomer.

[0011] Preferably, the azo initiator includes 2,2'-azobisisobutylamidine dihydrochloride or 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride.

[0012] Preferably, the redox initiator is composed of an oxidant and a reducing agent; the oxidant includes any one of ammonium persulfate, sodium persulfate, and potassium persulfate; the reducing agent includes any one of sodium bisulfite and sodium sulfite; the mass ratio of the oxidant to the reducing agent is (1~1.5):2.

[0013] Preferably, when the second initiator is an azo initiator, the polymerization temperature is 40~60℃; when the second initiator is a redox initiator, the polymerization temperature is 0~30℃.

[0014] Secondly, the present invention provides a pressure-driven integrated working fluid based on amphiphilic carbon dots, which is prepared by the preparation method described in the first aspect.

[0015] Thirdly, the present invention provides an application of an integrated pressure-driven working fluid based on amphiphilic carbon points in crude oil recovery.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention prepares amphiphilic carbon dots from low-cost monomers, and uses the amphiphilic carbon dots as stabilizers to prepare a pressure-driven integrated system with high drag reduction performance by water dispersion polymerization. This system also has ultra-low interfacial tension, wetting reversal performance and nano-effect.

[0017] In the pressure-driven integrated working fluid system based on amphiphilic carbon dots provided by this invention, the amphiphilic carbon dots can spontaneously adsorb onto the surface of oil-wetted rocks, changing the wettability from strong oil-wetting to strong water-wetting. Its contact angle alteration ability is significantly superior to that of traditional surfactants. Through the interaction between the lipophilic segments on the carbon dot surface and crude oil molecules, the oil-water interfacial tension is reduced to 10. -2 The carbon particles are on the order of mN / m. With a particle size of less than 10 nm, they can penetrate into micropores that traditional chemical agents cannot reach, displacing the retained crude oil. Attached Figure Description

[0018] Figure 1 This is a transmission electron microscope (TEM) image of the amphiphilic carbon dots in Example 1 of the present invention; Figure 2 These are photographs of the contact angle of the glass slide surface before and after treatment with the working fluid in Embodiment 1 of the present invention. Detailed Implementation

[0019] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0020] To address the technical problems of traditional fracturing fluids having limited functionality and lacking oil displacement capabilities, as well as the high adsorption losses and costs of existing integrated fracturing and hydraulic displacement working fluids, this invention provides an integrated fracturing and hydraulic displacement working fluid based on amphiphilic carbon dots, its preparation method, and its application. Specifically, amphiphilic carbon dots are synthesized as oil displacement functional units and nano-stabilizers, and then used as a dispersion medium for aqueous dispersion polymerization to obtain a composite working fluid containing a polymeric drag-reducing agent. The polymer in the working fluid provides fracturing drag reduction performance, while the amphiphilic carbon dots provide interfacial activity and wetting modification properties. The two work synergistically to achieve integrated fracturing drag reduction and oil displacement for enhanced oil recovery.

[0021] In a first aspect, embodiments of the present invention provide a method for preparing a pressure-driven integrated working fluid based on amphiphilic carbon dots, comprising the following steps: The first nonionic monomer, the first salt-tolerant anionic monomer, the long carbon chain cationic monomer, the crosslinking agent and the first initiator are dissolved in water and subjected to a hydrothermal reaction at 160~200℃. After cooling, an amphiphilic carbon dot mother liquor is obtained. A second nonionic monomer, a second salt-resistant anionic monomer, an inorganic salt, and a second initiator are added to the amphiphilic carbon dot mother liquor to carry out a polymerization reaction, thereby obtaining a pressure-driven integrated working fluid.

[0022] In the technical solution of this invention embodiment, an amphiphilic carbon dot-polymer composite hydraulic fracturing integrated working fluid is constructed through a two-step reaction. First, nonionic, anionic, and long-chain cationic monomers are used as raw materials, and reacted at high temperature under the action of a crosslinking agent and an initiator to obtain an amphiphilic carbon dot mother liquor. This carbon dot possesses both hydrophilic and oleophilic structures, which can reduce oil-water interfacial tension, alter rock wettability, and also provide nano-dispersion stabilization. Subsequently, using the amphiphilic carbon dot mother liquor as a dispersion medium, and the carbon dots simultaneously acting as a dispersion stabilizer, nonionic, anionic monomers, and inorganic salts are added, and water dispersion polymerization is initiated by an initiator to form a polymeric drag-reducing agent. In the resulting system, the polymer provides highly efficient drag reduction performance to meet the requirements of fracturing operations, while the amphiphilic carbon dots endow the system with oil displacement function. The two work synergistically to achieve integrated fracturing drag reduction and enhanced oil recovery.

[0023] Furthermore, in some embodiments, the first nonionic monomer includes acrylamide and / or methacrylamide; the feed-to-liquid ratio of the first nonionic monomer to water is (1~5) g: 100 mL.

[0024] Furthermore, in some embodiments, the first salt-resistant anionic monomer includes at least one of allyl sulfonic acid, methyl allyl sulfonic acid, vinyl sulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid; the feed-to-liquid ratio of the first salt-resistant anionic monomer to water is (0.05~0.2) g: 100 mL.

[0025] Furthermore, in some embodiments, the long-chain cationic monomer includes at least one of methacryloyloxydimethyloctylammonium chloride, methacryloyloxydimethyldodecylammonium chloride, and methacryloyloxydimethylhexadecylammonium chloride; the feed-to-liquid ratio of the long-chain cationic monomer to water is (0.05~0.2) g: 100 mL.

[0026] Furthermore, in some embodiments, the crosslinking agent includes at least one of N,N'-methylenebisacrylamide, ethyl methacrylate, and polyethylene glycol diacrylate; the ratio of crosslinking agent to water is (0.05~0.2) g: 100 mL.

[0027] Furthermore, in some embodiments, the first initiator includes at least one of potassium persulfate, benzoyl peroxide, azobisisobutyronitrile, and azodialkylamidine; the ratio of the first initiator to water is (0.05~0.2) g: 100 mL.

[0028] Furthermore, in some embodiments, the hydrothermal reaction time is 12-24 hours.

[0029] Furthermore, in some embodiments, the second nonionic monomer includes acrylamide and / or methacrylamide; the mass of the second nonionic monomer accounts for 15% to 30% of the mass of the amphiphilic carbon dot mother liquor.

[0030] Furthermore, in some embodiments, the second salt-resistant anionic monomer includes at least one of allyl sulfonic acid, methyl allyl sulfonic acid, vinyl sulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid; the mass of the second salt-resistant anionic monomer accounts for 1% to 3% of the mass of the amphiphilic carbon dot mother liquor.

[0031] Furthermore, in some embodiments, the inorganic salt includes at least one of sodium chloride, ammonium chloride, sodium sulfate, and ammonium sulfate; the inorganic salt accounts for 10% to 20% of the mass of the amphiphilic carbon point mother liquor.

[0032] Furthermore, in some embodiments, the second initiator is an azo initiator or a redox initiator; the amount of the second initiator added is 0.001% to 0.1% of the total mass of the second nonionic monomer and the second salt-resistant anionic monomer.

[0033] Furthermore, in some embodiments, the azo initiator includes 2,2'-azobisisobutylamidine dihydrochloride or 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride.

[0034] Furthermore, in some embodiments, the redox initiator is composed of an oxidant and a reducing agent; the oxidant includes any one of ammonium persulfate, sodium persulfate, and potassium persulfate; the reducing agent includes any one of sodium bisulfite and sodium sulfite; the mass ratio of the oxidant to the reducing agent is (1~1.5):2.

[0035] Furthermore, in some embodiments, when the second initiator is an azo initiator, the polymerization temperature is 40~60°C; when the second initiator is a redox initiator, the polymerization temperature is 0~30°C.

[0036] Secondly, embodiments of the present invention provide a pressure-driven integrated working fluid based on amphiphilic carbon dots, which is prepared by the preparation method described in the first aspect.

[0037] Thirdly, embodiments of the present invention provide an application of an integrated pressure-driven working fluid based on amphiphilic carbon points in crude oil recovery.

[0038] In this invention, the pressure-driven integrated working fluid based on amphiphilic carbon points achieves integrated pressure-driven operation. During the construction phase, it circulates as a low-resistance fracturing fluid, and during the well-clogging phase, it acts as a high-efficiency oil displacement agent that undergoes spontaneous permeation.

[0039] The following are some specific embodiments. It should be noted that the embodiments 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 embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0040] Example 1 A method for preparing a pressure-driven integrated working fluid based on amphiphilic carbon dots, the specific steps of which are as follows: (1) Weigh 3 g of acrylamide, 0.15 g of 2-acrylamido-2-methylpropanesulfonic acid, 0.1 g of methacryloyloxydimethyldodecylammonium chloride, 0.12 g of N,N'-methylenebisacrylamide and 0.1 g of potassium persulfate respectively, dissolve them in 100 mL of deionized water, place them in a reaction vessel and react at 180 °C for 12 hours, then cool to obtain amphiphilic carbon dot mother liquor; (2) Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and sodium chloride (accounting for 25%, 2% and 15% of the mass of the amphiphilic carbon dot mother liquor, respectively) were added to the above amphiphilic carbon dot mother liquor. After purging with nitrogen for 30 minutes, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (the amount added was 0.05% of the total mass of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid) was added and the reaction was initiated at 40 °C. After 6 hours, a milky white pressure-driven integrated working fluid was obtained.

[0041] The carbon dot mother liquor was dialyzed, freeze-dried, and then examined by transmission electron microscopy. Figure 1 The image shown is a transmission electron microscope (TEM) image of the amphiphilic carbon dots in this embodiment, which shows that their particle size is less than 10 nm.

[0042] Example 2 A method for preparing a pressure-driven integrated working fluid based on amphiphilic carbon dots, the specific steps of which are as follows: (1) Weigh 1 g of acrylamide, 0.2 g of 2-acrylamido-2-methylpropanesulfonic acid, 0.05 g of methacryloyloxydimethyldodecylammonium chloride, 0.05 g of N,N'-methylenebisacrylamide and 0.2 g of potassium persulfate respectively, dissolve them in 100 mL of deionized water, place them in a reaction vessel and react at 180 °C for 12 hours, then cool to obtain amphiphilic carbon dot mother liquor; (2) Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and sodium chloride (accounting for 25%, 2% and 15% of the mass of the amphiphilic carbon dot mother liquor, respectively) were added to the above amphiphilic carbon dot mother liquor. After purging with nitrogen for 30 minutes, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (the amount added was 0.05% of the total mass of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid) was added and the reaction was initiated at 40 °C. After 6 hours, a milky white pressure-driven integrated working fluid was obtained.

[0043] Example 3 A method for preparing a pressure-driven integrated working fluid based on amphiphilic carbon dots, the specific steps of which are as follows: (1) Weigh out 5 g of acrylamide, 0.05 g of 2-acrylamido-2-methylpropanesulfonic acid, 0.2 g of methacryloyloxydimethyldodecylammonium chloride, 0.2 g of N,N'-methylenebisacrylamide and 0.1 g of potassium persulfate, dissolve them in 100 mL of deionized water, place them in a reaction vessel and react at 180 °C for 12 hours, then cool to obtain amphiphilic carbon dot mother liquor; (2) Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and sodium chloride (accounting for 25%, 2% and 15% of the mass of the amphiphilic carbon dot mother liquor, respectively) were added to the above amphiphilic carbon dot mother liquor. After purging with nitrogen for 30 minutes, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (the amount added was 0.05% of the total mass of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid) was added and the reaction was initiated at 40 °C. After 6 hours, a milky white pressure-driven integrated working fluid was obtained.

[0044] Example 4 A method for preparing a pressure-driven integrated working fluid based on amphiphilic carbon dots, the specific steps of which are as follows: (1) Weigh 3 g of acrylamide, 0.15 g of 2-acrylamido-2-methylpropanesulfonic acid, 0.1 g of methacryloyloxydimethyldodecylammonium chloride, 0.12 g of N,N'-methylenebisacrylamide and 0.1 g of potassium persulfate respectively, dissolve them in 100 mL of deionized water, place them in a reaction vessel and react at 180 °C for 12 hours, then cool to obtain amphiphilic carbon dot mother liquor; (2) Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and sodium chloride (accounting for 15%, 1% and 10% of the mass of the amphiphilic carbon point mother liquor, respectively) were added to the above amphiphilic carbon point mother liquor. After purging with nitrogen for 30 minutes, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (the amount added was 0.05% of the total mass of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid) was added and the reaction was initiated at 40 °C. After 6 hours, a milky white pressure-driven integrated working fluid was obtained.

[0045] Example 5 A method for preparing a pressure-driven integrated working fluid based on amphiphilic carbon dots, the specific steps of which are as follows: (1) Weigh 3 g of acrylamide, 0.15 g of 2-acrylamido-2-methylpropanesulfonic acid, 0.1 g of methacryloyloxydimethyldodecylammonium chloride, 0.12 g of N,N'-methylenebisacrylamide and 0.1 g of potassium persulfate respectively, dissolve them in 100 mL of deionized water, place them in a reaction vessel and react at 180 °C for 12 hours, then cool to obtain amphiphilic carbon dot mother liquor; (2) Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and sodium chloride (accounting for 30%, 3% and 20% of the mass of the amphiphilic carbon point mother liquor, respectively) were added to the above amphiphilic carbon point mother liquor. After purging with nitrogen for 30 minutes, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (the amount added was 0.05% of the total mass of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid) was added and the reaction was initiated at 40 °C. After 6 hours, a milky white pressure-driven integrated working fluid was obtained.

[0046] Example 6 A method for preparing a pressure-driven integrated working fluid based on amphiphilic carbon dots, the specific steps of which are as follows: (1) Weigh 3 g of acrylamide, 0.15 g of 2-acrylamido-2-methylpropanesulfonic acid, 0.1 g of methacryloyloxydimethyldodecylammonium chloride, 0.12 g of N,N'-methylenebisacrylamide and 0.1 g of potassium persulfate respectively, dissolve them in 100 mL of deionized water, place them in a reaction vessel and react at 180 °C for 12 hours, then cool to obtain amphiphilic carbon dot mother liquor; (2) Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and sodium chloride (accounting for 25%, 2% and 15% of the mass of the amphiphilic carbon point mother liquor, respectively) were added to the above amphiphilic carbon point mother liquor. After purging with nitrogen for 30 minutes, ammonium persulfate / sodium bisulfite (mass ratio 1:2, the amount added is 0.05% of the total mass of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid) were added and the reaction was initiated at 10 °C. After 6 hours, a milky white pressure-driven integrated working fluid was obtained.

[0047] Comparative Example 1 After preparing a polyacrylamide dispersion according to Example 1 of patent CN104558406B, a petroleum sulfonate surfactant with a mass percentage of 10% was compounded to obtain a working solution.

[0048] Comparative Example 2 After preparing a polyacrylamide dispersion according to Example 1 of patent CN104558406B, a working solution was obtained by compounding 10% by mass of petroleum sulfonate / AEO9 surfactant (the mass ratio of the two surfactants was 1:1).

[0049] Comparative Example 3 Weigh out 3 g of acrylamide, 0.15 g of 2-acrylamido-2-methylpropanesulfonic acid, 0.1 g of methacryloyloxydimethyldodecylammonium chloride, 0.12 g of N,N'-methylenebisacrylamide, and 0.1 g of potassium persulfate, respectively, and dissolve them in 100 mL of deionized water. Place the solutions in a reaction vessel and react at 180 °C for 12 hours. After cooling, obtain an amphiphilic carbon dot mother liquor.

[0050] Comparative Example 4 Weigh out 25 g of acrylamide, 2 g of 2-acrylamido-2-methylpropanesulfonic acid, and 15 g of sodium chloride, dissolve them in 100 mL of deionized water, purge with nitrogen for 30 minutes, then add 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (0.05% of the total mass of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid) and initiate the reaction at 40 °C. After 6 hours, a milky white working solution is obtained.

[0051] Performance testing The working solutions prepared in each embodiment and comparative example were subjected to performance tests, and the test methods are as follows: (1) Measurement of interfacial tension: The interfacial tension between the oil phase and a 0.3% working solution (diluted to a concentration of 0.3%) was measured using a rotating drop interfacial tensiometer. Before testing, the quartz tube was cleaned sequentially with anhydrous ethanol and distilled water, and the instrument was calibrated. The prepared sample solution was injected into the quartz tube, followed by precise injection of an oil droplet using a microsyringe. Measurements were taken at 60 °C and a rotation speed of 6000 rpm, with interfacial tension values ​​recorded every 1 minute until three consecutive readings remained almost unchanged, indicating equilibrium had been reached. All data were measured independently and repeated three times, and the arithmetic mean was taken as the final result to ensure data reliability.

[0052] (2) Wetting performance test: The glass slide was immersed in a 1% hydrochloric acid solution for 4 hours, then rinsed with distilled water until neutral, and then ultrasonically cleaned with distilled water and ethanol for 5 minutes each, followed by drying in a 60°C oven. If a water droplet could spread on the glass slide, it indicated that the slide was clean. The cleaned glass slide was then immersed in dimethyl silicone oil and left to stand at 60°C for 3 days for oleophilic treatment. If a water droplet could roll on the glass slide after treatment, it indicated that the glass slide had changed from a hydrophilic to an oleophilic surface. The oleophilic-treated glass slide was then immersed in a 0.3% working solution system for 48 hours, and the contact angle of the water droplet on the glass slide surface was measured using a contact angle meter.

[0053] (3) Oil displacement performance test: The dynamic oil displacement performance of the system was evaluated using a core flow test system. The specific experimental procedure was as follows: First, 5 pore volumes (PV) of water were injected into the core at an injection rate of 2 mL / min, and the water phase permeability of the core was calculated according to Darcy's formula. Then, 10 PV of crude oil was injected at an injection rate of 2 mL / min until the core saturation oil content reached more than 98%, and the core with saturated crude oil was aged at 60 ℃ for 3 days. Next, 2 PV of mineralized water was injected at an injection rate of 0.1 mL / min, the oil production volume was recorded, and the waterflood recovery rate was calculated. At the same injection rate, 0.5 PV of a 0.3% working fluid system was injected, the oil production volume was recorded, and its enhanced oil recovery rate was calculated. Finally, 1 PV of mineralized water was injected at an injection rate of 2 mL / min for subsequent waterflooding.

[0054] (4) Drag reduction performance test: Inject the working fluid sample (diluted to a concentration of 0.5%) into the high-pressure pump, set a constant flow rate, and start the high-pressure pump to allow the working fluid to flow in a 4-meter-long, 1 / 2-inch-diameter pipe. Record the pressure values ​​at the pipe inlet and outlet. Using water instead of the working fluid, measure the inlet and outlet pressures of the blank group, and calculate the drag reduction rate of the working fluid according to the formula: ; ; In the formula: This indicates the pressure difference between the inlet and outlet of the pipeline, expressed in MPa. Indicates the inlet pressure of the pipeline, in MPa; Indicates the pipeline outlet pressure, in MPa; DR The drag reduction ratio is expressed as %; This indicates the pressure difference between the inlet and outlet of the clean water, expressed in MPa. This indicates the pressure difference between the inlet and outlet of the fracturing fluid, expressed in MPa.

[0055] The performance test results of the working fluids prepared in each embodiment and comparative example are shown in Table 1 below.

[0056] Table 1

[0057] Table 1 shows that the pressure-driven integrated working fluids prepared in Examples 1-6 of this invention simultaneously achieve high drag reduction performance and excellent oil displacement performance. Regarding interfacial tension, the interfacial tension of each example is significantly lower than that of Comparative Examples 1, 2, and 4, indicating that the introduction of amphiphilic carbon dots can effectively reduce the oil-water interfacial tension. In terms of wetting performance, the contact angle significantly decreased after immersion in the working fluids of each example, indicating an effective transformation from an oleophilic surface to a hydrophilic surface; in contrast, the comparative examples without amphiphilic carbon dot components show significantly insufficient wetting reversal ability. Figure 2These are photographs of the contact angle of the glass slide surface before and after treatment with the working solution in Example 1. It can be observed that before immersion, water droplets on the glass slide surface are spherical. Figure 2 (a) shows a contact angle of 86.0°, exhibiting obvious oleophilicity; after immersion in the working solution of Example 1 for 48 hours, the water droplets completely spread on the surface of the glass slide ( Figure 2 In (b) of the model, the contact angle drops to 33.0°, the surface properties change from oleophilic to hydrophilic, and the wetting reversal effect is significant.

[0058] Regarding enhanced oil recovery, the enhanced oil recovery rates of the embodiments were significantly higher than those of the comparative examples, indicating that the working fluid of the embodiments of the present invention can effectively strip residual oil from the rock surface and improve oil displacement efficiency through the synergistic effect of ultra-low interfacial tension, wetting reversal performance, and nano-effect. Regarding drag reduction performance, although Comparative Examples 1 and 2 exhibited some drag reduction performance, it was lower than that of the embodiments of the present invention; Comparative Example 3, lacking polymer thickening components, had a drag reduction rate of only 21.3%; and although Comparative Example 4 contained polymers, its drag reduction rate was also lower than that of the embodiments due to the lack of stabilizing effects from amphiphilic carbon points.

[0059] Based on the comprehensive performance evaluations, Comparative Examples 1 and 2, which used conventional polyacrylamide dispersions combined with surfactants, exhibited some drag reduction properties, but their interfacial tension and wetting reversal performance were significantly insufficient, resulting in low oil displacement efficiency. Furthermore, compatibility issues existed between the two functional components, making true "pressure-driven oil displacement integration" difficult to achieve. Comparative Example 3 only prepared amphiphilic carbon dot mother liquor without subsequent polymerization. Although it had low interfacial tension, it lacked a polymer network structure, resulting in extremely poor drag reduction performance and unsatisfactory oil recovery. Comparative Example 4, without adding amphiphilic carbon dots, directly underwent aqueous dispersion polymerization, resulting in a working fluid with an interfacial tension as high as 2.36 mN / m, poor wetting reversal performance, and limited oil recovery improvement. The amphiphilic carbon dot-based pressure-driven oil displacement working fluid provided in this invention, through the surface activity and nano-effect of amphiphilic carbon dots combined with the polymer network structure formed by aqueous dispersion polymerization, achieves a synergistic effect of ultra-low interfacial tension, wetting reversal performance, nano-effect, and high drag reduction performance.

[0060] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method for preparing an integrated pressure-driven working fluid based on amphiphilic carbon dots, characterized in that, Includes the following steps: The first nonionic monomer, the first salt-tolerant anionic monomer, the long carbon chain cationic monomer, the crosslinking agent and the first initiator are dissolved in water and subjected to a hydrothermal reaction at 160~200℃. After cooling, an amphiphilic carbon dot mother liquor is obtained. A second nonionic monomer, a second salt-resistant anionic monomer, an inorganic salt, and a second initiator are added to the amphiphilic carbon dot mother liquor to carry out a polymerization reaction and obtain a pressure-driven integrated working fluid. The first nonionic monomer includes acrylamide and / or methacrylamide; The first salt-resistant anionic monomer includes at least one of allyl sulfonic acid, methyl allyl sulfonic acid, vinyl sulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid; The long-chain cationic monomer includes at least one of methacryloyloxydimethyloctylammonium chloride, methacryloyloxydimethyldodecylammonium chloride, and methacryloyloxydimethylhexadecylammonium chloride. The crosslinking agent includes at least one of N,N'-methylenebisacrylamide, ethyl bisacrylate, and polyethylene glycol diacrylate. The first initiator includes at least one of potassium persulfate, benzoyl peroxide, azobisisobutyronitrile, and azodialkylamidine; The second nonionic monomer includes acrylamide and / or methacrylamide; The second salt-resistant anionic monomer includes at least one of allyl sulfonic acid, methyl allyl sulfonic acid, vinyl sulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid; The second initiator is an azo initiator or a redox initiator.

2. The method for preparing an integrated pressure-driven working fluid based on amphiphilic carbon points according to claim 1, characterized in that, The ratio of the first nonionic monomer to water is (1~5) g: 100 mL; And / or, the ratio of the first salt-resistant anionic monomer to water is (0.05~0.2) g: 100 mL; And / or, the ratio of the long-chain cationic monomer to water is (0.05~0.2) g: 100 mL; And / or, the crosslinking agent to water ratio is (0.05~0.2) g: 100 mL; And / or, the ratio of the first initiator to water is (0.05~0.2) g: 100 mL.

3. The method for preparing an integrated pressure-driven working fluid based on amphiphilic carbon dots according to claim 1, characterized in that, The hydrothermal reaction takes 12 to 24 hours.

4. The method for preparing an integrated pressure-driven working fluid based on amphiphilic carbon dots according to claim 1, characterized in that, The inorganic salt includes at least one of sodium chloride, ammonium chloride, sodium sulfate, and ammonium sulfate; And / or, the mass of the second nonionic monomer accounts for 15% to 30% of the mass of the amphiphilic carbon dot mother liquor; And / or, the mass of the second salt-resistant anionic monomer accounts for 1% to 3% of the mass of the amphiphilic carbon dot mother liquor; And / or, the inorganic salt accounts for 10% to 20% of the mass of the amphiphilic carbon dot mother liquor.

5. The method for preparing an integrated pressure-driven working fluid based on amphiphilic carbon points according to claim 1, characterized in that, The amount of the second initiator added is 0.001% to 0.1% of the total mass of the second nonionic monomer and the second salt-resistant anionic monomer.

6. The method for preparing an integrated pressure-driven working fluid based on amphiphilic carbon dots according to claim 1, characterized in that, The azo initiator includes 2,2'-azobisisobutylamidine dihydrochloride or 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride.

7. The method for preparing an integrated pressure-driven working fluid based on amphiphilic carbon dots according to claim 1, characterized in that, The redox initiator is composed of an oxidant and a reducing agent; the oxidant includes any one of ammonium persulfate, sodium persulfate, and potassium persulfate; the reducing agent includes any one of sodium bisulfite and sodium sulfite; the mass ratio of the oxidant to the reducing agent is (1~1.5):

2.

8. The method for preparing an integrated pressure-driven working fluid based on amphiphilic carbon points according to claim 1, characterized in that, When the second initiator is an azo initiator, the polymerization temperature is 40~60℃; when the second initiator is a redox initiator, the polymerization temperature is 0~30℃.

9. A pressure-driven integrated working fluid based on amphiphilic carbon dots, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 8.

10. The application of the pressure-driven integrated working fluid based on amphiphilic carbon points as described in claim 9 in crude oil recovery.

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