Dicarboxylic single-tail amphoteric surfactants, cleanup aids for acid fracturing, and methods of making the same

Abstract

The present application relates to fracturing fluid additive preparation technical field, it is a kind of double carboxyl single tail amphoteric surfactant and its preparation method, also include a kind of acidification fracturing cleanup additive and its preparation method, the latter is obtained according to the following method: the required amount of water is added to the required amount of double carboxyl single tail amphoteric surfactant, sodium dodecyl benzene sulfonate and glycosyl nonionic surfactant is stirred uniformly to obtain.The double carboxyl single tail amphoteric surfactant of the present application has the characteristics of simple process, high product yield, biodegradable and safe and reliable, the cleanup additive for acidification fracturing obtained by compounding anionic surfactant and nonionic surfactant using the double carboxyl single tail amphoteric surfactant of the present application as raw material, can effectively reduce the water solution surface interfacial tension, meet the non-fluorocarbon cleanup additive industry use standard.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fracturing fluid additive preparation, and is a double-carboxyl single-tail amphoteric surfactant, a cleanup additive for acid fracturing, and a preparation method thereof. BACKGROUND

[0002] Acid fracturing reconstruction technology is an important measure for efficient development of oil and gas fields, and is a main technical means for realizing unconventional oil and gas resource exploration and development, conventional oil and gas field yield increase and stable production, and improving reservoir reconstruction effect. In the acid fracturing process, the well return fluid is usually quickly discharged to the ground by relying on the formation pressure. When the formation pressure gradually decreases, the return rate is obviously reduced, and the residues in the return fluid are precipitated to cause plugging, resulting in secondary pollution of the formation, thereby seriously affecting the construction efficiency and the acid fracturing reconstruction effect. In order to solve the problem of difficult return of the return fluid after oil acid fracturing, the cleanup additive is a conventional means.

[0003] The cleanup additive is one of the fracturing fluid additives, which can effectively reduce the surface tension and the interfacial tension, reduce the capillary resistance, and improve the return rate and the return rate, thereby reducing the formation damage. At present, many types of cleanup additives are used at home and abroad, but most of them are prepared by compounding fluorocarbon surfactants and other surfactants. The fluorocarbon surfactant has high surface activity, and can reduce the surface tension to 23 mN / m. However, it is expensive, difficult to degrade, and has high biological toxicity. Therefore, it is urgent to develop a green and environmentally friendly cleanup additive system. SUMMARY

[0004] The present application provides a double-carboxyl single-tail amphoteric surfactant, a cleanup additive for acid fracturing, and a preparation method thereof, which overcomes the shortcomings of the prior art, and effectively solves the problems of difficult degradation and high biological toxicity of the existing fluorocarbon surfactant.

[0005] One of the technical solutions of the present application is realized by the following measures: a double-carboxyl single-tail amphoteric surfactant, the structural formula of which is as follows:

[0006]

[0007] In the formula, R is a fatty hydrocarbon group of C12 to C16.

[0008] The following is a further optimization or / and improvement of the above-mentioned one of the technical solutions:

[0009] The above-mentioned double-carboxyl single-tail amphoteric surfactant is obtained by the following method:

[0010] S1, adding N,N-dimethyl-1, 3-propanediamine into a reaction kettle containing anhydrous ethanol, stirring uniformly, reducing the temperature of the reaction kettle by ice water bath, then adding methyl acrylate into the reaction kettle, and reacting at room temperature to obtain a diester intermediate;

[0011] S2, adding a bromoalkane into the reaction kettle containing the diester intermediate, heating to reflux and continuing to react to obtain a diester single-tail surfactant;

[0012] S3, adding sodium hydroxide into the reaction kettle containing the diester single-tail surfactant, adjusting the pH value of the material in the reaction kettle, continuing to react, evaporating and concentrating the reaction product in the reaction kettle after the reaction is completed, adding ethyl acetate into the obtained concentrate to recrystallize, and obtaining a dicarboxylic acid single-tail amphoteric surfactant.

[0013] In the above step S1, the molar ratio of N,N-dimethyl-1, 3-propanediamine to methyl acrylate is 1:2.0 to 2.2.

[0014] In the above step S1, the temperature of the reaction kettle reduced by ice water bath is 0℃ to 5℃, and the reaction time is 22h to 26h.

[0015] In the above step S2, the molar ratio of N,N-dimethyl-1, 3-propanediamine to bromoalkane is 1:1.0 to 1.2.

[0016] In the above step S2, the temperature is heated to 70℃ to 80℃, and the reaction is refluxed for 8h to 24h.

[0017] In the above step S3, the pH value of the material in the reaction kettle is adjusted to 6.8 to 7.2, and the reaction is continued for 2h to 6h.

[0018] The second technical scheme of the present application is realized by the following measures: a preparation method of a dicarboxylic acid single-tail amphoteric surfactant, which is carried out according to the following method:

[0019] S1, adding N,N-dimethyl-1, 3-propanediamine into a reaction kettle containing anhydrous ethanol, stirring uniformly, reducing the temperature of the reaction kettle by ice water bath, then adding methyl acrylate into the reaction kettle, and reacting at room temperature to obtain a diester intermediate;

[0020] S2, adding a bromoalkane into the reaction kettle containing the diester intermediate, heating to reflux and continuing to react to obtain a diester single-tail surfactant;

[0021] S3, adding sodium hydroxide into the reaction kettle containing the diester single-tail surfactant, adjusting the pH value of the material in the reaction kettle, continuing to react, evaporating and concentrating the reaction product in the reaction kettle after the reaction is completed, adding ethyl acetate into the obtained concentrate to recrystallize, and obtaining a dicarboxylic acid single-tail amphoteric surfactant.

[0022] The following is a further optimization or / and improvement of the above-mentioned technical scheme two:

[0023] In the above step S1, the molar ratio of N,N-dimethyl-1,3-propanediamine to methyl acrylate is 1:2.0 to 2.2.

[0024] In the above step S1, the ice water bath reduces the temperature of the reaction kettle to 0℃ to 5℃, and the reaction time is 22h to 26h.

[0025] In the above step S2, the molar ratio of N,N-dimethyl-1,3-propanediamine to brominated alkane is 1:1.0 to 1.2.

[0026] In the above step S2, the temperature is raised to 70℃ to 80℃, and the reflux reaction is 8h to 24h.

[0027] In the above step S3, the pH value of the material in the reaction kettle is adjusted to 6.8 to 7.2, and the reaction is continued for 2h to 6h.

[0028] The third technical scheme of the present application is realized by the following measures: an acidizing fracturing cleanup aid, the raw materials include 8.0% to 9.5% of double-carboxyl single-tail amphoteric surfactant, 0.5% to 1.0% of sodium dodecyl benzene sulfonate, 0.25% to 0.5% of sugar-based nonionic surfactant, and the balance of water, and the acidizing fracturing cleanup aid is obtained by the following method: adding the required amount of double-carboxyl single-tail amphoteric surfactant, sodium dodecyl benzene sulfonate and sugar-based nonionic surfactant into the required amount of water and stirring uniformly.

[0029] The following is a further optimization or / and improvement of the above-mentioned technical scheme three:

[0030] The above sugar-based anionic surfactant is N-alkyl glucose amide.

[0031] The fourth technical scheme of the present application is realized by the following measures: a preparation method of an acidizing fracturing cleanup aid, the raw materials include 8.0% to 9.5% of double-carboxyl single-tail amphoteric surfactant, 0.5% to 1.0% of sodium dodecyl benzene sulfonate, 0.25% to 0.5% of sugar-based nonionic surfactant, and the balance of water, and the preparation method is as follows: adding the required amount of double-carboxyl single-tail amphoteric surfactant, sodium dodecyl benzene sulfonate and sugar-based nonionic surfactant into the required amount of water and stirring uniformly to obtain the acidizing fracturing cleanup aid.

[0032] The double-carboxyl single-tail amphoteric surfactant has the characteristics of simple process, high product yield, biodegradability and safety and reliability, the acidizing fracturing cleanup additive prepared by compounding anionic surfactants and nonionic surfactants by using the double-carboxyl single-tail amphoteric surfactant as a raw material can effectively reduce the water solution interfacial tension, meet the non-fluorocarbon cleanup additive industry use standard, and significantly reduce the total amount of surfactants in the cleanup additive, and reduce the use cost. DETAILED DESCRIPTION

[0033] The present application is not limited by the following examples, and the specific implementation can be determined according to the technical scheme of the present application and the actual situation. The various chemical reagents and chemical supplies mentioned in the present application are well-known and commonly used chemical reagents and chemical supplies in the prior art unless otherwise specified; the percentages in the present application are mass percentages unless otherwise specified; the solution in the present application is a water solution with water as a solvent unless otherwise specified, for example, a hydrochloric acid solution is a hydrochloric acid water solution; the normal temperature and room temperature in the present application generally refer to a temperature of 15 to 25 DEG C, and is generally defined as 25 DEG C.

[0034] The present application will be further described below in combination with examples:

[0035] Example 1: The double-carboxyl single-tail amphoteric surfactant has the following structural formula:

[0036]

[0037] In the formula, R is a C12 to C16 aliphatic hydrocarbon group.

[0038] Example 2: As an optimization of the above example, the double-carboxyl single-tail amphoteric surfactant is obtained by the following method:

[0039] S1, N,N-dimethyl-1,3-propanediamine is added to a reaction kettle containing anhydrous ethanol, stirred uniformly, the temperature of the reaction kettle is lowered by ice water bath, then methyl acrylate is added to the reaction kettle, and the reaction is carried out at room temperature to obtain a double ester intermediate;

[0040] S2, bromoalkane is added to the reaction kettle containing the double ester intermediate, the reaction is continued by heating and refluxing to obtain a double ester single-tail surfactant;

[0041] S3, sodium hydroxide is added to the reaction kettle containing the double ester single-tail surfactant, the pH value of the material in the reaction kettle is adjusted, the reaction is continued, after the reaction is completed, the reaction product in the reaction kettle is evaporated and concentrated, ethyl acetate is added to the obtained concentrate for recrystallization to obtain the double-carboxyl single-tail amphoteric surfactant.

[0042] The chemical equation of the above-mentioned double-carboxyl single-tail amphoteric surfactant preparation method is as follows:

[0043] Step S1: Preparation of the diester intermediate:

[0044]

[0045] Step S2: Preparation of the diester mono-tail surfactant:

[0046]

[0047] Step S3: Preparation of the di-carboxylic mono-tail zwitterionic surfactant:

[0048]

[0049] Example 3: As an optimization of the above examples, in Step S1, the molar ratio of N,N-dimethyl-1,3-propanediamine to methyl acrylate is 1:2.0 to 2.2.

[0050] Example 4: As an optimization of the above examples, in Step S1, the ice water bath reduces the temperature of the reaction kettle to 0°C to 5°C, and the reaction time is 22h to 26h.

[0051] Example 5: As an optimization of the above examples, in Step S2, the molar ratio of N,N-dimethyl-1,3-propanediamine to bromoalkane is 1:1.0 to 1.2.

[0052] Example 6: As an optimization of the above examples, in Step S2, the temperature is raised to 70°C to 80°C, and the reaction is refluxed for 8h to 24h.

[0053] Example 7: As an optimization of the above examples, in Step S3, the pH value of the material in the reaction kettle is adjusted to 6.8 to 7.2, and the reaction is continued for 2h to 6h.

[0054] Example 8: The cleanup aid for acidizing fracturing obtained by using the di-carboxylic mono-tail zwitterionic surfactant described in the above examples as one of the raw materials, the raw materials include 8.0% to 9.5% di-carboxylic mono-tail zwitterionic surfactant, 0.5% to 1.0% sodium dodecyl benzene sulfonate, 0.25% to 0.5% sugar-based non-ionic surfactant, and the balance of water, by weight percentage, is obtained by the following method: adding the required amount of di-carboxylic mono-tail zwitterionic surfactant, sodium dodecyl benzene sulfonate and sugar-based non-ionic surfactant to the required amount of water and stirring uniformly to obtain the cleanup aid for acidizing fracturing.

[0055] Example 9: As an optimization of the above examples, the sugar-based anionic surfactant is N-alkyl glucose amide, and its molecular structure formula is:

[0056]

[0057] Wherein, R is an aliphatic hydrocarbon group from C12 to C16.

[0058] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0059] (1) The dicarboxylated monotail amphoteric surfactant of the present invention is prepared by a "one-pot method". The method is simple, the product yield is high, it is safe and reliable, and the product is green and biodegradable.

[0060] (2) The dicarboxylated mono-tailed amphoteric surfactant of the present invention has good composite synergistic effect with anionic surfactant and nonionic surfactant, which can effectively reduce the interfacial tension of aqueous solution and significantly reduce the total amount of surfactant in the drainage aid, thereby reducing the cost of use.

[0061] Example 10:

[0062] This dicarboxylated mono-tailed amphoteric surfactant was obtained by the following method:

[0063] S1, N,N-dimethyl-1,3-propanediamine was added to a reaction vessel containing anhydrous ethanol and stirred until homogeneous. The temperature of the reaction vessel was lowered to 0°C using an ice-water bath. Methyl acrylate was then added to the reaction vessel, and the reaction was carried out at room temperature for 22 hours to obtain a diester intermediate. The molar ratio of N,N-dimethyl-1,3-propanediamine to methyl acrylate was 1:2.0.

[0064] S2, add hexadecane bromide to a reactor containing a diester intermediate, heat to 70°C, reflux and continue the reaction for 8 hours to obtain a diester single-tailed surfactant; wherein, the molar ratio of N,N-dimethyl-1,3-propanediamine to hexadecane bromide is 1:1.0;

[0065] S3. Sodium hydroxide was added to the reactor containing the diester mono-tailed surfactant to adjust the pH of the material in the reactor to 6.8. The reaction was continued for 2 hours. After the reaction was completed, the reaction product in the reactor was evaporated and concentrated, the solvent was recovered, and ethyl acetate was added to the obtained concentrate for recrystallization to obtain the dicarboxylic acid mono-tailed amphoteric surfactant.

[0066] This acid fracturing flow aid is obtained according to the following method:

[0067] The raw materials, by weight percentage, comprise 8.0% dicarboxylated mono-tailed amphoteric surfactant, 0.5% sodium dodecylbenzenesulfonate, and 0.25% N-hexadecylglucamide, with the balance being water. The raw materials are obtained by adding the required amounts of dicarboxylated mono-tailed amphoteric surfactant, sodium dodecylbenzenesulfonate, and N-hexadecylglucamide to the required amount of water and stirring until homogeneous, thus obtaining an acid fracturing aid.

[0068] Example 11:

[0069] This dicarboxylated mono-tailed amphoteric surfactant was obtained by the following method:

[0070] S1, N,N-dimethyl-1,3-propanediamine was added to a reaction vessel containing anhydrous ethanol and stirred until homogeneous. The temperature of the reaction vessel was lowered to 5°C using an ice-water bath. Then, methyl acrylate was added to the reaction vessel and the reaction was carried out at room temperature for 26 hours to obtain a diester intermediate. The molar ratio of N,N-dimethyl-1,3-propanediamine to methyl acrylate was 1:2.2.

[0071] S2, add bromotetradecane to a reactor containing a diester intermediate, heat to 80°C, reflux and continue the reaction for 24 hours to obtain a diester single-tailed surfactant; wherein, the molar ratio of N,N-dimethyl-1,3-propanediamine to bromotetradecane is 1:1.2.

[0072] S3. Sodium hydroxide was added to the reactor containing the diester mono-tailed surfactant to adjust the pH of the material in the reactor to 7.2. The reaction was continued for 6 hours. After the reaction was completed, the reaction product in the reactor was evaporated and concentrated, the solvent was recovered, and ethyl acetate was added to the obtained concentrate for recrystallization to obtain the dicarboxylic acid mono-tailed amphoteric surfactant.

[0073] This acid fracturing flow aid is obtained according to the following method:

[0074] The raw materials, by weight percentage, comprise 9.5% dicarboxylated mono-tailed amphoteric surfactant, 1.0% sodium dodecylbenzenesulfonate, and 0.5% N-tetradecylglucamide, with the balance being water. The raw materials are obtained by adding the required amounts of dicarboxylated mono-tailed amphoteric surfactant, sodium dodecylbenzenesulfonate, and N-tetradecylglucamide to the required amount of water and stirring until homogeneous, thus obtaining an acid fracturing aid.

[0075] Example 12:

[0076] This dicarboxylated mono-tailed amphoteric surfactant was obtained by the following method:

[0077] S1, N,N-dimethyl-1,3-propanediamine was added to a reaction vessel containing anhydrous ethanol and stirred until homogeneous. The temperature of the reaction vessel was lowered to 2°C using an ice-water bath. Then, methyl acrylate was added to the reaction vessel and the reaction was carried out at room temperature for 24 hours to obtain a diester intermediate. The molar ratio of N,N-dimethyl-1,3-propanediamine to methyl acrylate was 1:2.1.

[0078] S2, add hexadecane bromide to a reaction vessel containing a diester intermediate, heat to 75°C, reflux and continue the reaction for 18 hours to obtain a diester single-tailed surfactant; wherein, the molar ratio of N,N-dimethyl-1,3-propanediamine to hexadecane bromide is 1:1.1;

[0079] S3. Sodium hydroxide was added to the reactor containing the diester mono-tailed surfactant to adjust the pH of the material in the reactor to 7.0. The reaction was continued for 4 hours. After the reaction was completed, the reaction product in the reactor was evaporated and concentrated, the solvent was recovered, and ethyl acetate was added to the obtained concentrate for recrystallization to obtain the dicarboxylic acid mono-tailed amphoteric surfactant.

[0080] This acid fracturing flow aid is obtained according to the following method:

[0081] The raw materials, by weight percentage, comprise 9.0% dicarboxylated mono-tailed amphoteric surfactant, 0.8% sodium dodecylbenzenesulfonate, and 0.4% N-hexadecylglucamide, with the balance being water. The raw materials are obtained by adding the required amounts of dicarboxylated mono-tailed amphoteric surfactant, sodium dodecylbenzenesulfonate, and N-hexadecylglucamide to the required amount of water and stirring until homogeneous, thus obtaining an acid fracturing aid.

[0082] Example 13:

[0083] Preparation of this dicarboxylated mono-tailed amphoteric surfactant:

[0084] S1, 0.1 mol of N,N-dimethyl-1,3-propanediamine was dissolved in 100 mL of anhydrous ethanol, stirred until homogeneous, and the temperature was lowered by 2 °C in an ice-water bath. 0.2 mol of methyl acrylate was slowly added dropwise. After the addition was complete, the reaction continued for 24 h to obtain the diester intermediate.

[0085] S2, 0.1 mol of hexadecane bromide was added to the diester intermediate, stirred until homogeneous, heated to 80℃, and refluxed for 8 h to obtain a diester mono-tailed surfactant.

[0086] S3. A 20% NaOH solution was slowly added dropwise to the diester mono-tailed surfactant to adjust the pH to 7.0. The reaction was continued for 2 hours. The mixture was then rotary evaporated to a small volume and recrystallized from ethyl acetate to obtain a viscous liquid dicarboxylic mono-tailed amphoteric surfactant with a yield of 93.6%.

[0087] Preparation of the flow-out aid for acid fracturing:

[0088] Weigh 9.0 parts of dicarboxylated mono-tailed amphoteric surfactant, 0.5 parts of sodium dodecylbenzenesulfonate, 0.25 parts of N-hexadecylglucamide and 90.25 parts of water, stir at room temperature and dissolve evenly to obtain an acid fracturing aid.

[0089] The acid fracturing pumping aid prepared in Example 13 of this invention was subjected to performance testing. The surface tension of the acid fracturing pumping aid with a concentration of 0.3% was 23.281 mN / m and the interfacial tension was 0.109 mN / m, which meets the industry standards for non-fluorocarbon pumping aids.

[0090] Example 14:

[0091] The preparation of this dicarboxylated mono-tailed amphoteric surfactant is the same as in Example 13;

[0092] Preparation of the flow-out aid for acid fracturing:

[0093] Weigh 9.0 parts of dicarboxylated mono-tailed amphoteric surfactant, 0.5 parts of sodium dodecylbenzenesulfonate, 0.5 parts of N-hexadecylglucamide and 90.0 parts of water, stir at room temperature and dissolve evenly to obtain an acid fracturing aid.

[0094] The acid fracturing pumping aid prepared in Example 14 of this invention was subjected to performance testing. The surface tension of the acid fracturing pumping aid with a concentration of 0.3% was 24.058 mN / m and the interfacial tension was 0.085 mN / m, which meets the industry standards for non-fluorocarbon pumping aids.

[0095] Example 15:

[0096] Preparation of this dicarboxylated mono-tailed amphoteric surfactant:

[0097] S1, 0.1 mol of N,N-dimethyl-1,3-propanediamine was dissolved in 100 mL of anhydrous ethanol, stirred until homogeneous, and the temperature was lowered by 2 °C in an ice-water bath. 0.22 mol of methyl acrylate was slowly added dropwise. After the addition was complete, the reaction continued for 24 h to obtain the diester intermediate.

[0098] S2, 0.11 mol of bromotetradecane was added to the diester intermediate, stirred until homogeneous, heated to 80℃, and refluxed for 12 h to obtain a diester single-tailed surfactant.

[0099] S3. A 20% NaOH solution was slowly added dropwise to the diester mono-tailed surfactant to adjust the pH to 7.0. The reaction was continued for 2 hours. The mixture was then rotary evaporated to a small volume and recrystallized from ethyl acetate to obtain a viscous liquid dicarboxylic mono-tailed amphoteric surfactant with a yield of 94.7%.

[0100] Preparation of the flow-out aid for acid fracturing:

[0101] Weigh 9.0 parts of dicarboxylated mono-tailed amphoteric surfactant, 0.5 parts of sodium dodecylbenzenesulfonate, 0.25 parts of N-tetradecylglucamide and 90.25 parts of water, stir at room temperature and dissolve evenly to obtain an acid fracturing aid.

[0102] The acid fracturing pumping aid prepared in Example 15 of this invention was subjected to performance testing. The surface tension of the acid fracturing pumping aid with a concentration of 0.3% was 22.605 mN / m and the interfacial tension was 0.009 mN / m, which meets the industry standards for non-fluorocarbon pumping aids.

[0103] Example 16:

[0104] The preparation of this dicarboxylated mono-tailed amphoteric surfactant is the same as in Example 15;

[0105] Preparation of the flow-out aid for acid fracturing:

[0106] Weigh 8.5 parts of dicarboxylated mono-tailed amphoteric surfactant, 1.0 part of sodium dodecylbenzenesulfonate, 0.5 parts of N-tetradecylglucamide and 90.0 parts of water, stir at room temperature and dissolve evenly to obtain an acid fracturing aid.

[0107] The acid fracturing pumping aid prepared in Example 16 of this invention was subjected to performance testing. The surface tension of the acid fracturing pumping aid with a concentration of 0.3% was 23.037 mN / m and the interfacial tension was 0.161 mN / m, which meets the industry standards for non-fluorocarbon pumping aids.

[0108] In summary, the dicarboxylated single-tailed amphoteric surfactant of this invention has the characteristics of simple process, high product yield, biodegradability and safety. The acid fracturing pumping aid obtained by using the dicarboxylated single-tailed amphoteric surfactant of this invention as raw material and compounding anionic surfactant and nonionic surfactant can effectively reduce the interfacial tension of aqueous solution, meet the industry standards for non-fluorocarbon pumping aids, and significantly reduce the total amount of surfactant in the pumping aid, thereby reducing the cost of use.

[0109] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A dicarboxylated single-tailed amphoteric surfactant, characterized in that... The structural formula is as follows: Wherein, R is an aliphatic hydrocarbon group from C12 to C16.

2. A method for preparing a dicarboxylated mono-tailed amphoteric surfactant according to claim 1, characterized in that... Perform it as follows: S1, N,N-dimethyl-1,3-propanediamine is added to a reaction vessel containing anhydrous ethanol, stirred until homogeneous, and the temperature of the reaction vessel is lowered by an ice-water bath. Then methyl acrylate is added to the reaction vessel, and the reaction occurs at room temperature to obtain a diester intermediate. S2, add bromoalkane to a reaction vessel containing diester intermediate, heat and reflux to continue the reaction, and obtain diester mono-tailed surfactant. S3. Sodium hydroxide is added to the reactor containing diester mono-tailed surfactant to adjust the pH value of the material in the reactor and continue the reaction. After the reaction is completed, the reaction product in the reactor is evaporated and concentrated. Ethyl acetate is added to the obtained concentrate for recrystallization to obtain dicarboxylic acid mono-tailed amphoteric surfactant.

3. The method for preparing the dicarboxylated mono-tailed amphoteric surfactant according to claim 2, characterized in that... In step S1, the molar ratio of N,N-dimethyl-1,3-propanediamine to methyl acrylate is 1:2.0 to 2.2; or / and, in step S1, the temperature of the reactor is lowered by an ice-water bath from 0°C to 5°C, and the reaction time is 22h to 26h.

4. The method for preparing a dicarboxylated mono-tailed amphoteric surfactant according to claim 2 or 3, characterized in that... In step S2, the molar ratio of N,N-dimethyl-1,3-propanediamine to bromoalkane is 1:1.0 to 1.2; or / and, in step S2, the temperature is raised to 70°C to 80°C and refluxed for 8 to 24 hours.

5. The method for preparing a dicarboxylated mono-tailed amphoteric surfactant according to claim 2 or 3, characterized in that... In step S3, the pH value of the material in the reactor is adjusted to 6.8 to 7.2, and the reaction continues for 2 to 6 hours.

6. The method for preparing the dicarboxylated mono-tailed amphoteric surfactant according to claim 4, characterized in that... In step S3, the pH value of the material in the reactor is adjusted to 6.8 to 7.2, and the reaction continues for 2 to 6 hours.

7. A flow aid for acid fracturing prepared using the dicarboxylated mono-tailed amphoteric surfactant as one of the raw materials according to any one of claims 1 to 6, characterized in that... The raw materials, by weight percentage, include 8.0% to 9.5% dicarboxylated mono-tailed amphoteric surfactant, 0.5% to 1.0% sodium dodecylbenzenesulfonate, 0.25% to 0.5% glycosyl nonionic surfactant, and the balance being water.

8. The flow aid for acid fracturing according to claim 7, characterized in that... The glycosyl anionic surfactant is N-alkylglucamide.

9. A method for preparing an acid fracturing flow aid according to claim 7 or 8, comprising the following steps: adding a required amount of dicarboxylated mono-tailed amphoteric surfactant, sodium dodecylbenzenesulfonate, and glycosyl nonionic surfactant to a required amount of water and stirring until homogeneous to obtain the acid fracturing flow aid.

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