An amino acid-based amphoteric / anionic surfactant oil displacement system, its preparation method and application

Abstract

This invention discloses an amino acid-based amphoteric / anionic surfactant oil displacement system, its preparation method, and its application. The system comprises an amino acid-based amphoteric surfactant and sodium dodecylbenzenesulfonate, wherein the molar ratio of the amino acid-based amphoteric surfactant to sodium dodecylbenzenesulfonate is 1:1. The amino acid-based amphoteric surfactant is prepared by amidation reaction of a compound of formula I or its salt with a fatty amine. Its isoelectric point is near formation water (pH = 6-8), exhibiting significant bipolarity in formation water environments (pH = 6-8). Utilizing an amino acid-based amphoteric / anionic surfactant allows for the green, efficient, and convenient preparation of responsive oil-in-water emulsions, potentially offering new insights and inspirations for amino acid-based surfactant oil displacement.

Description

Technical Field

[0001] This invention belongs to the field of oilfield oil production technology, specifically relating to an amino acid-based amphoteric / anionic surfactant oil displacement system, its preparation method, and its application. Background Technology

[0002] With energy demand constantly rising and my country's dependence on imported crude oil exceeding 70%, the country's energy security is severely threatened. Under these circumstances, the importance of tertiary oil recovery is self-evident. Surfactant flooding is one such method within tertiary oil recovery. In reports on surfactant flooding, the combination of two surfactants with different charges exhibits good synergistic effects and oil displacement mechanisms. Among studies of anionic / cationic surfactants, zwitterionic / anionic surfactants, and zwitterionic / cationic surfactant composite systems, the zwitterionic / anionic surfactant composite system shows better application results, primarily due to lower adsorption losses and better synergistic effects at the interface. In the selection of zwitterionic surfactants, most studies focus on betaine, with very few choosing amino acid-based surfactants. However, amino acid-based surfactants possess a structure similar to betaine, and in reported cases of amino acid surfactant flooding, this environmentally friendly surfactant demonstrates good oil displacement performance.

[0003] Amino acid surfactants are a class of surfactants with abundant raw materials and easy synthesis. However, because the amino groups in amino acid surfactants have a weak positive charge and the carboxyl groups have a strong negative charge, these surfactants often exhibit negative charge in formation water environments (pH=6-8). Anionic surfactants, on the other hand, have poor temperature and salt tolerance, and amino acid surfactants, when used alone, have poor emulsifying properties and the ability to reduce interfacial tension. Therefore, amino acid surfactants are often used as foaming agents in the petroleum industry. In recent years, some researchers have synthesized amino acid-based gemini surfactants, which possess high interfacial activity and emulsifying properties. However, very few studies have reported on the oil displacement effects of combining amino acid surfactants with anionic surfactants. This is because the isoelectric point of amino acid surfactants is too low, exhibiting only negative charge under formation conditions, resulting in an antagonistic effect with anionic surfactants. Summary of the Invention

[0004] One of the objectives of this invention is to provide an amino acid-type amphoteric surfactant.

[0005] The amino acid-type amphoteric surfactant provided by this invention has an isoelectric point near formation water (pH=6-8), and exhibits two distinct electrical properties in the formation water environment (pH=6-8).

[0006] The amino acid-type amphoteric surfactant provided by this invention is prepared by reacting a compound of Formula I or its salt with a fatty amine via an amidation reaction. , In formula I, n = 8 - 18. In embodiments of the present invention, the compound represented by Formula I is lauroyl glutamic acid or a salt thereof; The fatty amine may be selected from at least one of: triethylenetetramine and ethylenediamine.

[0007] Specifically, the above-mentioned amino acid-type amphoteric surfactant is prepared by a method comprising the following steps: 1) Sodium lauroyl glutamate was added to water and ultrasonically dispersed. Then, excess fatty amine and catalysts 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide were added, and the resulting solution was ultrasonically dispersed again. 2) Adjust the reaction environment of the prepared solution, and adjust the overall pH of the solution to a slightly acidic pH of 4-5; 3) The solution was reacted under stirring. The reaction temperature was set to room temperature for the first 5 hours, and then the temperature was increased while stirring was continued to obtain the modified sodium lauroyl glutamate. 4) Allow the solution containing the product to stand at low temperature, remove the supernatant and centrifuge it, and pour the solid obtained by centrifugation into the turbid liquid (the turbid liquid refers to the liquid after the supernatant has been separated); 5) The treated turbid liquid was placed in a refrigerator for dialysis. After dialysis, the liquid was evaporated to the volume of the solution to remove most of it. The solution was then freeze-dried to obtain the final product TFDA.

[0008] In step 1) of the above method, the fatty amine may be selected from at least one of: triethylenetetramine and ethylenediamine; In the resulting solution, the molar concentration of sodium lauroyl glutamate can be 0.01-0.02 mol / L, and the amino acid concentration dispersed in the aqueous solution is approximately 0.004-0.008 mol / L. The molar concentration of fatty amines is approximately 0.6-0.8 mol / L; The catalyst has a mass ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide to N-hydroxysuccinimide of 2:1. The catalyst, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, is added in an amount of 0.01-0.03 mol / L. In step 2) of the above method, the acids used to adjust the pH are sulfuric acid and hydrochloric acid. Sulfuric acid is added first, and the remaining acid is hydrochloric acid to adjust the pH. The molar ratio of sodium lauroyl glutamate to sulfuric acid is 10:83; In step 3) of the above method, after 5 hours of reaction at room temperature, the temperature is raised to 50 °C, and then stirring is continued for 43 hours. The stirring speed is 400-600 rpm.

[0009] In step 4) of the above method, the temperature of the low-temperature standing can be 0 ℃, and the time can be 5-10 h, specifically 5 h; The centrifuge speed was 8000 rpm, and the centrifugation time was 8 minutes; In step 5) of the above method, the dialysis time is greater than or equal to 1 day, and the dialysis temperature is 0 ℃.

[0010] The second objective of this invention is to provide an amino acid-based amphoteric / anionic surfactant compound system.

[0011] The amino acid-type amphoteric / anionic surfactant compound system provided by the present invention is composed of the above-mentioned amino acid-type amphoteric surfactant and sodium dodecylbenzene sulfonate, wherein the molar ratio of amino acid-type amphoteric surfactant to sodium dodecylbenzene sulfonate is 1:1. The amino acid-type amphoteric surfactant may specifically be the amino acid-type amphoteric surfactant TFDA.

[0012] This invention utilizes a dehydration condensation reaction to graft aliphatic amines (triethylenetetramine, ethylenediamine, etc.) onto the side chains of sodium lauroyl glutamate. Since the carboxyl group on the sodium lauroyl glutamate backbone does not participate in the reaction, the resulting product TFDA still possesses a carboxyl group. The structure of TFDA is characterized by mass spectrometry, 1H NMR, 1C NMR, and Zeta potential. Figure 1 Nuclear magnetic resonance C-spectrum Figure 2 1H NMR spectrum Figure 3 Zeta potential at different pH values Figure 4 Mass spectrometry (MS / MS) shows that TFDA dissolves well in water and heavy water only in slightly alkaline or neutral environments. The carboxyl group in the TFDA tail chain is partially protonated in alkaline environments, resulting in two product peaks in the MS / MS. Literature reports that sodium lauroyl glutamate exhibits different degrees of protonation of the two carboxyl groups at different pH values. NMR spectroscopy and other literature support the conclusion that the carboxyl groups on the main chain do not participate in the reaction. Experiments demonstrate that in an environment with pH 6-8, the positive charge and negative charge of the amino acid-type surfactant grafted with four amino groups are most similar. At this pH, the amino acid-type amphoteric surfactant achieves the best synergistic effect with the anionic surfactant sodium dodecylbenzenesulfonate at the oil-water interface under formation water conditions (mixed adsorption and competitive adsorption at the interface).

[0013] The second objective of this invention is to provide the above-mentioned amino acid amphoteric / anionic surfactant as a stabilizer for stabilizing emulsions.

[0014] The present invention also provides a stable oil-in-water emulsion with pH responsive properties.

[0015] The stable oil-in-water emulsion with pH-responsive properties provided by this invention is prepared by a method comprising the following steps: The above-mentioned surfactant compound system was dispersed in NaCl salt aqueous solution, and the pH value of the prepared surfactant salt aqueous solution was adjusted to between 6 and 8 to obtain surfactant salt aqueous solution; the prepared surfactant solution was used as an emulsifier and mixed with simulated oil, and stirred to obtain an oil-in-water emulsion with pH responsive properties.

[0016] The NaCl concentration in the NaCl salt aqueous solution can be 0.5-2 wt.%, specifically 0.5 wt.%, 1 wt.%, 1.5 wt.%, or 2 wt.%. In the surfactant salt solution, the total concentration of the surfactant complex system is 0.3 wt.%, and the molar ratio of the two surfactants is 1:1. The simulated oil is made by mixing crude oil and kerosene, wherein the mass ratio of crude oil to kerosene is 1:2. The oil-to-water ratio of the emulsion is 3:7.

[0017] This invention provides a surfactant blend system with pH-responsive properties. Because the amphoteric surfactant has positively charged groups, it adsorbs with sodium dodecylbenzenesulfonate at the interface, forming a dense adsorption layer. Since the amphoteric surfactant also carries negatively charged groups, it competes with sodium dodecylbenzenesulfonate at the interface for the adsorption of positively charged groups. Simultaneously, electrostatic repulsion prevents the amphoteric surfactant from forming ion pairs with anionic surfactants due to excessive electrostatic attraction. Furthermore, the surfactant blend system has low water solubility, allowing the surfactant to quickly find the oil-water interface at low stirring rates, forming a large amount of emulsion with small particle size. The surface of the formed emulsion is covered with a dense adsorption film formed by the surfactant blend system, resulting in a more stable emulsion with a significantly reduced aggregation rate. Because the charge of the amphoteric surfactant varies in solutions with different pH levels, the positive charge of the amino acid-type surfactant increases in acidic environments, while the ionization of the carboxyl groups gradually weakens, leading to a decrease in the negative charge. At this point, due to the increased electrostatic attraction and decreased electrostatic repulsion, the two surfactants form ion pairs, leading to emulsion demulsification. The use of amino acid amphoteric / anionic surfactants to prepare responsive oil-in-water emulsions in a green, efficient, and convenient manner holds promise for providing new insights and inspirations for oil displacement using amino acid-based surfactants.

[0018] The above-mentioned surfactant compound system can reduce the interfacial tension between oil and water to a low level.

[0019] The present invention also provides a system capable of reducing the interfacial tension between oil and water to a low level.

[0020] The system provided by this invention, capable of reducing the interfacial tension between oil and water to a low level, is prepared by a method comprising the following steps: The above-mentioned surfactant compound system was dispersed in NaCl salt aqueous solution, and the pH value of the prepared surfactant salt aqueous solution was adjusted to between 6 and 8.

[0021] The mass concentration of NaCl in the NaCl salt aqueous solution can be 0.5-2 wt.%, specifically 0.5 wt.%, 1 wt.%, 1.5 wt.%, or 2 wt.%. In the system, the total concentration of the surfactant complex is 0.3 wt.%. The application of the above-mentioned surfactant compound system or system capable of reducing the oil-water interfacial tension to a low interfacial tension in surfactant-assisted oil displacement is also within the scope of protection of this invention.

[0022] This invention provides a surfactant compound system that reduces the interfacial tension between oil and water to a low level. The high interfacial tension is significantly reduced because the cationic groups in the amino acid-type zwitterionic surfactant form a dense adsorption film with the anionic groups of sodium dodecylbenzenesulfonate at the interface. Furthermore, temperature and salt resistance tests show that the system achieves low interfacial tension even when the NaCl solution concentration is below 2 wt.%; when the NaCl concentration is 1 wt.%, the system maintains low interfacial tension after standing at 60°C for less than 24 hours. Characterization experiments demonstrate that under certain salinity and temperature conditions, the system can maintain its superior performance in reducing the interfacial tension between oil and water to a low level. Attached Figure Description

[0023] Figure 1 The nuclear magnetic resonance C-ray spectrum of the novel amino acid surfactant TFDA prepared in Example 1 of this invention.

[0024] Figure 2 The nuclear magnetic resonance H-spectrum of the novel amino acid surfactant TFDA prepared in Example 1 of this invention.

[0025] Figure 3 The zeta potentials of the novel amino acid surfactant TFDA prepared in Example 1 of this invention at different pH values ​​are shown.

[0026] Figure 4 This is the mass spectrometry of the novel amino acid surfactant TFDA prepared in Example 1 of the present invention.

[0027] Figure 5 This is a schematic diagram of the structure and synthesis route of the amino acid surfactant TFDA, which has an isoelectric point near the pH value (6-8) of formation water, prepared in Example 1 of the present invention (taking triethylenetetramine as an example).

[0028] Figure 6 This is a performance diagram of the emulsion prepared using a surfactant compound system in Example 2 of the present invention; Figure 7 These are microscopic images of the emulsion prepared using a surfactant compound system in Example 2 of this invention; Figure 8 This is a graph showing the pH response behavior of the emulsion prepared from a surfactant compound system with pH responsive properties in Example 2 of the present invention.

[0029] Figure 9 This invention demonstrates the effect of the surfactant compound system in Embodiment 3 of reducing interfacial tension under different salinities.

[0030] Figure 10 This invention demonstrates the effect of surfactant compound system in Embodiment 3 of reducing interfacial tension under different high-temperature heating times. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0032] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0033] Example 1 This embodiment provides an amino acid-based amphoteric surfactant with an isoelectric point near the formation water pH value (6-8). The amino acid-based amphoteric surfactant includes the following steps, and the synthetic route is as follows: Figure 5 (Taking triethylenetetramine as an example) (1) Add 2.162 g of sodium lauroyl glutamate to 400 ml of deionized water and sonicate. Add 1.5 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide and 0.75 g of N-hydroxysuccinimide to the sonicated solution. Stir the solution evenly and then add 39.906 g of triethylenetetramine. (2) The above-prepared solution was ultrasonically stirred, then 5 g of sulfuric acid was added to the solution, and the pH value of the solution was adjusted to 4.7 with hydrochloric acid. The beaker was placed on a multi-point stirrer and rotated at room temperature and 450 rpm for 5 h. Then the temperature was raised to 50 °C and rotated at 450 rpm for 43 h. (3) Cool the product solution obtained from the reaction in a refrigerator at 0 ℃ for more than 5 h, then centrifuge the supernatant and pour the solid obtained from centrifugation into the turbid liquid. After centrifugation, place the turbid liquid in a refrigerator at 0 ℃ for dialysis for more than 1 day; (4) The liquid after dialysis is placed in a rotary evaporator for evaporation. After most of the volume of the solution is evaporated, it is taken out and dried by condensation to obtain the final product TFDA.

[0034] Figure 1 The nuclear magnetic resonance C-ray spectroscopy of the novel amino acid surfactant TFDA prepared is shown.

[0035] Figure 2 The nuclear magnetic resonance H-spectrum of the novel amino acid surfactant TFDA prepared in this study.

[0036] Figure 3The zeta potential of the novel amino acid surfactant TFDA at different pH values ​​was determined.

[0037] Figure 4 Mass spectrometry of the novel amino acid surfactant TFDA prepared.

[0038] Example 2 This embodiment provides the amino acid-type amphoteric surfactant TFDA prepared in Example 1 above as a stabilizer, and uses it together with sodium dodecylbenzenesulfonate to prepare a stable oil-in-water emulsion with pH responsive properties, as detailed below: Weigh 0.0435 g of the amino acid-type amphoteric surfactant TFDA and 0.0315 g of sodium dodecylbenzenesulfonate prepared in Example 1 and add them to 25 ml of 1 wt.% NaCl aqueous solution. After stirring thoroughly, adjust the pH of the solution to 4 using sodium hydroxide and dilute hydrochloric acid.

[0039] Repeat the above steps to prepare solutions with pH values ​​of 6, 8, and 10.

[0040] The above 25 ml surfactant salt solution was mixed with 10.7 ml simulated oil (crude oil and kerosene were prepared at a mass ratio of 1:2) and stirred (3000 rpm) for 5 minutes to obtain a stable oil-in-water emulsion with pH response.

[0041] The four groups of oil-in-water emulsions prepared above were placed at 25 ℃, and their emulsion stability was observed at 0 min, 5 min, 10 min, 30 min, and 60 min, respectively. The results are as follows: Figure 6 As shown, emulsions at pH 6, 8, and 10 exhibited good stability within one hour, while the group of emulsions at pH 4 experienced demulsification immediately after stirring. This indicates a significant difference in the stability of emulsions at different pH levels, indirectly verifying the pH-responsiveness of emulsions. To investigate the specific stability of emulsions at pH = 6, 8, and 10, the microstructure of the emulsions was characterized, and the results are as follows. Figure 7 As shown, since the external phase is water, the relatively large particles in the emulsion gradually aggregate towards the top. However, the microscopic images show that the emulsion aggregated at the top is dense, but the particle size is not as large as that of the emulsion at 0 min. This demonstrates that the surfactant compound system has a good emulsion stabilizing effect.

[0042] To visually demonstrate the pH-responsiveness of the emulsion, a stable emulsion with pH=7 was prepared. Diluted hydrochloric acid was then added dropwise onto the emulsion to maintain an overall pH between 4 and 5. The results are as follows. Figure 8As shown, when acid is added to a stable oil-in-water emulsion, the droplets rapidly coalesce and rise, and the precipitation of oil droplets in the emulsion system is clearly visible. After 10 minutes, the demulsification of the emulsion is basically complete, and the crude oil and aqueous phase are essentially completely separated.

[0043] Example 3 In this embodiment, the amino acid-type amphoteric surfactant TFDA prepared in Example 1 above was compounded with sodium dodecylbenzenesulfonate, and interfacial tension tests were carried out under different salinity and temperature conditions, as detailed below: 0.0435 g of the amino acid-type amphoteric surfactant TFDA and 0.0315 g of sodium dodecylbenzenesulfonate prepared in Example 1 were weighed and added to 25 ml of 1 wt.% NaCl aqueous solution. After thorough stirring, the pH of the solution was adjusted to 7 using sodium hydroxide for subsequent temperature resistance experiments with different heating times. Similarly, 0.0435 g of the amino acid-type amphoteric surfactant TFDA and 0.0315 g of sodium dodecylbenzenesulfonate prepared in Example 1 were weighed and added to 25 ml of NaCl aqueous solution (preparing 10 groups of aqueous solutions with different NaCl mass concentrations). After thorough stirring, the pH of the solution was adjusted to 7 using sodium hydroxide. The mass concentrations of the NaCl aqueous solutions were set to 0.5, 1, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 wt.%. These ten groups of aqueous solutions with different NaCl mass concentrations were subsequently used to test the interfacial tension under different salinities.

[0044] The above surfactant solution was mixed with simulated oil (crude oil and kerosene prepared at a mass ratio of 1:2) at an oil-to-water ratio of 3:7. Interfacial tension tests were then conducted under different heating durations (the above-mentioned temperature resistance test) and different salinities (the above-mentioned salt resistance test of 10 groups of mixed solutions with different salinities). The results are as follows: Figure 9 and Figure 10 As shown in the figure, the results indicate that at 25℃, the surfactant complex system with a salinity of 0.5-1 wt.% possesses the ability to reduce the oil-water interfacial tension to near-ultra-low levels. In a brine solution with a salinity of 2 wt.% or less at 25℃, the surfactant complex system can form a low interfacial tension with the simulated oil. Furthermore, within 24 hours of heating at 60℃, the interfacial tension of the surfactant complex system with a salinity of 1 wt.% NaCl remains low. These findings demonstrate that the complex system possesses certain temperature and salt tolerance. Moreover, in the salt tolerance characterization image of the complex system, the interfacial tension shows a trend of first decreasing and then increasing, indicating a synergistic effect between the surfactant complex system and the NaCl brine solution.

[0045] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. An amino acid-based amphoteric / anionic surfactant compound system, comprising an amino acid-based amphoteric surfactant and sodium dodecylbenzenesulfonate, wherein, The molar ratio of amino acid-type amphoteric surfactant to sodium dodecylbenzenesulfonate is 1:1; The amino acid-type amphoteric surfactant is prepared by an amidation reaction of lauroyl glutamic acid or its salt with triethylenetetramine. The molar ratio of lauroyl glutamic acid or its salt to triethylenetetramine is 0.01-0.02 : 0.6-0.

8.

2. The compound system according to claim 1, characterized in that, The amino acid-type amphoteric surfactant is prepared by a method comprising the following steps: 1) Sodium lauroyl glutamate was added to water and ultrasonically dispersed. Then, excess triethylenetetramine and catalysts 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide were added, and the resulting solution was ultrasonically dispersed again. 2) Adjust the reaction environment of the prepared solution, and adjust the overall pH of the solution to a slightly acidic pH of 4-5; 3) The solution was reacted under stirring. The reaction temperature was set to room temperature for the first 5 hours, and then the temperature was increased while stirring was continued to obtain the modified sodium lauroyl glutamate. 4) Allow the solution containing the product to stand at low temperature, remove the supernatant and centrifuge it, and pour the solid obtained by centrifugation into the turbid liquid; 5) The treated turbid liquid was placed in a refrigerator for dialysis. After dialysis, the liquid was evaporated to the volume of the solution to remove most of it. The solution was then freeze-dried to obtain the final product TFDA.

3. The compound system according to claim 2, characterized in that, In step 1), the molar concentration of sodium lauroyl glutamate in the resulting solution is 0.01-0.02 mol / L; The molar concentration of triethylenetetramine is 0.6-0.8 mol / L; The catalyst has a mass ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide to N-hydroxysuccinimide of 2:

1. The catalyst, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, is added at a concentration of 0.01-0.03 mol / L.

4. The compound system according to claim 2, characterized in that, In step 2), the acids used to adjust the pH are sulfuric acid and hydrochloric acid. First, sulfuric acid is added, and the remaining acid is hydrochloric acid to adjust the pH. The molar ratio of sodium lauroyl glutamate to sulfuric acid is 10:

83.

5. The compound system according to claim 2, characterized in that, In step 3), after 5 hours of reaction at room temperature, the temperature is raised to 50 °C, and then stirring is continued for 43 hours. The stirring speed is 400-600 rpm. In step 4), the temperature for the low-temperature settling is 0 ℃, and the time is 5-10 h; The centrifuge speed was 8000 rpm, and the centrifugation time was 8 minutes; In step 5), the dialysis time is greater than or equal to 1 day, and the dialysis temperature is 0 ℃.

6. The amino acid-type amphoteric / anionic surfactant compound system according to any one of claims 1-5 is used as a stabilizer to stabilize emulsions.

7. A stable oil-in-water emulsion with pH-responsive properties, prepared by a method comprising the following steps: The amino acid-type amphoteric / anionic surfactant complex system according to any one of claims 1-5 is dispersed in an aqueous NaCl salt solution, and the pH value of the prepared surfactant salt solution is adjusted to between 6 and 8. The prepared surfactant solution was used as an emulsifier and mixed with simulated oil. The mixture was stirred to obtain an oil-in-water emulsion with pH responsive properties. in, The NaCl concentration in the NaCl aqueous solution is 0.5-2 wt.%. In the surfactant salt solution, the total concentration of the surfactant complex system is 0.3 wt.%, and the molar ratio of the two surfactants is 1:

1. The oil-to-water ratio of the emulsion is 3:

7.

8. A system capable of reducing the interfacial tension between oil and water to a low level, prepared by a method comprising the following steps: The amino acid-type amphoteric / anionic surfactant complex system according to any one of claims 1-5 is dispersed in NaCl salt aqueous solution, and the pH value of the prepared surfactant salt aqueous solution is adjusted to between 6 and 8. The NaCl salt aqueous solution has a NaCl mass concentration of 0.5-2%; In the system, the total concentration of the surfactant compound system is 0.3 wt.%, and the molar ratio of the two surfactants is 1:

1.

9. The application of the amino acid-type amphoteric / anionic surfactant compound system according to any one of claims 1-5 or the system according to claim 8 capable of reducing the oil-water interfacial tension to a low interfacial tension in surfactant-assisted oil displacement.

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