A viscoelastic surfactant, its preparation method and application

Abstract

This invention discloses a viscoelastic surfactant, its preparation method, and its applications. The viscoelastic surfactant comprises at least one compound with the structure shown in formula (I): wherein R is selected from one of the following: substituted or unsubstituted C1-C30 straight-chain hydrocarbon groups, substituted or unsubstituted C3-C30 branched hydrocarbon groups, substituted or unsubstituted C3-C30 cycloalkyl groups, C6-C30 aromatic groups, aromatic groups substituted with C1-C30 straight-chain hydrocarbon groups, aromatic groups substituted with C3-C30 branched hydrocarbon groups, and aromatic groups substituted with C3-C30 cycloalkyl groups. The viscoelastic surfactant production process provided by this invention is simple, with mild and easily controllable conditions, and is a relatively green chemical process. The viscoelastic surfactant product exhibits good oil-water interfacial activity, and the unary system possesses considerable viscosity, thus showing great application potential in tertiary oil recovery processes, especially in low-permeability and ultra-low-permeability reservoirs.

Description

Technical Field

[0001] This invention relates to the field of surfactant technology, specifically to a viscoelastic surfactant, its preparation method, and its application. Background Technology

[0002] After decades of water injection development, most of my country's onshore oilfields have entered a stage of high water cut and high recovery. Especially in older oilfields, which are now in the late stages of secondary oil recovery, the "double high" stage of high water cut and high recovery is becoming increasingly difficult, making stable waterflooding production more challenging and creating a severe development situation. Therefore, the exploitation of difficult-to-access reserves in high-temperature, high-salinity, heavy oil, and low-permeability reservoirs is becoming increasingly urgent. Recent indoor research and field practice results on chemical flooding in high-temperature, high-salinity, and low-permeability reservoirs indicate that, due to the large molecular size of polymers and the need to improve their temperature and salt resistance, surfactant flooding is the most promising chemical flooding technology for these reservoirs.

[0003] Traditionally, research on surfactants for oil displacement has focused on their ultra-low interfacial tension, high temperature resistance, and resistance to high salt and high calcium / magnesium content. However, recent research has shown a growing interest in surfactants with thickening properties. Optimal surfactant solution viscosity can enhance the sweep efficiency of surfactant-based flooding, significantly improving displacement efficiency in field applications compared to water flooding or active water flooding. Furthermore, the unary systems formed by these surfactants can leverage the combined effects of polymers and surfactants in composite flooding while avoiding chromatographic separation issues common in such applications.

[0004] CN108559474A provides a cationic amphiphilic polymer supramolecular oil displacement system, which can effectively reduce the amount of polymer used, increase the viscosity of the amphiphilic polymer oil displacement system, and improve the swept volume and oil displacement efficiency. However, since this system is a polymer-small molecule complex system, chromatographic separation problems during the oil displacement process cannot be avoided.

[0005] CN114181685A discloses a water-driven heavy oil viscous self-emulsifying moderating system. This system has a certain viscosity, which can expand the swept volume and can be applied to the development of ordinary heavy oil reservoirs. However, this system does not have the performance of ultra-low interfacial tension and still needs to be compounded with surfactants in the tertiary oil recovery process.

[0006] Furthermore, for unary viscoelastic systems used in low-permeability and ultra-low-permeability reservoirs, there are further requirements on the molecular size of the corresponding surfactants, especially since polymers or oligomers may present injection difficulties.

[0007] Therefore, there is an urgent need for a single viscoelastic surfactant with ultra-low interfacial tension, no need for compounding, and suitable molecular size for injection. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a viscoelastic surfactant, its preparation method, and its application.

[0009] One object of the present invention is to provide a viscoelastic surfactant comprising at least one of compounds with the structure shown in formula (I) below:

[0010]

[0011] Wherein, R is selected from one of the following: substituted or unsubstituted C1-C30 straight-chain hydrocarbon groups, substituted or unsubstituted C3-C30 branched hydrocarbon groups, substituted or unsubstituted C3-C30 cycloalkyl groups, C6-C30 aromatic groups, aromatic groups substituted with C1-C30 straight-chain hydrocarbon groups, aromatic groups substituted with C3-C30 branched hydrocarbon groups, and aromatic groups substituted with C3-C30 cycloalkyl groups.

[0012] In a preferred embodiment of the present invention,

[0013] The substituted C1-C30 straight-chain hydrocarbon group, the substituted C3-C30 branched hydrocarbon group, and the substituted C3-C30 cycloalkyl group may be the same or different, and are each independently selected from at least one of the C1-C30 straight-chain hydrocarbon group, the C3-C30 branched hydrocarbon group, and the C3-C30 cycloalkyl group; and / or,

[0014] R is selected from one of the following: substituted or unsubstituted C1-C24 straight-chain hydrocarbon groups, substituted or unsubstituted C3-C24 branched hydrocarbon groups, substituted or unsubstituted C3-C24 cycloalkyl groups, C6-C24 aromatic groups, aromatic groups substituted with C1-C24 straight-chain hydrocarbon groups, aromatic groups substituted with C3-C24 branched hydrocarbon groups, and aromatic groups substituted with C3-C24 cycloalkyl groups, preferably one of C1-C24 straight-chain alkyl groups, C3-C24 branched alkyl groups, and C3-C24 cycloalkyl groups. More preferably, it is one of C5 to C20 straight-chain alkyl and C5 to C20 branched alkyl, for example, it can be C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C20 straight-chain alkyl or C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C20 branched alkyl.

[0015] A second objective of this invention is to provide a method for preparing a viscoelastic surfactant, which is one of the objectives of this invention, comprising:

[0016] Ethylenediamine-N,N'-diacetic acid and a base are dissolved in solvent 1, and then a haloalkane and solvent 2 are added to react and obtain the viscoelastic surfactant.

[0017] This method involves removing hydrogen atoms from the nitrogen atom of ethylenediamine-N,N'-diacetic acid with an alkali to form an N-anion. One of the N-anions undergoes an SN2 nucleophilic reaction with a haloalkane, while the other N-anion attacks the carbonyl group to form a six-membered ring lactam, thus obtaining a viscoelastic surfactant with the structure of formula (I). In this invention, the compound with the structure of formula (I) is deduced from the reactants and the reaction mechanism.

[0018] In a preferred embodiment of the present invention,

[0019] The alkali is at least one selected from alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates, alkali metal phosphates, alkali metal hydrogen phosphates, and alkali metal salts of alcohols, preferably one or more selected from sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, potassium phosphate, potassium hydrogen phosphate, sodium phosphate, sodium methoxide, and sodium ethoxide; and / or,

[0020] Solvent 1 and solvent 2 may be the same or different, and are each independently at least one of organic solvents and inorganic solvents, preferably one or more of methanol, ethanol, isopropanol, acetonitrile, benzene, toluene, chloroform, N,N-dimethylformamide, N-methylpyrrolidone, and water; more preferably, solvent 1 and solvent 2 are different, and the polarity of solvent 1 is greater than that of solvent 2; solvent 2 is mainly used to dissolve halogenated hydrocarbons; and / or,

[0021] The general formula of the haloalkane is R'X, wherein R' is selected from one of the following: substituted or unsubstituted C1-C30 straight-chain hydrocarbon group, substituted or unsubstituted C3-C30 branched hydrocarbon group, substituted or unsubstituted C3-C30 cycloalkyl group, C6-C30 aromatic group, aromatic group substituted with C1-C30 straight-chain hydrocarbon group, aromatic group substituted with C3-C30 branched hydrocarbon group, and aromatic group substituted with C3-C30 cycloalkyl group; and / or, X is selected from one of the halogen atoms, preferably one of fluorine, chlorine, bromine, and iodine.

[0022] In a preferred embodiment of the present invention,

[0023] In the aforementioned haloalkanes, the substituents in the substituted C1-C30 straight-chain hydrocarbon groups, the substituted C3-C30 branched hydrocarbon groups, and the substituted C3-C30 cycloalkyl groups may be the same or different, and are each independently selected from at least one of the C1-C30 straight-chain hydrocarbon groups, C3-C30 branched hydrocarbon groups, and C3-C30 cycloalkyl groups; and / or,

[0024] R' is selected from one of the following: substituted or unsubstituted C1-C24 straight-chain hydrocarbon groups, substituted or unsubstituted C3-C24 branched hydrocarbon groups, substituted or unsubstituted C3-C24 cycloalkyl groups, C6-C24 aromatic groups, aromatic groups substituted with C1-C24 straight-chain hydrocarbon groups, aromatic groups substituted with C3-C24 branched hydrocarbon groups, and aromatic groups substituted with C3-C24 cycloalkyl groups, preferably one of C1-C24 straight-chain alkyl groups, C3-C24 branched alkyl groups, and C3-C24 cycloalkyl groups. More preferably, it is one of C5 to C20 straight-chain alkyl and C5 to C20 branched alkyl, for example, it can be C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C20 straight-chain alkyl or C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C20 branched alkyl.

[0025] In a preferred embodiment of the present invention,

[0026] The molar ratio of the base to ethylenediamine-N,N'-diacetic acid is (2.0–40.0):1, preferably (2.0–20.0):1, more preferably (2.0–6.0):1; and / or,

[0027] The mass ratio of solvent 1 to ethylenediamine-N,N'-diacetic acid is (0.01-100.0):1, preferably (1.0-10.0):1, and more preferably (5.0-10.0):1.

[0028] In a preferred embodiment of the present invention,

[0029] The dissolution temperature is 20–100°C, preferably 30–80°C; and / or the dissolution time is 10–120 minutes, preferably 20–60 minutes.

[0030] In a preferred embodiment of the present invention,

[0031] The molar ratio of the haloalkane to ethylenediamine-N,N'-diacetic acid is (0.8–2.5):1, preferably (1.0–1.5):1, more preferably (1.0–1.2):1; and / or,

[0032] The mass ratio of solvent 2 to ethylenediamine-N,N'-diacetic acid is (0.01-100.0):1, preferably (1.0-20.0):1, and more preferably (5.0-12.0):1.

[0033] In a preferred embodiment of the present invention,

[0034] The reaction temperature is 20–120°C, preferably 50–100°C, more preferably 85–100°C; and / or the reaction time is 3–48 hours, preferably 5–24 hours, more preferably 12–24 hours.

[0035] In a preferred embodiment of the present invention,

[0036] The reaction process, after adding the haloalkane and solvent 2, further includes a post-treatment step of the reaction product; preferably, the post-treatment includes removing the solvent from the reaction product and then acidifying it; more preferably, the post-treatment includes filtering the obtained reaction product, evaporating the solvent, washing, and then acidifying it; even more preferably...

[0037] The washing agent is an organic solvent, preferably a C5-C12 alkane; and / or,

[0038] The acidification reagent used is an inorganic acid solution, preferably a 0.1-5 mol / L dilute hydrochloric acid.

[0039] The preparation method of the viscoelastic surfactant of the present invention can adopt the following specific technical solutions:

[0040] (1) Dissolve the raw material ethylenediamine-N,N'-diacetic acid and the base in solvent 1 by heating;

[0041] (2) Add haloalkanes and solvent 2 to the reaction system of step (1), mix, heat to react, and after the reaction is completed, the viscoelastic surfactant is obtained by post-treatment.

[0042] A third objective of this invention is to provide an application of a viscoelastic surfactant obtained by one of the objectives of this invention or by the preparation method of another objective of this invention in tertiary oil recovery.

[0043] The concentration of the viscoelastic surfactant of the present invention used in tertiary oil recovery is not particularly limited, and is mainly determined according to the field plan.

[0044] A fourth objective of this invention is to provide an oil displacement agent comprising a viscoelastic surfactant as described in one objective of this invention or a viscoelastic surfactant prepared by the method described in another objective of this invention.

[0045] The beneficial effects of this invention are:

[0046] The viscoelastic surfactant production process provided by this invention is simple, with mild and easily controllable conditions, making it a relatively green chemical process. The viscoelastic surfactant product exhibits good oil-water interfacial activity, and the unary system possesses considerable viscosity, thus showing great application potential in tertiary oil recovery processes, especially in low-permeability and ultra-low-permeability reservoirs. Attached Figure Description

[0047] Figure 1 The mass spectrometry characterization (positive ion mode ESI+) of the viscoelastic surfactant prepared in Example 1 of this invention is shown; where the horizontal axis represents the mass-to-charge ratio (m / z) of the ions and the vertical axis represents the intensity of the ion current.

[0048] Figure 2 The mass spectrometry characterization (negative ion mode ESI-) of the viscoelastic surfactant prepared in Example 1 of this invention is shown; where the horizontal axis represents the mass-to-charge ratio (m / z) of the ions, and the vertical axis represents the intensity of the ion current. Detailed Implementation

[0049] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0050] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0051] The mass spectrometry characterization in this invention was obtained by testing with a WATERS 3100MSD mass spectrometer.

[0052] Example 1

[0053] Add 1 mole of ethylenediamine-N,N'-diacetic acid, 5 times the weight of isopropanol and 1 times the weight of water to the reaction flask, heat the system to 70°C while stirring at 700 rpm, add 2 moles of potassium carbonate and stir for 30 minutes.

[0054] Then, 1 mole of hexadecane bromo and 10 times the weight of acetonitrile (i.e., the weight of acetonitrile is 10 times that of ethylenediamine-N,N'-diacetic acid) were added. The system was heated to 90°C with stirring, and the reaction was stopped after stirring for 16 hours. The mixture was filtered, the solvent was removed by rotary evaporation, washed with n-hexane, and acidified with 1M dilute hydrochloric acid for 30 minutes. The product with the following structure was obtained by filtration. R is a C16 straight-chain alkyl group, and the yield is 64%.

[0055] Figure 1 and Figure 2The images show the mass spectrometry characterization of the viscoelastic surfactant prepared in Example 1 of this invention in positive ion mode and negative ion mode, respectively. [M+H] 383.3 (positive ion mode) and [MH] 381.3 (negative ion mode) indicate that the molecular weight of the viscoelastic surfactant molecule prepared in Example 1 of this invention is 382. Therefore, based on the reactants and reaction mechanism, it can be inferred that the viscoelastic surfactant prepared in Example 1 of this invention possesses the above-mentioned structure.

[0056] Example 2

[0057] Add 1 mole of ethylenediamine-N,N'-diacetic acid, 4 times the weight of ethanol and 1 times the weight of water to the reaction flask, heat the system to 65°C while stirring at 700 rpm, add 3 moles of sodium carbonate, and stir for 40 minutes.

[0058] Then, 1.2 moles of octadecane bromide and acetonitrile in a 12-fold weight ratio (i.e., the weight of acetonitrile is 12 times that of ethylenediamine-N,N'-diacetic acid) were added. The system was heated to 95°C with stirring, and the reaction was stopped after stirring for 20 hours. The mixture was filtered, the solvent was removed by rotary evaporation, washed with n-hexane, and acidified with 1M dilute hydrochloric acid for 30 minutes. The product with the following structure was obtained by filtration. R is a C18 straight-chain alkyl group, and the yield is 73%.

[0059] Example 3

[0060] Add 1 mole of ethylenediamine-N,N'-diacetic acid, 6 times the weight of DMF and 1 times the weight of water to the reaction flask, heat the system to 55°C while stirring at 700 rpm, add 4 moles of sodium phosphate, and stir for 25 minutes.

[0061] Then, 1 mole of tetradecyl chloride and 6 times the weight of DMF (i.e., the weight of DMF is 6 times that of ethylenediamine-N,N'-diacetic acid) were added. The system was heated to 100°C with stirring, and the reaction was stopped after stirring for 24 hours. The mixture was filtered, the solvent was removed by rotary evaporation, washed with n-hexane, and acidified with 1M dilute hydrochloric acid for 30 minutes. The product with the following structure was obtained by filtration. R is a C14 straight-chain alkyl group, and the yield is 63%.

[0062] Example 4

[0063] Add 1 mole of ethylenediamine-N,N'-diacetic acid, 9 times the weight of isopropanol and 1 times the weight of water to the reaction flask, heat the system to 50°C while stirring at 700 rpm, add 2 moles of potassium carbonate and stir for 30 minutes.

[0064] Then, 1 mole of bromododecane and 10 times the weight of acetonitrile (i.e., the weight of acetonitrile is 10 times that of ethylenediamine-N,N'-diacetic acid) were added. The system was heated to 90°C with stirring, and the reaction was stopped after stirring for 20 hours. The mixture was filtered, the solvent was removed by rotary evaporation, washed with n-hexane, and acidified with 1M dilute hydrochloric acid for 30 minutes. The product with the following structure was obtained by filtration. R is a C12 straight-chain alkyl group, and the yield is 62%.

[0065] Example 5

[0066] Add 1 mole of ethylenediamine-N,N'-diacetic acid, 4 times the weight of ethanol and 1 times the weight of water to the reaction flask, heat the system to 65°C while stirring at 700 rpm, add 3 moles of potassium carbonate and stir for 40 minutes.

[0067] Then, 1.2 moles of bromo-isotridecane and 10 times the weight of toluene (i.e., toluene by weight 10 times the weight of ethylenediamine-N,N'-diacetic acid) were added. The system was heated to 85°C with stirring, and the reaction was stopped after stirring for 20 hours. The mixture was filtered, the solvent was removed by rotary evaporation, washed with n-hexane, and acidified with 1M dilute hydrochloric acid for 30 minutes. The product with the following structure was obtained by filtration. R is an isomeric tridecyl group, with a yield of 60%.

[0068] Comparative Example 1

[0069] The ethylenediamine-N,N'-diacetic acid used in Example 1 was mixed with hexadecane bromo in equimolar amounts to obtain a composition.

[0070] Test case

[0071] Determination of oil-water interfacial tension and viscosity

[0072] The samples from Examples 1-5 and Comparative Example 1 were diluted to different weight percentage concentrations using produced water from the Shengli Oilfield. The interfacial tension between the diluted solutions and Shengli Oilfield crude oil was then measured using a TX-500C rotating drop interfacial tensiometer. The interfacial tension of the diluted solutions at 7.34 s⁻¹ was measured using an Anton Paar MCR702 rheometer. -1 The viscosity under shear is shown in Tables 1 and 2.

[0073] Table 1: Interfacial tension data (mN / m) between 0.2 wt% solution and Shengli Oilfield crude oil

[0074] Interfacial tension mN / m Example 1 0.00533 Example 2 0.00497 Example 3 0.00694 Example 4 0.00791 Example 5 0.00925 Comparative Example 1 2.339

[0075] Table 2: Viscosity (mPa·s) of 0.1 wt% concentration solution at formation temperature (40 °C)

[0076] Viscosity mPa·s Example 1 10.23 Example 2 9.88 Example 3 8.57 Example 4 9.56 Example 5 5.40 Comparative Example 1 1.0

[0077] As can be seen from Examples 1-5, Comparative Example 1, and Tables 1 and 2, compared with the simple mixing of ethylenediamine-N,N'-diacetic acid and haloalkanes (Comparative Example 1), the viscoelastic surfactant with the structure shown in Formula (I) obtained by reacting ethylenediamine-N,N'-diacetic acid with haloalkanes in this invention has significantly better oil-water interfacial activity and more considerable viscosity. Therefore, it has good application prospects in tertiary oil recovery, especially in low-permeability and ultra-low-permeability reservoirs.

[0078] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[0079] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0080] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0081] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values; such ranges or values ​​should be understood to include values ​​close to them. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0082] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

[0083] Furthermore, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or technical ideas shall be regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider the combination to be obviously unreasonable.

Claims

1. A viscoelastic surfactant comprising at least one of the compounds represented by the following formula (I) : wherein R is selected from one of substituted or unsubstituted C1-C30 linear alkyl, substituted or unsubstituted C3-C30 branched alkyl, substituted or unsubstituted C3-C30 cyclic alkyl, C6-C30 aromatic group, C1-C30 linear alkyl substituted aromatic group, C3-C30 branched alkyl substituted aromatic group, C3-C30 cyclic alkyl substituted aromatic group. wherein 2.The viscoelastic surfactant of claim 1, wherein the substituted C1-C30 linear alkyl, the substituted C3-C30 branched alkyl, the substituted C3-C30 cyclic alkyl are independently selected from at least one of C1-C30 linear alkyl, C3-C30 branched alkyl, C3-C30 cyclic alkyl, respectively, and / or the substituents of the substituted C1-C30 linear alkyl, the substituted C3-C30 branched alkyl, the substituted C3-C30 cyclic alkyl are the same or different, and R is selected from one of substituted or unsubstituted C1-C24 linear alkyl, substituted or unsubstituted C3-C24 branched alkyl, substituted or unsubstituted C3-C24 cyclic alkyl, C6-C24 aromatic group, C1-C24 linear alkyl substituted aromatic group, C3-C24 branched alkyl substituted aromatic group, C3-C24 cyclic alkyl substituted aromatic group, preferably one of C1-C24 linear alkyl, C3-C24 branched alkyl, C3-C24 cyclic alkyl. 3.A method for preparing a viscoelastic surfactant, preferably a method for preparing the viscoelastic surfactant of any one of claims 1-2, the method comprising: dissolving ethylenediamine-N, N'-diacetic acid and a base in a solvent 1, and then adding a halogenated hydrocarbon and a solvent 2 to react, to obtain the viscoelastic surfactant. 4.The method of claim 3, wherein the base is at least one of alkali metal hydroxide, alkali metal carbonate, alkali metal bicarbonate, alkali metal phosphate, alkali metal hydrogen phosphate, alkali metal alcoholate, preferably one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, potassium phosphate, potassium hydrogen phosphate, sodium phosphate, sodium methoxide, sodium ethoxide, and / or the solvent 1 and the solvent 2 are independently at least one of organic solvent, inorganic solvent, preferably one or more of methanol, ethanol, isopropanol, acetonitrile, benzene, toluene, chloroform, N, N-dimethylformamide, N-methylpyrrolidone, water, and / or the halogenated hydrocarbon has a general formula of R'X, wherein R' is selected from one of substituted or unsubstituted C1-C30 linear alkyl, substituted or unsubstituted C3-C30 branched alkyl, substituted or unsubstituted C3-C30 cyclic alkyl, C6-C30 aromatic group, C1-C30 linear alkyl substituted aromatic group, C3-C30 branched alkyl substituted aromatic group, C3-C30 cyclic alkyl substituted aromatic group, and / or X is selected from one of halogen atoms, preferably one of fluorine, chlorine, bromine, iodine. 5.The method of claim 3, wherein ​ ​ ​ ​ ​ ​ ​ The molar ratio of the base to ethylenediamine-N,N'-diacetic acid is (2.0–40.0):1, preferably (2.0–20.0):1; and / or, The mass ratio of solvent 1 to ethylenediamine-N,N'-diacetic acid is (0.01-100.0):1, preferably (1.0-10.0):

1.

6. The preparation method according to claim 3, characterized in that: The dissolution temperature is 20–100°C, preferably 30–80°C; and / or the dissolution time is 10–120 minutes, preferably 20–60 minutes.

7. The preparation method according to claim 3, characterized in that: The molar ratio of the haloalkane to ethylenediamine-N,N'-diacetic acid is (0.8–2.5):1, preferably (1.0–1.5):1; and / or, The mass ratio of solvent 2 to ethylenediamine-N,N'-diacetic acid is (0.01-100.0):1, preferably (1.0-20.0):

1.

8. The preparation method according to claim 3, characterized in that: The reaction temperature is 20–120°C, preferably 50–100°C; and / or the reaction time is 3–48 hours, preferably 5–24 hours.

9. The preparation method according to claim 3, characterized in that: The reaction process, after adding the haloalkane and solvent 2, further includes a post-treatment step of the reaction product; preferably, the post-treatment includes removing the solvent from the reaction product and then acidifying it; more preferably, the post-treatment includes filtering the obtained reaction product, evaporating the solvent, washing, and then acidifying it; even more preferably... The washing agent is an organic solvent, preferably a C5-C12 alkane; and / or, The acidification reagent used is an inorganic acid solution, preferably a 0.1-5 mol / L dilute hydrochloric acid.

10. The application of a viscoelastic surfactant as described in any one of claims 1-2 or a viscoelastic surfactant obtained by the preparation method as described in any one of claims 3-9 in tertiary oil recovery.

11. An oil displacement agent comprising a viscoelastic surfactant as described in any one of claims 1-2 or a viscoelastic surfactant obtained by the preparation method as described in any one of claims 3-9.

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