Compound betaine oil-displacing agent as well as preparation method and application thereof

Abstract

The invention discloses a compound betaine oil-displacing agent as well as a preparation method and application thereof, and the compound betaine oil-displacing agent is prepared from the following components in percentage by weight: 20 to 30 percent of oleamide propyl betaine, 8 to 14 percent of coconut oil diethanolamide, 4 to 8 percent of dodecyl trimethyl ammonium chloride, 1 to 3 percent of citric acid, 0.5 to 2 percent of tetrasodium glutamate diacetate, 20 to 30 percent of organic solvent and the balance of water. And the balance of deionized water. Through the synergistic effect of oleamide propyl betaine, coconut oil diethanolamide and dodecyl trimethyl ammonium chloride, the oil displacement effect of the oil displacement agent is remarkably enhanced, and the oil displacement agent not only has good temperature resistance, salt resistance, hard water resistance and small adsorption loss on the rock surface, but also remarkably reduces the interfacial tension of oil / water, so that the oil displacement effect of the oil displacement agent is improved. And even under the condition that the use mass concentration of the oil-displacing agent is 0.02-0.05%, the oil / water interfacial tension can be reduced to 10 <-3 > mN / m order of magnitude, the use amount of the surfactant is greatly reduced, and the economic benefit is remarkably improved while the oil-displacing efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield chemical flooding, and more specifically, to a compound betaine flooding agent, a preparation method thereof, and an application thereof. Background Art

[0002] The energy problem has become a severe problem faced by China's economic development. With the continuous increase in international oil prices and the increase in the cost of exploring new oilfields, higher requirements have been put forward for improving the recovery rate of existing oilfields. Currently, the commonly used alkaline ternary composite flooding system is prone to problems such as clay detachment from the rock surface, formation of alkaline scale deposits on equipment and pipelines, corrosion of pipeline equipment, and even damage to the formation capillary structure, which has an adverse impact on tertiary oil recovery. Therefore, the alkali-free composite flooding technology has become a research hotspot.

[0003] Reducing the interfacial tension between oil and water to 10 -3 mN / m and below under alkali-free conditions poses high requirements for surfactants. Currently used traditional surfactants such as petroleum sulfonates and heavy alkylbenzene sulfonates cannot meet the requirements because it is difficult to reduce the oil-water interfacial tension of the surfactant solution to 10 -3 mN / m under alkali-free conditions, and petroleum sulfonates belong to ordinary anionic surfactants with poor hard water and salt tolerance, and a relatively high usage concentration. Betaine-type amphoteric surfactants have excellent application properties, good salt resistance, temperature resistance, low adsorption loss, emulsification properties, and compatibility, can be applied to high salinity and low permeability oil reservoirs, and have broad development prospects.

[0004] However, using a single betaine-type surfactant for oil flooding has disadvantages such as low surfactant sweep efficiency, poor oil displacement efficiency, serious adsorption loss, and high cost, especially for high-temperature and high-salinity oil reservoirs. Therefore, surfactant flooding with a composite of multiple surfactants is the general trend, using the interaction between various chemical components to improve oil recovery efficiency.

[0005] For example, Chinese Patent CN107880865A discloses a low interfacial tension foam flooding agent and a preparation method thereof. By mass percentage, the flooding agent includes the following components: 30-50% betaine, 5% dodecyl hydroxypropyl phosphate betaine, 10-25% sodium dodecyl polyoxyethylene ether sulfate, 10-15% fluorocarbon surfactant, and the balance is water; this low interfacial tension foam flooding agent has good interfacial activity and high foaming performance, has good oil displacement ability, can reduce the oil-water interfacial tension and improve the oil displacement efficiency while improving the sweep efficiency, achieving the purpose of significantly improving the recovery rate, and can effectively reduce the oil-water interfacial tension value to 10 -2 mN / m level, but has a relatively high mass concentration in the aqueous solution, which is 0.5%-1.0%.

[0006] For another example, Chinese Patent CN115418211A discloses a viscosity-reducing oil-displacing agent for heavy oil and its preparation method. The oil-displacing agent consists of the following raw materials and their mass fractions: the total mass of each raw material is 10 parts, including 1 - 2 parts of non-ionic surfactant, 2 - 3 parts of anionic surfactant, 1 - 4 parts of zwitterionic surfactant, and the balance is water; the non-ionic surfactant is fatty alcohol polyoxyethylene ether or alkylphenol polyoxyethylene ether; the anionic surfactant is fatty alcohol polyoxyethylene ether carboxylate; the zwitterionic surfactant is coconut oil amide propyl hydroxysulfobetaine and / or dodecyl dimethyl hydroxypropyl phosphate betaine; the viscosity-reducing oil-displacing agent of this invention is applicable to heavy oil reservoirs, has good viscosity-reducing effect and good compatibility with formation water, and can reduce the oil-water interfacial tension value to 10 -1 mN / m, but its effect of reducing the oil-water interfacial tension is poor.

[0007] Therefore, in actual oil production, people reasonably compound different types of surfactants with additives or different types of surfactants to reduce the oil-water interfacial tension and improve the oil recovery rate. However, in the prior art, there is still a problem that the formation of ultra-low interfacial tension is not ideal enough, and it is difficult to reduce the oil-water interfacial tension to 10 -3 mN / m and below.

[0008] In addition, Chinese Patent CN103965855A discloses a compound oil-displacing agent containing double long-chain alkyl sulfobetaine and its application. The double long-chain alkyl sulfobetaine in the compound oil-displacing agent is prepared by reacting double long-chain alkyl methyl tertiary amine with 3-chloro-2-hydroxypropyl sulfonate or 1,3-propane sultone, and it is a zwitterionic surfactant, with the number of carbon atoms in each long-chain alkyl being 8 - 18; by compounding the double long-chain alkyl sulfobetaine with a specific hydrophilic surfactant, i.e., a solubilizer, where the mole fraction of the double long-chain alkyl sulfobetaine is 0.1 - 0.7, adding 1000 mg / L of polyacrylamide to the aqueous phase, without adding any alkali or inorganic electrolyte, the interfacial tension between Daqing crude oil / formation water can be reduced to 10 -3 mN / m order of magnitude at 45°C within the range of the total surfactant concentration of 0.25 mM - 12.5 mM (mass fraction of about 0.015% - 0.75%), but the structure of its raw materials is complex and the cost is high. Summary of the Invention

[0009] Aiming at the deficiencies in the prior art, the present invention provides a compound betaine oil-displacing agent, which utilizes the synergistic effect among oleic acid amide propyl betaine, coconut diethanolamide, and dodecyl trimethyl ammonium chloride to significantly enhance the oil-displacing performance of the oil-displacing agent, so that the oil-displacing agent can reduce the oil / water interfacial tension to 10 -3 mN / m order of magnitude when used at a low mass concentration.

[0010] The present invention provides a compound betaine oil displacement agent, which is composed of the following components in weight percentages: 20-30% of oleic acid amide propyl betaine, 8-14% of coconut oil diethanolamide, 4-8% of dodecyl trimethyl ammonium chloride, 1-3% of citric acid, 0.5-2% of glutamate diacetic acid tetrasodium, 20-30% of organic solvent, and the balance being deionized water.

[0011] In the present invention, an amphoteric surfactant oleic acid amide propyl betaine, a non-ionic surfactant coconut oil diethanolamide, and a cationic surfactant dodecyl trimethyl ammonium chloride are used as the main raw materials of the oil displacement agent. By utilizing the synergistic effect among oleic acid amide propyl betaine, coconut oil diethanolamide, and dodecyl trimethyl ammonium chloride, the prepared oil displacement agent has a good oil displacement effect.

[0012] Among them, there are unsaturated bonds and amide groups in oleic acid amide propyl carboxy betaine, which can effectively reduce the interfacial tension between oil and water. At the same time, its special structure enables it to have better emulsifying and dispersing properties in the oil displacement agent system, and can form a more stable emulsion system. Moreover, the presence of the amide group in oleic acid amide propyl carboxy betaine enhances the molecular stability, making it have relatively good temperature and salt tolerance, and still can maintain good surface activity and stability in an environment with higher temperature and salt concentration; coconut oil diethanolamide mainly plays a role in thickening and stabilizing foam, can increase the viscosity of the product, enhance the persistence of foam, and can also form a micelle structure, increase the solubility of crude oil in the aqueous phase, and reduce the interfacial tension between oil and water; dodecyl trimethyl ammonium chloride has good water solubility, can quickly dissolve and ionize into an ionic state in water, can interact with negative ions on the oil / water interface, reduce the interfacial tension between oil and water, and has a certain antistatic effect.

[0013] The compounding of three surfactants, namely oleamide propyl betaine, coconut oil diethanolamide, and dodecyl trimethyl ammonium chloride, enables the surfactants to exhibit greater advantages through their interactions with each other, further enhancing the oil displacement performance. Firstly, the compounding of the three surfactants reduces the critical micelle concentration and forms a mixed adsorption layer at the oil / water interface. The molecules are arranged more closely and orderly, enhancing the surface activity and thus more effectively reducing the oil / water interfacial tension. Secondly, the amphoteric surfactant oleamide propyl carboxy betaine can combine with the cationic surfactant dodecyl trimethyl ammonium chloride through electrostatic interactions, and the non-ionic surfactant coconut oil diethanolamide inserts into the outer layer of the micelle to form a stable structure, enhancing the interfacial activity. Meanwhile, while oleamide propyl carboxy betaine and dodecyl trimethyl ammonium chloride combine through electrostatic interactions to form a stable substance, coconut oil diethanolamide can buffer the charge interactions and prevent precipitation, making the compounding system more stable. In addition, oleamide propyl carboxy betaine has good emulsifying and dispersing capabilities, which can break the crude oil into fine oil droplets. Coconut oil diethanolamide helps to stabilize the oil droplet dispersion system. Oleamide propyl carboxy betaine and coconut oil diethanolamide synergistically emulsify the crude oil to form a stable oil-in-water emulsion. Dodecyl trimethyl ammonium chloride can change the interfacial charge, enhance the dispersibility, and prevent the re-aggregation of oil droplets. The three surfactants work together to enhance the strength and elasticity of the interfacial film, improving the stability and persistence of the emulsion.

[0014] The synergistic effect of oleamide propyl betaine, coconut oil diethanolamide, and dodecyl trimethyl ammonium chloride significantly enhances the interfacial activity, emulsion stability, etc. of the oil displacement agent through charge balance, micelle structure optimization, and rheological regulation. It can more effectively reduce the oil / water interfacial tension, promote crude oil stripping, reduce the crude oil flow resistance, and improve the crude oil recovery rate and oil displacement efficiency.

[0015] Furthermore, the dosages of the three surfactants, namely oleamidopropyl betaine, coconut oil diethanolamide, and dodecyl trimethyl ammonium chloride, also need to be appropriate. Among them, oleamidopropyl betaine is 20 - 30%, coconut oil diethanolamide is 8 - 14%, and dodecyl trimethyl ammonium chloride is 4 - 8%. The synergistic effect of the three surfactants makes the performance of the compound system better, but inappropriate dosages will also lead to the opposite effect. If the dosage of oleamidopropyl betaine is too high, it may cause the intermolecular interaction to increase, forming aggregates, which is not conducive to the reduction of interfacial tension. If the dosage of dodecyl trimethyl ammonium chloride is too high, it may hinder the adsorption of other surfactants at the interface due to charge repulsion, resulting in a worse effect of reducing interfacial tension. If the dosage of coconut oil diethanolamide is too much, it may dilute the concentration of other active ingredients and weaken the overall interfacial activity. On the contrary, if the dosage of any one of the three surfactants is too low, the ideal effect of reducing the oil / water interfacial tension cannot be achieved. At the same time, the three surfactants work together to emulsify crude oil to form a stable emulsion. Inappropriate dosages may lead to too strong or too weak emulsion stability. An emulsion with too strong stability may be difficult to demulsify in the later stage of oil displacement, affecting the recovery of crude oil, while an emulsion with too weak stability is prone to demulsification and cannot effectively emulsify crude oil. Inappropriate dosages of the three surfactants will also reduce the temperature and salt resistance performance of the oil displacement agent, making it unable to maintain a stable molecular structure, resulting in a decline in performance and ineffective oil displacement.

[0016] Therefore, the appropriate dosages of the three surfactants enable them to exert the best synergistic effect, form a stable system, significantly reduce the oil / water interfacial tension, keep the emulsion stable during the oil displacement process, and be easily demulsified after production to achieve the separation of crude oil and water. They also have good temperature and salt resistance, resistance to hard water, and low adsorption loss on the rock surface. They can achieve a stable ultra-low interfacial tension in crude oil in medium-low temperature, low salinity reservoirs and high temperature and high salinity reservoirs, and have long-term stability under different reservoir conditions.

[0017] In addition, organic solvents and other additives such as citric acid and tetrasodium glutamate diacetate also play important roles in the preparation of the compound betaine oil displacement agent. Among them, the organic solvent is a co-solvent for surfactants. A suitable organic solvent can improve the solubility and dispersibility of each surfactant in the oil displacement agent system, enabling the oil displacement agent to more effectively reduce the oil / water interfacial tension and emulsify crude oil. At the same time, it can also better reduce the viscosity of crude oil and the interfacial tension between crude oil and the oil displacement agent, making it easier for crude oil and the oil displacement agent to form a miscible system and improving the oil displacement effect of the oil displacement agent. The amount of citric acid is 1-3%. Citric acid is used to adjust the pH value of the oil displacement agent. An appropriate amount enables the oil displacement agent to be in a range suitable for each surfactant to exert good effects, optimizing the performance of the oil displacement agent, enhancing its properties such as reducing the oil / water interfacial tension and emulsifying crude oil, and increasing the recovery rate of crude oil. The amount of tetrasodium glutamate diacetate is 0.5-2%. It is a chelating agent with excellent properties that can chelate metal ions in the reservoir, reduce the interference of metal ions on the components of the oil displacement agent, maintain the activity and stability of the oil displacement agent, and tetrasodium glutamate diacetate can also synergistically enhance the effect with each surfactant, effectively enhancing the adsorption of the compound system of the three surfactants at the oil / water interface and further improving the reduction effect of the oil / water interfacial tension.

[0018] The compound betaine oil displacement agent consists of the following components in weight percentages: 30% oleic acid amide propyl betaine, 8% coconut oil diethanolamide, 5% dodecyl trimethyl ammonium chloride, 2% citric acid, 1% tetrasodium glutamate diacetate, 28% organic solvent, and the balance is deionized water.

[0019] The organic solvent is selected from one of ethanol or isopropanol.

[0020] The chemical formula of oleic acid amide propyl betaine is RCONH(CH2)3N + (CH3)2CH2COO - , where R is a saturated or unsaturated mixed alkyl group with 17 carbons.

[0021] In alkyl carbon chain products, the longer the alkyl carbon chain, the stronger the hydrophobic property of the surfactant. At the oil / water interface, the hydrophobic carbon chain is more likely to penetrate into the oil phase, and the hydrophilic group remains in the water phase, forming a more stable adsorption layer, thereby more effectively reducing the oil / water interfacial tension. Therefore, oleic acid amide propyl carboxy betaine with a longer carbon chain can significantly reduce the interfacial tension at a lower concentration. And oleic acid amide propyl betaine preferably uses industrial oleic acid with a content ≥75% as the raw material, which has a wide source and low cost.

[0022] Preferably, the coconut oil diethanolamide is of the 1:1.5 type.

[0023] The coconut oil diethanolamide of 1∶1.5 type has a molar ratio of coconut oil fatty acid to diethanolamine of 1∶1.5. The performance of this coconut oil diethanolamide is more balanced, capable of forming a moderate micelle structure, having good thickening performance, foam stabilizing performance and emulsifying performance, and having good compatibility with other surfactants. When used in combination, it produces a synergistic effect, further improving the performance of the oil displacement agent.

[0024] The present invention also provides a preparation method of a compound betaine oil displacement agent. According to the weight percentages of each component, first add coconut oil diethanolamide, dodecyl trimethyl ammonium chloride, and glutamate diacetic acid tetrasodium into an organic solvent and deionized water and stir evenly, then add oleamide propyl carboxy betaine. After stirring evenly, add citric acid and stir evenly to obtain the compound betaine oil displacement agent. The temperature of the above mixing and stirring is 30 - 50 °C.

[0025] The application of the compound betaine oil displacement agent of the present invention in crude oil exploitation is that the mass concentration of the compound betaine oil displacement agent in the aqueous solution is 0.02 - 0.3%.

[0026] Furthermore, the mass concentration of the compound betaine oil displacement agent in the aqueous solution is 0.02 - 0.05%.

[0027] The compound betaine oil displacement agent of the present invention can still achieve the effect of significantly reducing the oil / water interfacial tension under the condition of a concentration lower than the conventional use concentration in crude oil exploitation.

[0028] In addition, the compound betaine oil displacement agent of the present invention makes the oil / water interfacial tension ≤ 8×10 -3 mN / m.

[0029] To sum up, the present invention prepares a compound betaine oil displacement agent by compounding three types of surfactants, namely the amphoteric surfactant oleamide propyl betaine, the non-ionic surfactant coconut oil diethanolamide, and the cationic surfactant dodecyl trimethyl ammonium chloride. By utilizing the synergistic effect between the three types of surfactants, the oil displacement effect of the oil displacement agent is significantly enhanced. It not only has good properties such as temperature and salt resistance, resistance to hard water, and small adsorption loss on the rock surface, but also significantly reduces the oil / water interfacial tension. Even when the mass concentration of the oil displacement agent is 0.02 - 0.05%, the oil / water interfacial tension can be reduced to 10 -3In the order of mN / m, it not only greatly reduces the dosage of surfactants, but also has a much better oil displacement effect than a single surfactant, significantly reducing the residual oil saturation, improving the oil displacement efficiency, and achieving a good oil displacement effect. At the same time, the compound betaine oil displacement agent prepared in the present invention does not contain alkali, can adapt to oil reservoirs under different conditions, and can achieve a stable ultra-low interfacial tension in crude oils of medium-low temperature, low salinity reservoirs and high temperature-high salinity reservoirs, and has long-term stability under different reservoir conditions. In addition, the compound betaine oil displacement agent prepared in the present invention has low raw material costs and reduced usage, greatly reducing the oil displacement cost while improving the oil displacement efficiency, and significantly improving the economic benefits. Detailed implementation manners

[0030] Embodiments of the present application will be described in more detail below. The present application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to more thoroughly and completely understand the present application. It should be understood that the embodiments of the present application are only for exemplary purposes and are not used to limit the protection scope of the present application.

[0031] Examples:

[0032] The embodiments of the present invention are implemented according to the following technical solutions. The specific steps include:

[0033] Preparation of oleic acid amide propyl carboxy betaine: The intermediate tertiary amine is synthesized by high-temperature amidation reaction of industrial oleic acid with a content of 75 wt% and N,N-1,3-dimethylpropylenediamine, and then quaternized with sodium chloroacetate in water and organic solvents.

[0034] Preparation of dodecyl trimethyl ammonium chloride: Using dodecyl tertiary amine and methyl chloride as raw materials, it is synthesized under the action of a solvent and a basic catalyst.

[0035] Preparation of coconut oil diethanolamide: It is directly amidated from coconut oil and diethanolamide under the action of a catalyst.

[0036] Preparation of the compound betaine oil displacement agent: It is composed of the following components by weight percentage: 20-30% of oleic acid amide propyl betaine, 8-14% of coconut oil diethanolamide, 4-8% of dodecyl trimethyl ammonium chloride, 1-3% of citric acid, 0.5-2% of glutamate diacetic acid tetrasodium, 20-30% of organic solvent, and the balance is made up with deionized water;

[0037] According to the weight percentages of each component, first add coconut oil diethanolamide, dodecyl trimethyl ammonium chloride, and glutamate diacetic acid tetrasodium to organic solvent and deionized water, stir evenly, then add oleamide propyl carboxy betaine, after stirring evenly, add citric acid, and after stirring evenly, the compound betaine oil displacement agent is obtained. The temperature for the above mixing and stirring is 30 - 50 °C.

[0038] Application of the compound betaine oil displacement agent in crude oil exploitation: Add water to the compound betaine oil displacement agent prepared above, and prepare chemical composite alkali-free oil displacement agents with different concentrations using produced water from the oil reservoir, with the mass percentage concentration being 0.02 - 0.30%. Use an SVT20N rotating drop tensiometer, and the test temperature is 45 °C of the simulated formation. Under this condition, measure the dynamic oil-water interfacial tension.

[0039] Table 1 shows the specific preparation conditions of the compound betaine oil displacement agent prepared in the examples of the present invention, and Table 2 shows the test results of the dynamic interfacial tension of the compound betaine oil displacement agents prepared in each example at 45 °C with different mass concentrations at 120 min.

[0040] Table 1 Specific preparation conditions of the compound betaine oil displacement agent

[0041]

[0042] Table 2 Dynamic interfacial tension of each compound betaine oil displacement agent at different mass concentration ratios at 120 min at 45 °C

[0043]

[0044] It can be seen from Table 2 that for the compound betaine oil displacement agent of the present invention, when the use mass concentration is 0.02 - 0.30%, the oil / water interfacial tension can be reduced to the order of 10 -3 mN / m, and an oil / water low interfacial tension ≤ 8×10 -3 mN / m can be obtained; when the use mass concentration of the compound betaine oil displacement agent is 0.2 - 0.3%, the reduction effect of the oil / water interfacial tension is the best, making the oil / water interfacial tension ≤ 5×10 -3 mN / m; moreover, when the use mass concentration of the compound betaine oil displacement agent is 0.02 - 0.05%, it can meet the index that the oil / water interfacial tension reaches ≤ 8×10 -3 mN / m, has good anti-dilution property, realizes the purpose of significantly reducing the oil / water interfacial tension and obtaining good oil displacement effect at a very low use concentration of the oil displacement agent, greatly reduces the use cost of the surfactant, has better applicability, and improves the economic benefit.

[0045] Meanwhile, the compound betaine oil displacement agent of the present invention has good emulsifying performance, anti-adsorption property, aging stability and oil washing efficiency. When the use mass concentration is 0.2%, its emulsifying power is 87-92% and the comprehensive emulsification index is 78-85%. After three times of adsorption, the interfacial tension is still at 4×10 -3 ~6×10 -3 mN / m. After 30 days at a constant temperature, the interfacial tension is still at 3×10 -3 ~6×10 -3 mN / m, and the oil washing efficiency is 18-23%.

[0046] In summary, the compound betaine oil displacement agent of the present invention has good oil displacement performance. In particular, the synergistic effect among amide propyl betaine oleate, coconut oil diethanolamide and dodecyl trimethyl ammonium chloride in the formula significantly enhances the oil displacement effect of the oil displacement agent. It not only has good properties such as temperature and salt resistance, anti-hard water, and small adsorption loss on the rock surface, but also has good emulsifying performance, anti-adsorption property, aging stability and oil washing efficiency. At the same time, at a low use mass concentration, it can significantly reduce the interfacial tension between oil and water, and has greater economic benefits.

[0047] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in this application, and all of them should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A compound betaine oil displacement agent, characterized in that, The compound betaine oil displacement agent is composed of the following components in weight percentages: 20-30% of oleic acid amide propyl betaine, 8-14% of coconut oil diethanolamide, 4-8% of dodecyl trimethyl ammonium chloride, 1-3% of citric acid, 0.5-2% of tetrasodium glutamate diacetate, 20-30% of organic solvent, and the balance is deionized water.

2. The compound betaine oil displacement agent according to claim 1, wherein The compound betaine oil displacement agent is composed of the following components in weight percentages: 30% of oleic acid amide propyl betaine, 8% of coconut oil diethanolamide, 5% of dodecyl trimethyl ammonium chloride, 2% of citric acid, 1% of tetrasodium glutamate diacetate, 28% of organic solvent, and the balance is deionized water.

3. A compound betaine oil displacement agent according to any one of claims 1 to 2, characterized in that The chemical formula of the above-mentioned oleamidopropyl betaine is RCONH(CH2)3N + (CH3)2CH2COO - , where R is a saturated or unsaturated mixed alkyl group with 17 carbons.

4. A compound betaine oil displacement agent according to any one of claims 1 to 2, characterized in that, The organic solvent selected is one of ethanol or isopropanol.

5. A compound betaine oil displacement agent according to any one of claims 1 to 2, characterized in that The coconut oil diethanolamide is of the 1:1.5 type.

6. The preparation method of a compound betaine oil displacement agent according to any one of claims 1 to 2, characterized in that, According to the weight percentages of the components, first add coconut oil diethanolamide, dodecyl trimethyl ammonium chloride, and tetrasodium glutamate diacetate to the organic solvent and deionized water and stir evenly, then add oleic acid amide propyl carboxy betaine, after stirring evenly add citric acid, and after stirring evenly, the compound betaine oil displacement agent is obtained. The temperature of the above mixing and stirring is 30-50 °C.

7. Use of a compound betaine oil displacement agent according to any one of claims 1 to 2 in crude oil extraction, characterized in that, The mass concentration of the compound betaine oil displacement agent in the aqueous solution is 0.02-0.30%.

8. The application of a compound betaine oil displacement agent according to claim 9 in crude oil extraction, characterized in that, The mass concentration of the compound betaine oil displacement agent in the aqueous solution is 0.02-0.05%.

9. The application of a compound betaine oil displacement agent according to claim 9 in crude oil exploitation, characterized in that, The compound betaine oil displacement agent makes the interfacial tension between oil and water ≤ 8×10 -3 mN / m.

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