Monoamine-polycarboxyl-ampholytic viscoelastic surfactant and preparation method and application thereof

Abstract

The invention discloses a monoamino polycarboxyl amphoteric viscoelastic surfactant, the structural formula of which is: A method for preparing a monoamino polycarboxyl amphoteric viscoelastic surfactant, comprising the following steps: (1) respectively adding alkenyl succinic anhydride, toluene and N,N-dimethylformamide, heating and stirring to obtain a mixed solution; (2) slowly adding triethanolamine to the mixed solution, stirring and heating to obtain a reaction solution; (3) adding chloroacetic acid to the reaction solution, and reacting to obtain a reaction solution; (4) evaporating the reaction solution to obtain a solid crude product; (5) filtering the solid crude product, washing for multiple times, and vacuum drying to obtain a monoamino polycarboxyl amphoteric viscoelastic surfactant. Application of the monoamino polycarboxyl amphoteric viscoelastic surfactant as an oil displacement agent. Application of the monoamino polycarboxyl amphoteric viscoelastic surfactant as a fracturing fluid.

Description

Technical Field

[0001] The invention belongs to the field of surfactants, and in particular relates to a monoamine-polycarboxyl-amphoteric viscoelastic surfactant and a preparation method and application thereof. Background Art

[0002] Surfactant refers to an amphiphilic compound that contains fixed non-polar lipophilic groups and polar hydrophilic groups in its molecular structure. Adding a small amount to a solution can significantly reduce the surface tension of the solution and effectively change the physical and chemical properties of the interface.

[0003] Viscoelastic surfactants are a new type of surfactant that can easily form unique worm-like micelles in water, making their aqueous solutions have excellent viscoelasticity. Viscoelastic surfactants are composed of amphiphilic molecules and have unique physical and chemical properties under formation conditions. They are widely used in the field of oil and gas reservoir production enhancement. Viscoelastic surfactants are dispersed in the solution and form an interface between the originally immiscible liquids, which promotes more contact between the two systems until they mix. The final solution has both viscous and elastic properties.

[0004] However, it is difficult to show the surface tension reduction property of conventional surfactants and the viscoelasticity of viscoelastic surfactants in the same product. Therefore, it is necessary to add conventional surfactants and viscoelastic surfactants separately when using them. This operation has the following disadvantages: there are many types of products to add, which increases the complexity of construction. Conventional surfactants may also destroy the worm-like aggregation of viscoelastic surfactants. When using them, the compatibility between different surfactants must also be considered, resulting in additional risks of use. Summary of the invention

[0005] Purpose of the invention: In view of the deficiencies of the above-mentioned prior art, the present invention provides a monoamine-polycarboxyl amphoteric viscoelastic surfactant and a preparation method and application thereof. The monoamine-polycarboxyl amphoteric viscoelastic surfactant disclosed in the present invention has the dual functions of increasing the viscosity of the injected water and reducing the viscosity by emulsification. When applied to the field of heavy oil cold production, it not only has the effect of improving the oil washing efficiency as a surfactant, but also has the effect of controlling the fluidity and improving the sweep coefficient as a polymer solution. It is an ideal oil displacement medium. In addition, when used as a fracturing fluid, it also has the characteristics of low system viscosity and can effectively reduce construction friction; it is easily soluble in brine and can automatically break the gel after the construction work is completed; since chemical agents such as polymer solid phase, cross-linking agent and gel breaker are not introduced, the possibility of secondary damage to the reservoir by residues is reduced.

[0006] Technical solution: Monoamine-polycarboxyl-ampholytic viscoelastic surfactant, the structural formula of which is:

[0007] in:

[0008] R1 is one of chain hexyl, heptyl, octyl, nonyl, and decyl;

[0009] R2 is one of chain hexyl, heptyl, octyl, nonyl and decyl.

[0010] Further, R1 is a chain octyl group, preferably a straight chain octyl group;

[0011] R2 is a chain octyl group, preferably a straight-chain octyl group.

[0012] A method for preparing a monoamine-polycarboxyl-amphoteric viscoelastic surfactant comprises the following steps:

[0013] (1) Add alkenyl succinic anhydride, toluene and N,N-dimethylformamide to a reaction vessel, heat to 40-50° C., and stir to obtain a mixed solution, wherein:

[0014] The volume ratio of alkenyl succinic anhydride, toluene and N,N-dimethylformamide is (8-12):(70-90):(3-5);

[0015] (2) Slowly add triethanolamine to the mixed solution obtained in step (1), stir evenly, heat to 60-80° C., react for 4-6 hours, and obtain a reaction solution, wherein:

[0016] The molar ratio of the triethanolamine to the alkenyl succinic anhydride is 1:(3-3.5);

[0017] (3) Add chloroacetic acid to the reaction solution obtained in step (2), and then react at 50 to 70° C. for 4 to 6 hours to obtain a reaction solution, wherein:

[0018] The molar ratio of chloroacetic acid to triethanolamine is (1-1.1):1;

[0019] (4) evaporating the reaction solution obtained in step (3) to dryness to obtain a solid crude product;

[0020] (5) The solid crude product obtained in step (4) is filtered, washed multiple times, and vacuum dried to obtain a monoamine-polycarboxyl-ampholytic viscoelastic surfactant.

[0021] Furthermore, the reaction vessel in step (1) is a reaction vessel equipped with a thermometer, an electric stirrer and a condenser, preferably a three-necked flask.

[0022] Furthermore, the volume ratio of alkenyl succinic anhydride, toluene and N,N-dimethylformamide in step (1) is 10:80:4.

[0023] Furthermore, the molar ratio of triethanolamine to alkenyl succinic anhydride added in step (2) is 1:3.

[0024] Furthermore, the molar ratio of chloroacetic acid to triethanolamine added in step (3) is 1.05:1.

[0025] Furthermore, in step (4), the reaction solution is evaporated to dryness by a rotary evaporator, and the vacuum degree of the rotary evaporator in step (4) is 8 to 10 mmHg.

[0026] Furthermore, in step (4), the temperature of the rotary evaporator during evaporation is controlled at 70-100°C.

[0027] Furthermore, the temperature of vacuum drying in step (5) is controlled at 80-100°C.

[0028] Furthermore, the vacuum drying time in step (5) is controlled within 5 to 8 hours.

[0029] The above monoamine-polycarboxyl-amphoteric viscoelastic surfactant is used as an oil displacement agent.

[0030] The above monoamine-polycarboxyl-ampholytic viscoelastic surfactant is used as a fracturing fluid.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] 1. The reaction raw materials have high reactivity, the reaction conditions are mild, and the operation is simple and easy;

[0033] 2. This surfactant has good surface activity not only under acidic conditions, but also under alkaline conditions.

[0034] 3. The surfactant aqueous solution has both low surface tension and the ability to form viscoelastic hydrogels, which can reduce the types of surfactants added when used. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the H-NMR spectrum of the monoamine-polycarboxyl-ampholytic viscoelastic surfactant in Example 3;

[0036] Figure 2 The surface tension diagram of the monoamine-polycarboxyl-ampholytic viscoelastic surfactant in Example 3;

[0037] Figure 3 This is the viscosity diagram of the monoamine-polycarboxyl-ampholytic viscoelastic surfactant in Example 3. DETAILED DESCRIPTION

[0038] The specific implementation methods of the present invention are described in detail below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. 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.

[0039] The present invention discloses a method for rapidly preparing a monoamine-polycarboxyl-ampholytic viscoelastic surfactant, wherein the surfactant has the following structural formula:

[0040]

[0041] R1 is one of chain hexyl, heptyl, octyl, nonyl, and decyl;

[0042] R2 is one of chain hexyl, heptyl, octyl, nonyl and decyl.

[0043] Further, R1 is a chain octyl group, preferably a straight chain octyl group;

[0044] R2 is a chain octyl group, preferably a straight-chain octyl group.

[0045] A method for preparing a monoamine-polycarboxyl-amphoteric viscoelastic surfactant comprises the following steps:

[0046] (1) Add alkenyl succinic anhydride, toluene and N,N-dimethylformamide to a reaction vessel, heat to 40-50° C., and stir to obtain a mixed solution, wherein:

[0047] The volume ratio of alkenyl succinic anhydride, toluene and N,N-dimethylformamide is (8-12):(70-90):(3-5);

[0048] (2) Slowly add triethanolamine to the mixed solution obtained in step (1), stir evenly, heat to 60-80° C., react for 4-6 hours, and obtain a reaction solution, wherein:

[0049] The molar ratio of the triethanolamine to the alkenyl succinic anhydride is 1:(3-3.5);

[0050] (3) Add chloroacetic acid to the reaction solution obtained in step (2), and then react at 50 to 70° C. for 4 to 6 hours to obtain a reaction solution, wherein:

[0051] The molar ratio of chloroacetic acid to triethanolamine is (1-1.1):1;

[0052] (4) evaporating the reaction solution obtained in step (3) to dryness to obtain a solid crude product;

[0053] (5) The solid crude product obtained in step (4) is filtered, washed multiple times (generally 3-5 times), and vacuum dried to obtain a monoamine-polycarboxyl-ampholytic viscoelastic surfactant.

[0054] The preparation path is as follows:

[0055]

[0056] The present invention will be further described below with reference to specific embodiments and accompanying drawings:

[0057] Example 1

[0058] A method for preparing a monoamine-polycarboxyl-amphoteric viscoelastic surfactant comprises the following steps:

[0059] In a three-necked flask equipped with a thermometer, an electric stirrer and a condenser, add 10 ml of alkenyl succinic anhydride (R1 and R2 of ASA are straight-chain hexyl groups), 80 ml of toluene and 4 ml of dimethylformamide (DMF) as a mixed solvent, and stir and dissolve at 50°C;

[0060] Slowly add 2.4 g of triethanolamine into the dissolved three-necked flask, stir and heat to 70°C for 6 hours;

[0061] After the reaction is completed, 0.84 g of chloroacetic acid is added and the reaction is continued at 65°C for 5 h;

[0062] After the reaction was completed, the product was evaporated to dryness using a rotary evaporator at a vacuum degree of 9 mmHg and a temperature of 80°C to obtain a solid crude product;

[0063] The crude product was filtered, washed 5 times, and vacuum dried at 90°C for 6 hours to obtain a monoamine-polycarboxyl-amphoteric viscoelastic surfactant.

[0064] Example 2

[0065] A method for preparing a monoamine-polycarboxyl-amphoteric viscoelastic surfactant comprises the following steps:

[0066] Add 10 ml of alkenyl succinic anhydride (R1 and R2 of ASA are straight-chain heptyl) and a mixed solvent of 80 ml of toluene and 4 ml of dimethylformamide (DMF) into a three-necked flask equipped with a thermometer, an electric stirrer and a condenser, and stir and dissolve at 45°C;

[0067] Slowly add 2.4 g of triethanolamine solution into the dissolved three-necked flask, stir and heat to 75°C for 5 h;

[0068] After the reaction is completed, 0.77 g of chloroacetic acid is added and the reaction is continued at 65°C for 5 h;

[0069] After the reaction was completed, the product was evaporated to dryness using a rotary evaporator at a vacuum degree of 9 mmHg and a temperature of 80°C to obtain a solid crude product;

[0070] The crude product was filtered, washed three times, and vacuum dried at 85°C for 7 hours to obtain a monoamino-polycarboxyl-amphoteric viscoelastic surfactant.

[0071] Example 3

[0072] A method for preparing a monoamine-polycarboxyl-amphoteric viscoelastic surfactant comprises the following steps:

[0073] Add 10 ml of alkenyl succinic anhydride (R1 and R2 of ASA are straight-chain octyl groups), 80 ml of toluene and 4 ml of dimethylformamide (DMF) into a three-necked flask equipped with a thermometer, an electric stirrer and a condenser, and stir and dissolve at 45°C;

[0074] Slowly add 2.4 g of triethanolamine solution into the dissolved three-necked flask, stir and heat to 75°C for 6 hours;

[0075] After the reaction is completed, 0.71 g of chloroacetic acid is added and the reaction is continued at 65°C for 5 h;

[0076] After the reaction was completed, the product was evaporated to dryness using a rotary evaporator at a vacuum degree of 9 mmHg and a temperature of 80°C to obtain a solid crude product;

[0077] The crude product was filtered, washed 5 times, and vacuum dried at 85°C for 7 hours to obtain a monoamino-polycarboxyl-amphoteric viscoelastic surfactant.

[0078] Figure 1 This is the H-NMR spectrum of the monoamine-polycarboxyl-amphoteric viscoelastic surfactant in Example 3.

[0079] 1H NMR (300MHz, DMSO): δ, 13.51 (s, 3H), 13.03 (s, 1H), 5.42~5.34 (m, 3H), 3.63 (m, 6H), 3.3 3~3.30 (t, 8H), 2.63~2.38 (m, 12H), 1.94 (s, 12H), 1.33~1.26 (s, 72H), 0.88 (s, 18H)ppm.

[0080] It can be seen from the figure that the present invention successfully prepared a monoamine-polycarboxyl-ampholytic viscoelastic surfactant with a target structure.

[0081] In order to characterize the effect of the synthesized monoamine-polycarboxyl amphoteric and viscoelastic surfactant, the surface tension of the synthesized monoamine-polycarboxyl amphoteric and viscoelastic surfactant in Example 3 was tested. The results are as follows: Figure 2 shown.

[0082] In order to characterize the effect of the synthesized monoamine-polycarboxyl amphoteric viscoelastic surfactant, the viscosity of the synthesized monoamine-polycarboxyl amphoteric viscoelastic surfactant in Example 3 was tested at 40°C. The results are as follows: Figure 3 shown.

[0083] Example 4

[0084] A method for preparing a monoamine-polycarboxyl-amphoteric viscoelastic surfactant comprises the following steps:

[0085] Add 10 ml of alkenyl succinic anhydride (R1 and R2 of ASA are straight-chain nonyl groups), 80 ml of toluene and 4 ml of dimethylformamide (DMF) into a three-necked flask equipped with a thermometer, an electric stirrer and a condenser, and stir and dissolve at 40°C;

[0086] Slowly add 2.4 g of triethanolamine solution into the dissolved three-necked flask, stir and heat to 80°C for 6 h;

[0087] After the reaction is completed, 0.66 g of chloroacetic acid is added and the reaction is continued at 65°C for 4 h;

[0088] After the reaction is completed, the product is evaporated to dryness using a rotary evaporator at a vacuum degree of 9 mmHg and a temperature of 80°C to obtain a solid crude product. The crude product is filtered, washed 5 times, and vacuum dried at 85°C for 7 hours to obtain a monoamino-polycarboxyl-ampholytic viscoelastic surfactant.

[0089] Example 5

[0090] A method for preparing a monoamine-polycarboxyl-amphoteric viscoelastic surfactant comprises the following steps:

[0091] Add 10 ml of alkenyl succinic anhydride (R1 and R2 of ASA are straight-chain decyl groups), 80 ml of toluene and 4 ml of dimethylformamide (DMF) into a three-necked flask equipped with a thermometer, an electric stirrer and a condenser, and stir and dissolve at 50°C;

[0092] Slowly add 2.4 g of triethanolamine solution into the dissolved three-necked flask, stir and heat to 75°C for 5 h;

[0093] After the reaction is completed, 0.61 g of chloroacetic acid is added and the reaction is continued at 65°C for 5 h;

[0094] After the reaction was completed, the product was evaporated to dryness using a rotary evaporator at a vacuum degree of 9 mmHg and a temperature of 80°C to obtain a solid crude product;

[0095] The crude product was filtered, washed 5 times, and vacuum dried at 85°C for 7 hours to obtain a monoamino-polycarboxyl-ampholytic viscoelastic surfactant.

[0096] Example 6

[0097] Monoamine-polycarboxyl-ampholytic viscoelastic surfactant, its structural formula is:

[0098] in:

[0099] R1 is a chain hexyl group;

[0100] R2 is a chain hexyl group.

[0101] A method for preparing a monoamine-polycarboxyl-amphoteric viscoelastic surfactant comprises the following steps:

[0102] (1) Add alkenyl succinic anhydride, toluene and N,N-dimethylformamide to a reaction vessel, heat to 40° C. and stir to obtain a mixed solution, wherein:

[0103] The volume ratio of alkenyl succinic anhydride, toluene and N,N-dimethylformamide is 8:70:3;

[0104] (2) Slowly add triethanolamine to the mixed solution obtained in step (1), stir evenly, heat to 60° C., and react for 6 hours to obtain a reaction solution, wherein:

[0105] The molar ratio of the triethanolamine to the alkenyl succinic anhydride is 1:3;

[0106] (3) Add chloroacetic acid to the reaction solution obtained in step (2), and then react at 50° C. for 6 hours to obtain a reaction solution, wherein:

[0107] The molar ratio of chloroacetic acid to triethanolamine is 1:1;

[0108] (4) evaporating the reaction solution obtained in step (3) to dryness to obtain a solid crude product;

[0109] (5) The solid crude product obtained in step (4) is filtered, washed multiple times, and vacuum dried to obtain a monoamine-polycarboxyl-ampholytic viscoelastic surfactant.

[0110] Furthermore, the reaction vessel in step (1) is a reaction vessel equipped with a thermometer, an electric stirrer and a condenser, preferably a three-necked flask.

[0111] Furthermore, in step (4), the reaction solution is evaporated to dryness by a rotary evaporator, and the vacuum degree of the rotary evaporator in step (4) is 8 mmHg.

[0112] Furthermore, the temperature of the rotary evaporator during evaporation in step (4) is controlled at 70°C.

[0113] Furthermore, the temperature of vacuum drying in step (5) is controlled at 80°C.

[0114] Furthermore, the vacuum drying time in step (5) is controlled within 8 hours.

[0115] The above monoamine-polycarboxyl-amphoteric viscoelastic surfactant is used as an oil displacement agent.

[0116] The above monoamine-polycarboxyl-ampholytic viscoelastic surfactant is used as a fracturing fluid.

[0117] Example 7

[0118] Monoamine-polycarboxyl-ampholytic viscoelastic surfactant, its structural formula is:

[0119] in:

[0120] R1 is a chain heptyl group;

[0121] R2 is a chain-like heptyl group.

[0122] A method for preparing a monoamine-polycarboxyl-amphoteric viscoelastic surfactant comprises the following steps:

[0123] (1) Add alkenyl succinic anhydride, toluene and N,N-dimethylformamide to a reaction vessel, heat to 50° C. and stir to obtain a mixed solution, wherein:

[0124] The volume ratio of alkenyl succinic anhydride, toluene and N,N-dimethylformamide is 12:90:5;

[0125] (2) Slowly add triethanolamine to the mixed solution obtained in step (1), stir evenly, heat to 80° C. and react for 4 hours to obtain a reaction solution, wherein:

[0126] The molar ratio of the triethanolamine to the alkenyl succinic anhydride is 1:3.5;

[0127] (3) Add chloroacetic acid to the reaction solution obtained in step (2), and then react at 70° C. for 4 hours to obtain a reaction solution, wherein:

[0128] The molar ratio of chloroacetic acid to triethanolamine is 1.1:1;

[0129] (4) evaporating the reaction solution obtained in step (3) to dryness to obtain a solid crude product;

[0130] (5) The solid crude product obtained in step (4) is filtered, washed multiple times, and vacuum dried to obtain a monoamine-polycarboxyl-ampholytic viscoelastic surfactant.

[0131] Furthermore, the reaction vessel in step (1) is a reaction vessel equipped with a thermometer, an electric stirrer and a condenser, preferably a three-necked flask.

[0132] Furthermore, in step (4), the reaction solution is evaporated to dryness by a rotary evaporator, and the vacuum degree of the rotary evaporator in step (4) is 10 mmHg.

[0133] Furthermore, the temperature of the rotary evaporator during evaporation in step (4) is controlled at 100°C.

[0134] Furthermore, the temperature of vacuum drying in step (5) is controlled at 100°C.

[0135] Furthermore, the vacuum drying time in step (5) is controlled within 5 hours.

[0136] The above monoamine-polycarboxyl-amphoteric viscoelastic surfactant is used as an oil displacement agent.

[0137] The above monoamine-polycarboxyl-ampholytic viscoelastic surfactant is used as a fracturing fluid.

[0138] Example 8

[0139] Monoamine-polycarboxyl-ampholytic viscoelastic surfactant, its structural formula is:

[0140] in:

[0141] R1 is a chain octyl group;

[0142] R2 is a chain octyl group.

[0143] A method for preparing a monoamine-polycarboxyl-amphoteric viscoelastic surfactant comprises the following steps:

[0144] (1) Add alkenyl succinic anhydride, toluene and N,N-dimethylformamide to a reaction vessel, heat to 45° C. and stir to obtain a mixed solution, wherein:

[0145] The volume ratio of alkenyl succinic anhydride, toluene and N,N-dimethylformamide is 10:80:4;

[0146] (2) Slowly add triethanolamine to the mixed solution obtained in step (1), stir evenly, heat to 70° C. and react for 5 hours to obtain a reaction solution, wherein:

[0147] The molar ratio of the triethanolamine to the alkenyl succinic anhydride is 1:3.2;

[0148] (3) Add chloroacetic acid to the reaction solution obtained in step (2), and then react at 60° C. for 5 hours to obtain a reaction solution, wherein:

[0149] The molar ratio of chloroacetic acid to triethanolamine is 1.05:1;

[0150] (4) evaporating the reaction solution obtained in step (3) to dryness to obtain a solid crude product;

[0151] (5) The solid crude product obtained in step (4) is filtered, washed multiple times, and vacuum dried to obtain a monoamine-polycarboxyl-ampholytic viscoelastic surfactant.

[0152] Furthermore, the reaction vessel in step (1) is a reaction vessel equipped with a thermometer, an electric stirrer and a condenser, preferably a three-necked flask.

[0153] Furthermore, in step (4), the reaction solution is evaporated to dryness by a rotary evaporator, and the vacuum degree of the rotary evaporator in step (4) is 8 mmHg.

[0154] Furthermore, the temperature of the rotary evaporator during evaporation in step (4) is controlled at 85°C.

[0155] Furthermore, the temperature of vacuum drying in step (5) is controlled at 90°C.

[0156] Furthermore, the vacuum drying time in step (5) is controlled within 6 hours.

[0157] The above monoamine-polycarboxyl-amphoteric viscoelastic surfactant is used as an oil displacement agent.

[0158] The above monoamine-polycarboxyl-ampholytic viscoelastic surfactant is used as a fracturing fluid.

[0159] Examples 9-10

[0160] It is substantially the same as Example 8, except that the substituents R1 and R2 are different:

[0161]

[0162] The above describes the embodiments of the present invention in detail. However, the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A monoamine-polycarboxyl-ampholytic viscoelastic surfactant, characterized in that: Its structural formula is: in: R1 is one of chain hexyl, heptyl, octyl, nonyl, and decyl; R2 is one of chain hexyl, heptyl, octyl, nonyl and decyl.

2. The monoamine-polycarboxyl-ampholytic viscoelastic surfactant according to claim 1, characterized in that: R1 is a chain octyl group; R2 is a chain octyl group.

3. The monoamine-polycarboxyl-ampholytic viscoelastic surfactant according to claim 2, characterized in that: R1 is a straight chain octyl group; R2 is a straight chain octyl group.

4. The method for preparing the monoamine-polycarboxyl-ampholytic viscoelastic surfactant according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Add alkenyl succinic anhydride, toluene and N,N-dimethylformamide to a reaction vessel, heat to 40-50° C., and stir to obtain a mixed solution, wherein: The volume ratio of alkenyl succinic anhydride, toluene and N,N-dimethylformamide is (8-12):(70-90):(3-5); The structural formula of the alkenyl succinic anhydride is as follows: The group definitions of R1 and R2 are as described in any one of claims 1 to 3; (2) Slowly add triethanolamine to the mixed solution obtained in step (1), stir evenly, heat to 60-80° C., react for 4-6 hours, and obtain a reaction solution, wherein: The molar ratio of the triethanolamine to the alkenyl succinic anhydride is 1:(3-3.5); (3) Add chloroacetic acid to the reaction solution obtained in step (2), and then react at 50 to 70° C. for 4 to 6 hours to obtain a reaction solution, wherein: The molar ratio of chloroacetic acid to triethanolamine is (1-1.1):1; (4) evaporating the reaction solution obtained in step (3) to dryness to obtain a solid crude product; (5) The solid crude product obtained in step (4) is filtered, washed multiple times, and vacuum dried to obtain a monoamine-polycarboxyl-ampholytic viscoelastic surfactant.

5. The method for preparing the monoamine-polycarboxyl-ampholytic viscoelastic surfactant according to claim 4, characterized in that: The reaction vessel in step (1) is a reaction vessel equipped with a thermometer, an electric stirrer and a condenser.

6. The method for preparing the monoamine-polycarboxyl-ampholytic viscoelastic surfactant according to claim 4, characterized in that: The volume ratio of alkenyl succinic anhydride, toluene and N,N-dimethylformamide in step (1) is 10:80:

4.

7. The method for preparing the monoamine-polycarboxyl-ampholytic viscoelastic surfactant according to claim 4, characterized in that: The molar ratio of triethanolamine to alkenyl succinic anhydride added in step (2) is 1:

3.

8. The method for preparing the monoamine-polycarboxyl-ampholytic viscoelastic surfactant according to claim 4, characterized in that: The molar ratio of chloroacetic acid to triethanolamine added in step (3) is 1.05:

1.

9. The method for preparing the monoamine-polycarboxyl-ampholytic viscoelastic surfactant according to claim 4, characterized in that: In step (4), the reaction solution is evaporated to dryness by a rotary evaporator, and the vacuum degree of the rotary evaporator in step (4) is 8 to 10 mmHg.

10. The method for preparing the monoamine-polycarboxyl-ampholytic viscoelastic surfactant according to claim 9, characterized in that: In step (4), the temperature of the rotary evaporator during evaporation is controlled at 70-100°C.

11. The method for preparing the monoamine-polycarboxyl-ampholytic viscoelastic surfactant according to claim 4, characterized in that: The temperature of vacuum drying in step (5) is controlled at 80-100°C.

12. The method for preparing the monoamine-polycarboxyl-ampholytic viscoelastic surfactant according to claim 4, characterized in that: The vacuum drying time in step (5) is controlled to be 5 to 8 hours.

13. Use of the monoamine-polycarboxyl amphoteric viscoelastic surfactant described in any one of claims 1 to 3 or the monoamine-polycarboxyl amphoteric viscoelastic surfactant prepared by the preparation method described in any one of claims 4 to 12 as an oil displacing agent.

14. Use of the monoamine-polycarboxyl amphoteric and viscoelastic surfactant according to any one of claims 1 to 3 or the monoamine-polycarboxyl amphoteric and viscoelastic surfactant prepared by the preparation method according to any one of claims 4 to 12 as a fracturing fluid.

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