High-temperature-resistant clean fracturing fluid and preparation method thereof

Abstract

The invention discloses a high-temperature-resistant clean fracturing fluid and a preparation method thereof, and the high-temperature-resistant clean fracturing fluid comprises the following components in percentage by weight: 2.5-4% of a thickening agent, 0.2-0.5% of an anti-swelling agent, 0.8-2% of a counter ion auxiliary agent, 0.3-0.5% of a temperature-resistant stabilizer and the balance of water. The thickening agent is prepared by mixing a high-temperature-resistant biquaternary ammonium salt surfactant and erucamide propyl betaine in a mass ratio of (4.5-8): (2-5.5). The high-temperature-resistant clean fracturing fluid has the characteristics of thorough gel breaking and strong high-temperature resistance, can improve the fracturing effect of low-permeability and high-temperature reservoirs, and provides technical support for fracturing of high-temperature and low-permeability oil and gas reservoirs.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field fracturing, and particularly relates to a high-temperature resistant clean fracturing fluid and a preparation method thereof. Background Art

[0002] Hydraulic fracturing technology is to inject fracturing fluid into the formation to expand the fractures in the formation and create new fractures and fill them with proppants, thereby increasing the permeability of the formation. Among them, since the fracturing fluid has the functions of transmitting pressure, forming formation fractures and carrying proppants into the fractures, it has become a key factor affecting the fracturing effect. The prominent feature of oil and gas resources in China is that low-permeability oil and gas reservoirs are widely distributed and have large reserves, and high-temperature and low-permeability oil and gas reservoirs are even more common.

[0003] Currently, the commonly used fracturing fluids are high-molecular guar gum polysaccharides or their modified products. The residue content of such fracturing fluids is still relatively high, and these residues will cause irreparable damage to the permeability of the fracture support zone and the formation permeability of the fracturing, seriously affecting the fracturing stimulation effect. Based on this, Schlunberger Company has developed a new technology for fracturing stimulation in oil and gas wells, namely cationic VES clean fracturing fluid. This fracturing fluid is a polymer-free viscoelastic surfactant type fracturing fluid. The viscoelastic surfactant is the result of the association and aggregation of small molecules. It becomes a spherical low-viscosity liquid after encountering oil, thereby realizing automatic gel breaking and causing little damage to the formation. However, its temperature resistance is poor and it cannot adapt to high-temperature reservoirs. Therefore, it is urgent to develop a composite fracturing fluid with low cost, low damage and high temperature resistance for fracturing of high-temperature and low-permeability oil and gas reservoirs. Summary of the Invention

[0004] In view of the above problems, the present invention aims to provide a high-temperature resistant clean fracturing fluid and a preparation method thereof.

[0005] The technical solution of the present invention is as follows:

[0006] On the one hand, a high-temperature resistant clean fracturing fluid is provided, which includes 2.5-4% of thickening agent, 0.2-0.5% of swelling inhibitor, 0.8-2% of counterion assistant, 0.3-0.5% of temperature-resistant stabilizer, and the balance is water.

[0007] Preferably, the thickening agent is composed of a high-temperature resistant bisquaternary ammonium salt surfactant and erucic acid amide propyl betaine with a mass ratio of 4.5-8:2-5.5.

[0008] Preferably, the structural general formula of the high-temperature resistant bisquaternary ammonium salt surfactant is:

[0009]

[0010] In the formula: R is C8-C 16 alkyl.

[0011] Preferably, the high-temperature resistant bisquaternary ammonium salt surfactant is prepared by the following steps:

[0012] Mix N-methylethanolamine, dimethyl phthalate, and a solvent, stir evenly, and let stand at room temperature for 5 - 6 h to obtain an intermediate product;

[0013] Add an alkyl bromide to the intermediate product, stir evenly, and react at 40 - 60 °C for 10 - 12 h to obtain a product;

[0014] Dry the product to obtain the high-temperature resistant bisquaternary ammonium salt surfactant.

[0015] Preferably, the molar ratio of N-methylethanolamine to dimethyl phthalate is 2 - 2.2:0.8 - 1, the volume ratio of the solvent to N-methylethanolamine and dimethyl phthalate is 3 - 4:1, and the molar ratio of the alkyl bromide to dimethyl phthalate is 2 - 2.1:0.9 - 1.

[0016] Preferably, the swelling inhibitor is a potassium salt.

[0017] Preferably, the potassium salt is any one or more of potassium chloride, potassium acetate, and potassium bromide.

[0018] Preferably, the counterion assistant is any one or more of sodium toluenesulfonate, sodium salicylate, sodium dodecyl sulfate, sodium citrate, and sodium dioctyl sulfosuccinate.

[0019] Preferably, the temperature-resistant stabilizer is any one or more of sodium thiosulfate, sodium dodecyl sulfonate, and diethyltoluenediamine.

[0020] On the other hand, a preparation method of the high-temperature resistant clean fracturing fluid according to any one of the above is also provided, including the following steps: Add a thickening agent, a swelling inhibitor, a counterion assistant, and a temperature-resistant stabilizer to water in sequence under stirring conditions according to a ratio, and obtain the high-temperature resistant clean fracturing fluid after thickening.

[0021] The beneficial effects of the present invention are:

[0022] The high-temperature resistant clean fracturing fluid of the present invention has the characteristics of complete gel breaking and strong high-temperature resistance, can improve the fracturing effect of low-permeability and high-temperature reservoirs, and provides technical support for fracturing high-temperature and low-permeability oil and gas reservoirs. Description of the Drawings

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0024] Figure 1 Schematic diagram of the formation of a network structure by worm-like micelles of the high-temperature resistant gemini surfactant of the present invention;

[0025] Figure 2 Schematic diagram of the sand-carrying situation before and after heating of the high-temperature resistant clean fracturing fluid in Example 1 after carrying sand; wherein, (a) is the schematic diagram of the sand-carrying situation before heating, and (b) is the schematic diagram of the sand-carrying situation after heating;

[0026] Figure 3 Schematic diagram of the sand-carrying situation before and after heating of the high-temperature resistant clean fracturing fluid in Example 2 after carrying sand; wherein, (a) is the schematic diagram of the sand-carrying situation before heating, and (b) is the schematic diagram of the sand-carrying situation after heating;

[0027] Figure 4 Schematic diagram of the sand-carrying situation before and after heating of the high-temperature resistant clean fracturing fluid in Example 3 after carrying sand; wherein, (a) is the schematic diagram of the sand-carrying situation before heating, and (b) is the schematic diagram of the sand-carrying situation after heating;

[0028] Figure 5 Schematic diagram of the sand-carrying situation before and after heating of the high-temperature resistant clean fracturing fluid in Example 4 after carrying sand; wherein, (a) is the schematic diagram of the sand-carrying situation before heating, and (b) is the schematic diagram of the sand-carrying situation after heating. Detailed implementation manners

[0029] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, without conflict, the embodiments in the present application and the technical features in the embodiments can be combined with each other. It should be pointed out that unless otherwise specified, all technical and scientific terms used in the present application have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs. The terms "including" or "comprising" and the like used in the present invention disclosure mean that the elements or items appearing before the term cover the elements or items listed after the term and their equivalents, without excluding other elements or items.

[0030] On the one hand, the present invention provides a high-temperature resistant clean fracturing fluid, comprising 2.5 - 4% of a thickening agent, 0.2 - 0.5% of an anti-swelling agent, 0.8 - 2% of an anti-ion auxiliary agent, 0.3 - 0.5% of a temperature-resistant stabilizer, and the balance is water.

[0031] In a specific embodiment, the thickening agent is composed of a high-temperature resistant double quaternary ammonium salt surfactant and erucamide propyl betaine mixed in a mass ratio of 4.5 - 8:2 - 5.5.

[0032] In the above embodiment, the thickening agent is composed of a high-temperature resistant double quaternary ammonium salt surfactant and erucamide propyl betaine. The high-temperature resistant double quaternary ammonium salt surfactant has double cations due to its double quaternary ammonium salt structure, and the two hydrophilic groups enable it to more easily form worm-like micelle structures in water and the micelle structures are more stable. Moreover, the dosage adopted in the present invention enables the worm-like micelles formed by the high-temperature resistant double quaternary ammonium salt surfactant to be intertwined into a network structure (as Figure 1 shown), so that the high-temperature resistant clean fracturing fluid of the present invention has excellent viscoelasticity and temperature and shear resistance. The erucamide propyl betaine is an amphoteric ion surfactant, and its combined use with the high-temperature resistant double quaternary ammonium salt surfactant has a significant thickening effect, which can greatly reduce the dosage of the thickening agent. In addition, the erucamide propyl betaine can also reduce the electrostatic adsorption of the high-temperature resistant double quaternary ammonium salt surfactant, thereby reducing reservoir damage. The high-temperature resistant double quaternary ammonium salt surfactant and erucamide propyl betaine are compounded as the thickening agent, enabling the present invention to only require a thickening agent dosage of 2.5 - 4% to thicken the sand-carrying fluid, which can effectively reduce costs.

[0033] In a specific embodiment, the structural general formula of the high-temperature resistant double quaternary ammonium salt surfactant is:

[0034]

[0035] In the formula: R is C8 - C 16 alkyl.

[0036] In a specific embodiment, the high-temperature resistant double quaternary ammonium salt surfactant shown in formula (I) is obtained through the following steps:

[0037] Mix N-methylethanolamine, dimethyl phthalate, and a solvent, stir evenly, and then let it stand at room temperature for 5 - 6 h to obtain an intermediate product;

[0038] Add bromoalkane to the intermediate product, stir evenly, and then react at 40 - 60 °C for 10 - 12 h to obtain a product;

[0039] Dry the product to obtain the high-temperature resistant double quaternary ammonium salt surfactant.

[0040] It should be noted that the preparation method of the high-temperature resistant bisquaternary ammonium salt surfactant in the above embodiment is only a preferred preparation method of the present invention. Based on the knowledge of the chemical structural formula of the high-temperature resistant bisquaternary ammonium salt surfactant, those skilled in the art can prepare the high-temperature resistant bisquaternary ammonium salt surfactant by using various different agents and preparation methods according to the chemical reaction principle.

[0041] In a specific embodiment, the molar ratio of N-methylethanolamine to dimethyl phthalate is 2 - 2.2:0.8 - 1, the volume ratio of the solvent to N-methylethanolamine and dimethyl phthalate is 3 - 4:1, and the molar ratio of the bromoalkane to dimethyl phthalate is 2 - 2.1:0.9 - 1. Optionally, the solvent is ethanol or acetone.

[0042] In a specific embodiment, the swelling inhibitor is a potassium salt. Optionally, the potassium salt is any one or more of potassium chloride, potassium acetate, and potassium bromide. In this embodiment, the swelling inhibitor uses a potassium salt. The swelling of clay minerals in the formation is mostly caused by the swelling of montmorillonite crystal layers. Because the ionic radius of K + is close to the diameter of the hexagonal ring network between montmorillonite layers, K + can be embedded to inhibit the lattice swelling caused by the charge attraction between montmorillonite layers, thereby achieving the purpose of swelling prevention.

[0043] In a specific embodiment, the counterion assistant is any one or more of sodium toluenesulfonate, sodium salicylate, sodium dodecyl sulfate, sodium citrate, and sodium dioctyl sulfosuccinate. In this embodiment, using organic acid salts as counterion assistants can avoid the influence of high-concentration inorganic salt ions on the wettability of the formation and reduce reservoir damage. It should be noted that the counterion assistant can weaken the repulsion between the cationic polar groups of the high-temperature resistant bisquaternary ammonium salt surfactant through electrostatic interaction, promoting the formation of a tightly structured micelle system. In addition to the organic acid salts preferably used as counterion assistants in this embodiment, other counterion assistants in the prior art that can achieve this purpose can also be applied to the present invention.

[0044] In a specific embodiment, the temperature-resistant stabilizer is any one or more of sodium thiosulfate, sodium dodecyl sulfate, and diethyltoluenediamine. It should be noted that the temperature-resistant stabilizer can improve the stability of the fracturing fluid system at high temperatures, thereby increasing the temperature-resistant range of the fracturing fluid. In addition to the temperature-resistant stabilizers preferably used in this embodiment, other temperature-resistant stabilizers in the prior art that can achieve this purpose can also be applied to the present invention.

[0045] On the other hand, the present invention also provides a preparation method of the high-temperature resistant clean fracturing fluid described in any one of the above, comprising the following steps: adding a thickening agent, an anti-swelling agent, an anti-ion assistant, and a temperature-resistant stabilizer into water in sequence under stirring conditions according to a ratio, and obtaining the high-temperature resistant clean fracturing fluid after thickening.

[0046] In the present invention, the high-temperature resistant clean fracturing fluid can be prepared through the above simple preparation method, the thickening time is about 60 s, the requirements for equipment are low, and continuous mixing and fracturing construction can be realized.

[0047] Example 1

[0048] A high-temperature resistant clean fracturing fluid is prepared through the following steps:

[0049] (1) Add 40 mL of acetone as a solvent into a 100 mL round-bottom flask, then add 5 g of N-methylethanolamine and 6.5 g of dimethyl phthalate, stir evenly, and let it stand at room temperature for 5 h to obtain an intermediate product;

[0050] (2) Place the round-bottom flask in a 45 °C constant temperature water bath, add 13 g of n-octyl bromide dropwise at a stirring speed of 300 r / min, stir evenly, and continue to react in the constant temperature water bath for 11 h to obtain a yellow viscous liquid;

[0051] (3) Dry the yellow viscous liquid at 85 °C to obtain a high-temperature resistant bisquaternary ammonium salt surfactant;

[0052] (4) Take a 1000 mL beaker, measure 480.5 mL of tap water, and start stirring;

[0053] (5) Weigh 12.5 g of a thickening agent (composed of 5.6 g of the high-temperature resistant bisquaternary ammonium salt surfactant prepared in step (3) and 6.9 g of erucamide propyl betaine), add the thickening agent into the stirring tap water, then sequentially weigh and add 1.5 g of an anti-swelling agent (potassium chloride), 4 g of an anti-ion assistant (sodium salicylate), and 1.5 g of a temperature-resistant stabilizer (diethyltoluenediamine), stir for 50 s to obtain a thickened liquid, and stop stirring at this time to obtain the high-temperature resistant clean fracturing fluid.

[0054] Example 2

[0055] A high-temperature resistant clean fracturing fluid is prepared through the following steps:

[0056] (1) Add 60 mL of ethanol as a solvent into a 100 mL round-bottom flask, then add 8 g of N-methylethanolamine and 10 g of dimethyl phthalate, stir evenly, and let it stand at room temperature for 6 h to obtain an intermediate product;

[0057] (2) Place the round-bottom flask in a constant temperature water bath at 50 °C, and dropwise add 21 g of n-octyl bromide at a stirring speed of 300 r / min. After stirring evenly, continue to react in the constant temperature water bath for 11 h to obtain a yellow viscous liquid;

[0058] (3) Dry the yellow viscous liquid at 85 °C to obtain a high-temperature resistant bisquaternary ammonium salt surfactant;

[0059] (4) Take a 1000 mL beaker, measure 476 mL of tap water, and start stirring;

[0060] (5) Weigh 15 g of thickening agent (composed of 9 g of the high-temperature resistant bisquaternary ammonium salt surfactant prepared in step (3) and 6 g of erucic acid amide propyl betaine), add the thickening agent to the stirring tap water, and then successively weigh and add 2 g of anti-swelling agent (potassium acetate), 5 g of counter-ion assistant (sodium dioctyl sulfosuccinate), and 2 g of temperature-resistant stabilizer (diethyltoluenediamine). After stirring for 50 s, a thickened liquid is obtained. At this time, stop stirring to obtain the high-temperature resistant clean fracturing fluid.

[0061] Example 3

[0062] A high-temperature resistant clean fracturing fluid is prepared by the following steps:

[0063] (1) Add 60 mL of acetone as a solvent to a 100 mL round-bottom flask, then add 8 g of N-methylethanolamine and 10 g of dimethyl phthalate. After stirring evenly, let it stand at room temperature for 6 h to obtain an intermediate product;

[0064] (2) Place the round-bottom flask in a constant temperature water bath at 45 °C, and dropwise add 27.7 g of dodecyl bromide at a stirring speed of 300 r / min. After stirring evenly, continue to react in the constant temperature water bath for 12 h to obtain a yellow viscous liquid;

[0065] (3) Dry the yellow viscous liquid at 80 °C to obtain a high-temperature resistant bisquaternary ammonium salt surfactant;

[0066] (4) Take a 1000 mL beaker, measure 468.5 mL of tap water, and start stirring;

[0067] (5) Weigh 19 g of thickening agent (composed of 13.68 g of the high-temperature resistant bisquaternary ammonium salt surfactant prepared in step (3) and 5.32 g of erucic acid amide propyl betaine), add the thickening agent to the stirring tap water, and then successively weigh and add 1.5 g of anti-swelling agent (potassium bromide), 9 g of counter-ion assistant (sodium toluenesulfonate), and 2 g of temperature-resistant stabilizer (sodium thiosulfate). After stirring for 60 s, a thickened liquid is obtained. At this time, stop stirring to obtain the high-temperature resistant clean fracturing fluid.

[0068] Example 4

[0069] A high-temperature resistant clean fracturing fluid is prepared through the following steps:

[0070] (1) Add 70 mL of ethanol as a solvent into a 100 mL round-bottom flask, then add 10 g of N-methylethanolamine and 13 g of dimethyl phthalate, stir evenly, and let it stand for 6 h at room temperature to obtain an intermediate product;

[0071] (2) Place the round-bottom flask in a 55 °C constant temperature water bath, dropwise add 34.5 g of tetradecyl bromide at a stirring speed of 300 r / min, stir evenly, and continue to react in the constant temperature water bath for 12 h to obtain a yellow viscous liquid;

[0072] (3) Dry the yellow viscous liquid at 85 °C to obtain a high-temperature resistant bisquaternary ammonium salt surfactant;

[0073] (4) Take a 1000 mL beaker, measure 467 mL of tap water, and start stirring;

[0074] (5) Weigh 20 g of a thickening agent (composed of 16 g of the high-temperature resistant bisquaternary ammonium salt surfactant prepared in step (3) and 4 g of erucylamidopropyl betaine), add the thickening agent to the stirring tap water, then sequentially weigh and add 1.5 g of an anti-swelling agent (potassium chloride), 9 g of an anti-ion auxiliary agent (sodium citrate), and 2.5 g of a temperature-resistant stabilizer (composed of 0.83 g of sodium dodecyl sulfonate and 1.67 g of diethyltoluenediamine), stir for 60 s to obtain a thickened liquid, and stop stirring at this time to obtain the high-temperature resistant clean fracturing fluid.

[0075] Comparative Example 1

[0076] Differing from Example 4, in step (5) of this comparative example, the 20 g of thickening agent is entirely composed of the high-temperature resistant bisquaternary ammonium salt surfactant prepared in step (3).

[0077] Comparative Example 2

[0078] Differing from Example 4, this comparative example does not include steps (1)-(3), and the 20 g of thickening agent in step (5) of this comparative example is entirely composed of erucylamidopropyl betaine.

[0079] Comparative Example 3

[0080] Differing from Example 4, in step (5) of this comparative example, the 20 g of thickening agent is composed of 16 g of the high-temperature resistant bisquaternary ammonium salt surfactant prepared in step (3) and 4 g of cocamidopropyl betaine mixed together.

[0081] Test Example 1

[0082] Take 50 g of the fracturing fluid of each example and each comparative example. Shear the fracturing fluid of Example 1 at 70 °C for 90 min under 170 S -1 conditions, shear the fracturing fluid of Example 2 at 100 °C for 90 min under 170 S -1 conditions, shear the fracturing fluid of Example 3 at 130 °C for 90 min under 170 S -1 conditions, shear the fracturing fluids of Example 4 and Comparative Examples 1-3 at 160 °C for 90 min under 170 S -1 conditions, and test the viscosities of the fracturing fluids before and after shearing. The test results are shown in Table 1:

[0083] Table 1 Viscosity test results of the fracturing fluids of each example and each comparative example

[0084]

[0085] As can be seen from Table 1, the viscosity of the high-temperature resistant clean fracturing fluid described in the present invention is greater than 50 mPa·s after shearing at different temperatures for 90 min. The high-temperature resistant clean fracturing fluid described in the present invention has good temperature resistance and shear resistance performance.

[0086] When only the high-temperature resistant bisquaternary ammonium salt surfactant is used as the thickening agent without being compounded with erucamide propyl betaine and only erucamide propyl betaine is used without being compounded with the high-temperature resistant bisquaternary ammonium salt surfactant, the viscosity and temperature resistance and shear resistance performance of the prepared fracturing fluid decrease significantly, indicating that the compound use of the high-temperature resistant bisquaternary ammonium salt surfactant and the erucamide propyl betaine described in the present invention can greatly improve the viscosity and temperature resistance and shear resistance performance of the fracturing fluid.

[0087] When the thickening agent is compounded with coconut oil amide propyl betaine and the high-temperature resistant bisquaternary ammonium salt surfactant, the viscosity and temperature resistance and shear resistance performance of the prepared fracturing fluid decrease significantly compared with Example 4 and are very similar to those of Comparative Example 1, indicating that the compounding of coconut oil amide propyl betaine and the high-temperature resistant bisquaternary ammonium salt surfactant has no obvious effect on the viscosity and temperature resistance and shear resistance performance of the fracturing fluid.

[0088] Test Example 2

[0089] Take 50 g of the fracturing fluid of each example, add 5 g of 20 / 40 mesh quartz sand, stir evenly with a stirrer, then add the sand-carrying fracturing fluid into a 100 mL test tube, and then put the test tube into a 90 °C constant temperature water bath and heat for 30 min. The sand-carrying situations of the fracturing fluids before and after heating in each example are respectively as Figures 2 - 5 shown.

[0090] From Figures 2 - 5It can be seen that for the high-temperature resistant clean fracturing fluid in Examples 1-4, when the temperature is 90°C, more than 95% of the proppants do not settle, indicating that the sand suspension performance of the high-temperature resistant clean fracturing fluid is such that the settling time of 95% of the proppants is greater than 30 minutes at 90°C.

[0091] In summary, the main agent dosage of the high-temperature resistant clean fracturing fluid of the present invention is low, the formation damage is low, the applicable reservoir temperature ranges from 70°C to 160°C, and there is no need to add a gel breaker. It can automatically break the gel in environments such as oil, water, and hydrocarbons, with complete gel breaking and no residue, and can meet the needs of fracturing and reconstruction of high-temperature and low-permeability reservoirs. Compared with the prior art, the present invention has made significant progress.

[0092] The above are only representative embodiments of the present invention and do not impose any formal limitations on the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, using the technical content disclosed above to make some modifications or modified embodiments are equivalent embodiments of the present invention. However, as long as the content does not depart from the technical solution of the present invention, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A high-temperature resistant clean fracturing fluid, characterized in that, Comprising, by weight percentage, 2.5 - 4% of thickening agent, 0.2 - 0.5% of anti-swelling agent, 0.8 - 2% of counter-ion assistant, 0.3 - 0.5% of temperature-resistant stabilizer, and the balance being water.

2. The high-temperature resistant clean fracturing fluid according to claim 1, wherein The thickening agent is composed of a high-temperature-resistant bisquaternary ammonium salt surfactant and erucylamidopropyl betaine mixed in a mass ratio of 4.5 - 8:2 - 5.

5.

3. The high-temperature resistant clean fracturing fluid according to claim 2, wherein, The structural general formula of the high-temperature-resistant bisquaternary ammonium salt surfactant is: Wherein: R is C8-C 16 alkyl group.

4. The high-temperature resistant clean fracturing fluid according to claim 3, wherein The high-temperature-resistant bisquaternary ammonium salt surfactant is obtained through the following steps: Mix N-methylethanolamine, dimethyl phthalate, and a solvent, stir evenly, and let stand at room temperature for 5 - 6 h to obtain an intermediate product; Add an alkyl bromide to the intermediate product, stir evenly, and react at 40 - 60 °C for 10 - 12 h to obtain a product; Dry the product to obtain the high-temperature-resistant bisquaternary ammonium salt surfactant.

5. The high-temperature resistant clean fracturing fluid according to claim 4, wherein The molar ratio of N-methylethanolamine to dimethyl phthalate is 2 - 2.2:0.8 - 1, the volume ratio of the solvent to N-methylethanolamine and dimethyl phthalate is 3 - 4:1, and the molar ratio of the alkyl bromide to dimethyl phthalate is 2 - 2.1:0.9 - 1.

6. The high-temperature resistant clean fracturing fluid according to any one of claims 1-5, characterized in that, The anti-swelling agent is a potassium salt.

7. The high-temperature resistant clean fracturing fluid according to claim 5, characterized in that The potassium salt is any one or more of potassium chloride, potassium acetate, and potassium bromide.

8. The high-temperature resistant clean fracturing fluid according to any one of claims 1-5, characterized in that, The counter-ion assistant is any one or more of sodium toluenesulfonate, sodium salicylate, sodium dodecyl sulfate, sodium citrate, and sodium dioctyl sulfosuccinate.

9. The high-temperature resistant clean fracturing fluid according to any one of claims 1-5, characterized in that, The temperature-resistant stabilizer is any one or more of sodium thiosulfate, sodium dodecyl sulfate, and diethyltoluenediamine.

10. The preparation method of the high-temperature resistant clean fracturing fluid according to any one of claims 1-9, characterized in that, Including the following steps: Add the thickening agent, anti-swelling agent, counter-ion assistant, and temperature-resistant stabilizer to water in sequence under stirring conditions according to the ratio, and obtain the high-temperature-resistant clean fracturing fluid after thickening.

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