Emulsion modified fracturing fluid and preparation method thereof

Abstract

The invention provides an emulsion modified fracturing fluid and a preparation method thereof, and relates to the field of fracturing fluids. Comprising the following raw materials: 10-20% of modified polyacrylamide, 2-5% of modified sodium carboxymethyl cellulose, 2-5% of carboxylated silicon quantum dots, 1-2% of a cross-linking agent, 1-5% of a surfactant, 1-2% of an initiator, 1-2% of a defoaming agent and the balance of water. Wherein the modified polyacrylamide is obtained by carrying out emulsion polymerization on an acrylamide monomer, 2-acrylamide-2-methylpropanesulfonic acid and a C5-C10 straight-chain quaternary ammonium salt; the modified sodium carboxymethyl cellulose is obtained by carrying out intercalation reaction on montmorillonite and sodium carboxymethyl cellulose. The sulfonic acid group in the modified polyacrylamide can improve the high temperature resistance of the fracturing fluid, the C5-C10 straight-chain quaternary ammonium salt provides antibacterial quaternary ammonium salt for the fracturing fluid, and the straight-chain structure can improve the hydrophobicity of a three-dimensional network structure; and the C5-C10 straight chains can also form intermolecular and intramolecular association effects with the sodium carboxymethyl cellulose, so that the salt resistance of the fracturing fluid is improved.

Description

Technical Field

[0001] The present invention relates to the field of fracturing fluid, and in particular to an emulsion-modified fracturing fluid and a preparation method thereof. Background Art

[0002] Fracturing fluid is a key engineering fluid in the development of oil and gas fields. It is injected into oil wells at high pressure to form artificial fractures and carry proppants (such as quartz sand and ceramsite) to maintain the conductivity of fractures, thereby significantly increasing the production of oil and gas wells. Its mechanism of action includes: transmitting pressure: transmitting high pressure from the ground to the formation to form a complex fracture network; transporting proppants: ensuring that the fractures can still maintain high permeability channels after pressure is released; compatible with formations: it needs to be compatible with reservoir rocks and fluid chemistry to avoid damage.

[0003] Fracturing fluids can be divided into water-based fracturing fluids, oil-based fracturing fluids, foam fracturing fluids, etc. according to their composition. Water-based fracturing fluids such as guar gum-based fluids have a sharp drop in viscosity in formations above 80°C, which results in an accelerated sedimentation rate of proppants (such as ceramsite), a decrease in the fracture support effect, and difficulty in completely degrading polymer chains for breaking the gel, and residues will clog the pores. Oil-based fracturing fluids are expensive, require special sand mixing equipment, and have a low flash point, which poses a risk of fire and explosion. Foam fracturing fluids have poor sand-carrying capacity and are prone to sand plugging.

[0004] Water-based fracturing fluid has the advantages of strong sand carrying capacity, high safety factor, and low cost, but its high temperature resistance is poor and it is easy to fail at high temperatures. Patent CN118853131B discloses an emulsion-modified fracturing fluid for oil well protection and its preparation method, which uses emulsion-modified polyacrylamide, high-efficiency cross-linking agent, surfactant, potassium chloride, water, etc. as raw materials, wherein the emulsion-modified polyacrylamide introduces sulfonic acid monomers and fluorine-containing monomers into the polyacrylamide group, which improves the high temperature resistance and salt resistance of the fracturing fluid. However, the viscosity and sand carrying capacity of the fracturing fluid of this scheme need to be improved. Summary of the invention

[0005] The object of the present invention is to provide an emulsion-modified fracturing fluid with high viscosity, good high temperature resistance, good salt resistance and strong sand carrying capacity.

[0006] Another object of the present invention is to provide a method for preparing an emulsion-modified fracturing fluid, wherein the fracturing fluid prepared by the method has good temperature resistance and salt resistance.

[0007] The present invention solves the technical problem by adopting the following technical solutions.

[0008] In one aspect, an embodiment of the present invention provides an emulsion-modified fracturing fluid, which comprises the following raw materials by mass fraction: Modified polyacrylamide 10-20%, modified sodium carboxymethyl cellulose 2-5%, carboxylated silicon quantum dots 2-5%, crosslinking agent 1-2%, surfactant 1-5%, initiator 1-2%, defoaming agent 1-2%, and the balance is water; Wherein, the modified polyacrylamide is obtained by emulsion polymerization of acrylamide monomer, 2-acrylamide-2-methylpropane sulfonic acid, and C5-C10 linear quaternary ammonium salt; The modified sodium carboxymethyl cellulose is obtained by intercalation reaction of montmorillonite and sodium carboxymethyl cellulose.

[0009] In some embodiments of the present invention, the modified polyacrylamide is prepared as follows: Acrylamide monomer, 2-acrylamide-2-methylpropane sulfonic acid, C5-C10 straight-chain quaternary ammonium salt, sodium dodecyl sulfate and water are stirred and mixed evenly, and potassium persulfate is added, and stirred until the reaction is completed, and the mixture is allowed to stand and filtered to obtain the modified polyacrylamide.

[0010] In some embodiments of the present invention, the molar ratio of the acrylamide monomer, 2-acrylamide-2-methylpropane sulfonic acid, and C5-C10 linear quaternary ammonium salt is 1:(0.5-1):(0.8-1.2).

[0011] In some embodiments of the present invention, the C5-C10 straight-chain quaternary ammonium salt is one or more of N,N,N-trimethylpentyl ammonium chloride, N,N,N-trimethylhexyl ammonium bromide, N,N-dimethylethylpentyl ammonium chloride, N,N-dimethylpropylhexyl ammonium bromide, N,N,N-trimethylheptyl ammonium hydrogen sulfate, and N,N,N-trimethyloctyl ammonium nitrate.

[0012] In some embodiments of the present invention, the modified sodium carboxymethyl cellulose is prepared by the following method: Mix montmorillonite with water, disperse by ultrasonic for 10-20 min, add NaCl solution, and stir evenly; Then, add the sodium carboxymethyl cellulose solution, raise the temperature to 40-60° C., stir for 2-4 hours, let stand, and filter to obtain the modified sodium carboxymethyl cellulose.

[0013] In some embodiments of the present invention, the molar ratio of the montmorillonite to the sodium carboxymethyl cellulose is 1:(0.5-0.8). In some embodiments of the present invention, the cross-linking agent is organic zirconium or organic titanium, such as tetrabutyl titanate.

[0014] In some embodiments of the present invention, the surfactant is a mixture of one or more of Span 70, Tween 80, and sodium dodecylbenzene sulfonate.

[0015] In some embodiments of the present invention, the initiator is one of benzoyl peroxide, lauroyl peroxide, potassium persulfate, ammonium persulfate, sodium perbromide and hydrogen peroxide.

[0016] On the other hand, an embodiment of the present invention provides a method for preparing an emulsion-modified fracturing fluid, comprising: The modified polyacrylamide, modified sodium carboxymethyl cellulose and carboxylated silicon quantum dots are mixed with water and stirred evenly, and then ultrasonically dispersed for 10 minutes, and then a cross-linking agent, a surfactant, an initiator and a defoaming agent are added and stirred evenly.

[0017] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects: The fracturing fluid provided by the invention uses modified polyacrylamide and modified sodium carboxymethyl cellulose as main raw materials. Under the action of a crosslinking agent and an initiator, the fracturing fluid can be crosslinked to form a three-dimensional network structure after entering an oil well. The sulfonic acid group in the modified polyacrylamide can improve the high temperature resistance of the fracturing fluid. The straight chain of the C5-C10 straight chain quaternary ammonium salt can be embedded in the three-dimensional network structure of the polyacrylamide, which not only provides the fracturing fluid with a quaternary ammonium salt with antibacterial properties, but also improves the hydrophobicity of the three-dimensional network structure. The C5-C10 straight chain can also form an intermolecular and intramolecular association effect with the sodium carboxymethyl cellulose to extend the molecular chain, so that the three-dimensional network structure is grafted with a longer molecular chain with a sodium carboxymethyl group. The sodium carboxymethyl has excellent salt resistance, thereby improving the salt resistance of the fracturing fluid.

[0018] On the other hand, modified sodium carboxymethyl cellulose is obtained by intercalation reaction of montmorillonite and sodium carboxymethyl cellulose, that is, the molecular chain of sodium carboxymethyl cellulose is inserted into the molecular layer of montmorillonite, making the combination of the two closer. Montmorillonite expands after absorbing water, which can support the three-dimensional network structure of the fracturing fluid and increase the viscosity of the fracturing fluid.

[0019] Carboxylated silicon quantum dots are added to the fracturing fluid, which provide many active sites. The carboxylated silicon quantum dots form a complex three-dimensional network structure with organic titanium or organic zirconium and polyacrylamide, which increases the viscosity of the fracturing fluid in the oil well and thus improves the fracturing effect. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0021] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0022] The embodiment of the present invention provides an emulsion-modified fracturing fluid, which comprises the following raw materials by mass fraction: 10-20% modified polyacrylamide, 2-5% modified sodium carboxymethyl cellulose, 2-5% carboxylated silicon quantum dots, 1-2% crosslinking agent, 1-5% surfactant, 1-2% initiator, 1-2% defoaming agent, and the balance is water; wherein the modified polyacrylamide is obtained by emulsion polymerization of acrylamide monomer, 2-acrylamide-2-methylpropane sulfonic acid, and C5-C10 straight-chain quaternary ammonium salt; and the modified sodium carboxymethyl cellulose is obtained by intercalation reaction of montmorillonite and sodium carboxymethyl cellulose.

[0023] Specifically, the modified polyacrylamide is prepared according to the following method: The acrylamide monomer, 2-acrylamide-2-methylpropane sulfonic acid, C5-C10 linear quaternary ammonium salt, sodium dodecyl sulfate and water are stirred and mixed evenly, and then potassium persulfate is added, stirred until the reaction is completed, and the mixture is allowed to stand and filtered to obtain the modified polyacrylamide. The molar ratio of the acrylamide monomer, 2-acrylamide-2-methylpropane sulfonic acid and C5-C10 linear quaternary ammonium salt is 1: (0.5-1): (0.8-1.2). The modified polyacrylamide is grafted with sulfonic acid groups and linear ammonium salts. The sulfonic acid groups can improve the high temperature resistance of the fracturing fluid, the linear structure can improve the hydrophobicity of polyacrylamide, and the ammonium salt groups can provide the antibacterial property of the fracturing fluid, thereby preventing microorganisms from decomposing the fracturing fluid during use and affecting the use effect of the fracturing fluid. The molar ratio of acrylamide monomer, 2-acrylamide-2-methylpropane sulfonic acid and C5-C10 straight-chain quaternary ammonium salt is 1:(0.5-1):(0.8-1.2), and preferably, the molar ratio is 1:0.5:1.2.

[0024] Specifically, the modified sodium carboxymethyl cellulose is prepared by the following method: Mix montmorillonite with water, disperse by ultrasonic for 10-20 min, add NaCl solution, and stir evenly; Then add sodium carboxymethyl cellulose solution, heat to 40-60°C, stir for 2-4h, stand and filter to obtain the modified sodium carboxymethyl cellulose. Wherein, the molar ratio of the montmorillonite to the sodium carboxymethyl cellulose is 1: (0.5-0.8). Montmorillonite will swell in water, increase the interlayer spacing, and increase the probability of sodium carboxymethyl cellulose molecules inserting into the interlayer of montmorillonite. By inserting sodium carboxymethyl cellulose, the combination of montmorillonite and sodium carboxymethyl cellulose is made tighter. Under the action of the cross-linking agent, the molecules of sodium carboxymethyl cellulose can be cross-linked and entangled with polyacrylamide, further improving the strength of the three-dimensional network structure connection between montmorillonite and polyacrylamide. During use, the fracturing fluid enters the oil well, and the montmorillonite further absorbs water and expands, which can play a role in supporting the three-dimensional network structure of the fracturing fluid and increase the viscosity of the fracturing fluid. The sodium carboxymethyl cellulose inserted into the montmorillonite interlayer can provide the viscosity and sand carrying capacity of the fracturing fluid, reduce filtration, protect the oil and gas layer, and reduce the damage of the fracturing fluid to the oil and gas layer.

[0025] The raw materials used in the embodiments of the present invention are directly purchased from the market, wherein the C5-C10 straight-chain quaternary ammonium salt is one or more of N,N,N-trimethylpentyl ammonium chloride, N,N,N-trimethylhexyl ammonium bromide, N,N-dimethylethylpentyl ammonium chloride, N,N-dimethylpropylhexyl ammonium bromide, N,N,N-trimethylheptyl ammonium hydrogen sulfate, and N,N,N-trimethyloctyl ammonium nitrate.

[0026] The crosslinking agent is organic zirconium or organic titanium, such as zirconate (tetrabutyl zirconate, tetrapropyl zirconate), titanate (tetrabutyl titanate, trioleyl isopropyl titanate, triisostearoyl isopropyl titanate, isopropyl tri(dioctyl pyrophosphate) titanate, etc.). Preferably, the crosslinking agent is tetrabutyl titanate.

[0027] The surfactant is a mixture of one or more of Span 70, Tween 80, and sodium dodecylbenzene sulfonate. The initiator is one of benzoyl peroxide, lauroyl peroxide, potassium persulfate, ammonium persulfate, sodium perbromate, and hydrogen peroxide. The defoamer is one of LT-130 defoamer and LT-8120 defoamer.

[0028] The preparation method of the emulsion-modified fracturing fluid is as follows: The modified polyacrylamide, modified sodium carboxymethyl cellulose and carboxylated silicon quantum dots are mixed with water and stirred evenly, and then ultrasonically dispersed for 10 minutes, and then a cross-linking agent, a surfactant, an initiator and a defoaming agent are added and stirred evenly.

[0029] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0030] Example The modified polyacrylamide and modified sodium carboxymethyl cellulose used in each example were prepared according to the following methods, and the remaining raw materials were directly purchased from the market.

[0031] 1. Prepare modified polyacrylamide A as follows: The modified polyacrylamide is obtained by stirring and mixing acrylamide monomer, 2-acrylamide-2-methylpropanesulfonic acid, C5-C10 linear quaternary ammonium salt, sodium dodecyl sulfate and water, and then adding potassium persulfate, stirring until the reaction is completed, standing and filtering. The molar ratio of the acrylamide monomer, 2-acrylamide-2-methylpropanesulfonic acid and C5-C10 linear quaternary ammonium salt is 1:0.5:1.2.

[0032] 2. Prepare modified polyacrylamide B as follows: The modified polyacrylamide is obtained by stirring and mixing acrylamide monomer, 2-acrylamide-2-methylpropanesulfonic acid, C5-C10 linear quaternary ammonium salt, sodium dodecyl sulfate and water, and then adding potassium persulfate, stirring until the reaction is completed, standing and filtering. The molar ratio of the acrylamide monomer, 2-acrylamide-2-methylpropanesulfonic acid and C5-C10 linear quaternary ammonium salt is 1:1:1.2.

[0033] 3. Prepare modified polyacrylamide C as follows: The modified polyacrylamide is obtained by stirring and mixing acrylamide monomer, 2-acrylamide-2-methylpropanesulfonic acid, C5-C10 linear quaternary ammonium salt, sodium dodecyl sulfate and water, and then adding potassium persulfate, stirring until the reaction is completed, standing and filtering. The molar ratio of acrylamide monomer, 2-acrylamide-2-methylpropanesulfonic acid and C5-C10 linear quaternary ammonium salt is 1:0.5:0.8.

[0034] 4. Prepare modified sodium carboxymethyl cellulose D as follows: Mix montmorillonite with water, disperse by ultrasonic for 20 minutes, add NaCl solution, stir evenly, then add sodium carboxymethyl cellulose solution, heat to 60°C, stir for 3 hours, let stand, filter, and obtain the modified sodium carboxymethyl cellulose. The molar ratio of montmorillonite to sodium carboxymethyl cellulose is 1:0.8. 5. Prepare modified sodium carboxymethyl cellulose E as follows: Mix montmorillonite with water, disperse by ultrasonic for 15 minutes, add NaCl solution, stir evenly, then add sodium carboxymethyl cellulose solution, heat to 50°C, stir for 3 hours, let stand, filter, and obtain the modified sodium carboxymethyl cellulose. The molar ratio of montmorillonite to sodium carboxymethyl cellulose is 1:0.5.

[0035] 6. Prepare modified sodium carboxymethyl cellulose F as follows: Mix montmorillonite with water, disperse by ultrasonic for 20 minutes, add NaCl solution, stir evenly, then add sodium carboxymethyl cellulose solution, heat to 60°C, stir for 3 hours, let stand, filter, and obtain the modified sodium carboxymethyl cellulose. The molar ratio of montmorillonite to sodium carboxymethyl cellulose is 1:0.6.

[0036] Based on the modified polyacrylamide and modified sodium carboxymethyl cellulose prepared by the above method, and other raw materials purchased on the market, the fracturing fluids of various embodiments were prepared according to the following raw material ratios and preparation methods.

[0037] Example 1-6: According to the ratio in Table 1, the raw materials of the fracturing fluid of Example 1-6 were prepared.

[0038] Table 1 Raw material ratios of Examples 1-6 (mass percentage %)

[0039] Among them, in the above-mentioned embodiments 1-6, modified polyacrylamide A and modified sodium carboxymethyl cellulose D were used, the crosslinking agent was tetrabutyl titanate, the initiator was benzoyl peroxide, the surfactant was Span 70, and the defoaming agent was LT-130 defoaming agent.

[0040] According to the following method, based on the raw material ratios in Table 1, the fracturing fluids of Examples 1-6 were prepared: The modified polyacrylamide, modified sodium carboxymethyl cellulose and carboxylated silicon quantum dots are mixed with water and stirred evenly, and then ultrasonically dispersed for 10 minutes, and then a cross-linking agent, a surfactant, an initiator and a defoaming agent are added and stirred evenly.

[0041] Example 7: The difference from Example 1 is that in this example, modified polyacrylamide B is used, and the rest of the raw materials and preparation methods are the same as those in Example 1.

[0042] Example 8: The difference from Example 1 is that in this example, modified polyacrylamide C is used, and the rest of the raw materials and preparation methods are the same as those in Example 1.

[0043] Example 9: The difference from Example 1 is that in this example, modified sodium carboxymethyl cellulose E is used, and the remaining raw materials and preparation methods are the same as those in Example 1.

[0044] Example 10: The difference from Example 1 is that in this example, modified sodium carboxymethyl cellulose F is used, and the remaining raw materials and preparation methods are the same as those in Example 1.

[0045] Example 11: The difference from Example 1 is that in this example, modified polyacrylamide B and modified sodium carboxymethyl cellulose E are used, and the remaining raw materials and preparation methods are the same as those in Example 1.

[0046] Example 12: The difference from Example 1 is that in this example, modified polyacrylamide C and modified sodium carboxymethyl cellulose F are used, and the remaining raw materials and preparation methods are the same as those in Example 1.

[0047] Comparative Example 1 The difference from Example 1 is that sodium carboxymethyl cellulose is used as the raw material instead of the modified sodium carboxymethyl cellulose in Example 1, and the remaining raw materials and preparation method are the same as those in Example 1.

[0048] Comparative Example 2 The difference from Example 1 is that no carboxylated silicon quantum dots are added to the raw materials, and the remaining raw materials and preparation methods are the same as those in Example 1.

[0049] Comparative Example 3 The difference from Example 1 is that sodium carboxymethyl cellulose is used in the raw material instead of the modified sodium carboxymethyl cellulose in Example 1, and no carboxylated silicon quantum dots are added. The remaining raw materials and preparation methods are the same as those in Example 1.

[0050] Comparative Example 4 The fracturing fluid was prepared by the method described in Example 3 in the specification of the patent CN202411348366.8.

[0051] Experimental example According to SY / T 5107-2005 "Evaluation Method for Water-Based Fracturing Fluid Performance", the heat and shear resistance of the fracturing fluids in Examples 1-6 and Comparative Examples 1-4 were tested, and the shear rate of the rheometer was set to 170 s -1 The temperature was raised linearly from 30°C to 200°C within 20 min. The results are shown in Table 2.

[0052] Table 2 Viscosity of each fracturing fluid at different temperatures (mPa·s)

[0053] It can be concluded from Table 2 that the fracturing fluid provided by the embodiment of the present invention has a viscosity that gradually decreases with increasing temperature, but still has a relatively high viscosity at 170-200° C., indicating that the fracturing fluid of the embodiment has good high temperature resistance, the polymer chain is not easily decomposed at high temperature, and still has excellent supporting strength and sand carrying capacity.

[0054] In Comparative Example 1, sodium carboxymethyl cellulose was not modified, that is, montmorillonite was not added to the fracturing fluid. It can be concluded from Table 2 that the viscosity of the fracturing fluid is low, and the viscosity decreases rapidly at high temperatures due to the lack of support from montmorillonite, which leads to a decrease in viscosity. In Comparative Example 2, carboxylated silicon quantum dots were not added, and the three-dimensional network structure formed was simple. As the temperature increased, the three-dimensional network structure was destroyed, and the viscosity of the fracturing fluid decreased. In Comparative Example 3, sodium carboxymethyl cellulose was not modified with montmorillonite and carboxylated silicon quantum dots were not added, and its viscosity at high temperatures was the lowest.

[0055] In summary, the fracturing fluid provided by the embodiment of the present invention uses modified polyacrylamide and modified sodium carboxymethyl cellulose as main raw materials. Under the action of a cross-linking agent and an initiator, after entering the oil well, it can be cross-linked to form a three-dimensional network structure. The sulfonic acid group in the modified polyacrylamide can improve the high temperature resistance of the fracturing fluid. The straight chain of the C5-C10 straight-chain quaternary ammonium salt can be embedded in the three-dimensional network structure of the polyacrylamide, which not only provides a quaternary ammonium salt with antibacterial properties for the fracturing fluid, but also the straight chain structure can improve the hydrophobicity of the three-dimensional network structure; and the C5-C10 straight chain can also form an intermolecular and intramolecular association effect with sodium carboxymethyl cellulose, extend the molecular chain, so that the three-dimensional network structure is grafted with a longer molecular chain with a sodium carboxymethyl group, and sodium carboxymethyl has excellent salt resistance, thereby improving the salt resistance of the fracturing fluid.

[0056] On the other hand, modified sodium carboxymethyl cellulose is obtained by intercalation reaction of montmorillonite and sodium carboxymethyl cellulose, that is, the molecular chain of sodium carboxymethyl cellulose is inserted into the molecular layer of montmorillonite, making the combination of the two closer. Montmorillonite expands after absorbing water, which can support the three-dimensional network structure of the fracturing fluid and increase the viscosity of the fracturing fluid.

[0057] The embodiments described above are part of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. An emulsion-modified fracturing fluid, characterized in that: Calculated by mass fraction, including the following raw materials: Modified polyacrylamide 10-20%, modified sodium carboxymethyl cellulose 2-5%, carboxylated silicon quantum dots 2-5%, crosslinking agent 1-2%, surfactant 1-5%, initiator 1-2%, defoaming agent 1-2%, and the balance is water; Wherein, the modified polyacrylamide is obtained by emulsion polymerization of acrylamide monomer, 2-acrylamide-2-methylpropane sulfonic acid, and C5-C10 linear quaternary ammonium salt; The modified sodium carboxymethyl cellulose is obtained by intercalation reaction of montmorillonite and sodium carboxymethyl cellulose.

2. The emulsion-modified fracturing fluid according to claim 1, characterized in that: The modified polyacrylamide is prepared as follows: Acrylamide monomer, 2-acrylamide-2-methylpropane sulfonic acid, C5-C10 straight-chain quaternary ammonium salt, sodium dodecyl sulfate and water are stirred and mixed evenly, and potassium persulfate is added, and stirred until the reaction is completed, and the mixture is allowed to stand and filtered to obtain the modified polyacrylamide.

3. The emulsion-modified fracturing fluid according to claim 1, characterized in that: The molar ratio of the acrylamide monomer, 2-acrylamide-2-methylpropane sulfonic acid and C5-C10 straight-chain quaternary ammonium salt is 1:(0.5-1):(0.8-1.2).

4. The emulsion-modified fracturing fluid according to claim 1, characterized in that: The C5-C10 straight-chain quaternary ammonium salt is one or more of N,N,N-trimethylpentyl ammonium chloride, N,N,N-trimethylhexyl ammonium bromide, N,N-dimethylethylpentyl ammonium chloride, N,N-dimethylpropylhexyl ammonium bromide, N,N,N-trimethylheptyl ammonium hydrogen sulfate, and N,N,N-trimethyloctyl ammonium nitrate.

5. The emulsion-modified fracturing fluid according to claim 1, characterized in that: The modified sodium carboxymethyl cellulose is prepared by the following method: Mix montmorillonite with water, disperse by ultrasonic for 10-20 min, add NaCl solution, and stir evenly; Then, add the sodium carboxymethyl cellulose solution, raise the temperature to 40-60° C., stir for 2-4 hours, let stand, and filter to obtain the modified sodium carboxymethyl cellulose.

6. The emulsion-modified fracturing fluid according to claim 5, characterized in that: The molar ratio of the montmorillonite to the sodium carboxymethyl cellulose is 1:(0.5-0.8).

7. The emulsion-modified fracturing fluid according to claim 1, characterized in that: The crosslinking agent is tetrabutyl titanate.

8. The emulsion-modified fracturing fluid according to claim 1, characterized in that: The surfactant is a mixture of one or more of Span 70, Tween 80 and sodium dodecylbenzene sulfonate.

9. The emulsion-modified fracturing fluid according to claim 1, characterized in that: The initiator is one of benzoyl peroxide, lauroyl peroxide, potassium persulfate, ammonium persulfate, sodium perbromide and hydrogen peroxide.

10. A method for preparing an emulsion-modified fracturing fluid according to any one of claims 1 to 9, characterized in that: It includes: The modified polyacrylamide, modified sodium carboxymethyl cellulose and carboxylated silicon quantum dots are mixed with water and stirred evenly, and then ultrasonically dispersed for 10 minutes, and then a cross-linking agent, a surfactant, an initiator and a defoaming agent are added and stirred evenly.

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