Composite surfactant for oil displacement of high-salinity oil reservoir and preparation method of composite surfactant

Abstract

The invention provides a composite surfactant for oil displacement of a hypersalinity oil reservoir and a preparation method of the composite surfactant, and relates to the technical field of petrochemical engineering. The composite surfactant is prepared from the following components in percentage by weight: 0.1 to 0.3 percent of anionic-nonionic surfactant, 0.01 to 0.03 percent of cationic surfactant and the balance of formation water, wherein the anionic-nonionic surfactant is prepared by the following steps: reacting a hydroxyl-containing compound with ethylene oxide to obtain polyoxyethylene ether, then carrying out esterification modification by using aconitic acid modified rosin, then sulfonating by using a sulfonating agent, and finally neutralizing. The composite surfactant shows relatively low interfacial tension under the condition of hypersalinity (50000-200000 mg / L), is high in stability, and can be used for improving the recovery efficiency of hypersalinity oil reservoirs.

Description

Technical Field

[0001] This application relates to the field of petrochemical technology, and in particular to a composite surfactant for oil displacement in high-salinity reservoirs and its preparation method. Background Technology

[0002] Surfactants, possessing both lipophilic (hydrophobic) and hydrophilic (oleophobic) properties, disperse their molecules primarily at the oil-water interface when dissolved in water. This significantly reduces interfacial tension, meaning the surfactant system can overcome the cohesive forces between crude oil particles, thereby increasing the flow rate of crude oil through pore throats. The oil displacement effect of surfactants also manifests in reversing the wettability of lipophilic rock surfaces, emulsifying crude oil, increasing surface charge density, and promoting oil droplet coalescence.

[0003] The surfactants widely used in oilfields for enhanced oil recovery mainly include anionic and nonionic surfactants. However, single surfactants are limited by reservoir conditions and rarely achieve ideal oil recovery rates. For example, anionic surfactants (petroleum sulfonates, petroleum carboxylates, alkylbenzene sulfonates, etc.) have relatively poor interfacial activity and are not resistant to salt and salinity. Nonionic surfactants (polyoxyethylene, polyoxypropylene, etc.) can tolerate salt and poor salinity, but are not temperature resistant. Therefore, most surfactants used in tertiary oil recovery currently employ compound systems. Compounding surfactants can improve their oil recovery efficiency and enhance the temperature resistance, formation water salinity, and salt resistance of individual surfactants.

[0004] Chinese invention patent 201510683628.0 discloses a composite surfactant composition for oil displacement in medium-salinity reservoirs, consisting of anionic and cationic surfactants. This composition addresses the problem of poor oil displacement efficiency in tertiary oil recovery processes in medium-salinity reservoirs (10,000–50,000 mg / L), but it is insufficient for the development of high-salinity (above 50,000 mg / L) reservoirs. Chinese invention patent 202010939526.1 discloses a nonionic-anionic composite surfactant, its preparation method, and its application, composed of sodium octanoate and Sapindus mukorossi extract. This composite surfactant maintains good foaming performance at salinity levels of 20,000–40,000 mg / L, but its foaming performance is poor at salinity levels above 40,000 mg / L, affecting oil recovery efficiency. Chinese invention patent 202410788746.7 discloses a cationic surfactant microemulsion and its preparation method, which is made of quaternary ammonium salt cationic surfactant, fatty amine polyoxyethylene ether, alkyl pyrrolidone, isomeric alcohol ether, and water. This microemulsion has a formation water salinity tolerance of up to 90,000 mg / L, which is not suitable for higher salinity requirements. Moreover, the problem of poor formation adsorption performance of the aforementioned composite surfactant remains unresolved. Summary of the Invention

[0005] The purpose of this application is to address the shortcomings of existing technologies by providing a composite surfactant for oil displacement in high-salinity reservoirs and its preparation method. This composite surfactant can still achieve ultra-low interfacial tension in high-salinity reservoirs (50,000-200,000 mg / L), thus solving at least some of the problems existing in the prior art.

[0006] To achieve the above objectives, the technical solution adopted in this application is as follows: A composite surfactant for oil displacement in high-salinity reservoirs, by weight percentage, comprises: 0.1-0.3% anionic nonionic surfactant, 0.01-0.03% cationic surfactant, and the balance being formation water; wherein the anionic nonionic surfactant is obtained by reacting a hydroxyl-containing compound with ethylene oxide to obtain polyoxyethylene ether, and aconitine is reacted with rosin and aconitine to obtain aconitine-modified rosin, then the polyoxyethylene ether and aconitine-modified rosin undergo esterification, then a sulfonating agent is added for sulfonation, and finally neutralization is performed to obtain the final product.

[0007] Furthermore, the aconitic acid-modified rosin is prepared by an addition reaction between rosin and aconitic acid; wherein, The molar ratio of rosin to aconitic acid is 1:(1.2-2); The reaction conditions are: temperature 170-190℃, time 2-4h.

[0008] Typically, the conjugated double bonds in rosin and the double bonds in aconitic acid can undergo an addition reaction at high temperatures, generally above 150°C, and for more than 1 hour. The specific reaction temperature and time are adjusted based on the actual amount and ratio of rosin and aconitic acid used. In this application, a reaction temperature of 170-190°C and a reaction time of 2-4 hours are preferred.

[0009] Furthermore, the weight ratio of the polyoxyethylene ether to aconitic acid-modified rosin is 10:(3-5).

[0010] The anionic-nonionic surfactant of this application is a modified fatty alcohol polyoxyethylene ether sulfonate surfactant. Traditional fatty alcohol polyoxyethylene ether sulfonates combine the advantages of both anionic and nonionic surfactants and can be used in reservoirs with a salinity of less than 100,000 mg / L, but they cannot be used under higher salinity conditions. Compared with conventional fatty alcohol polyoxyethylene ether sulfonates, the surfactant of this application introduces aconitine-modified rosin. On the one hand, the carboxyl groups and other groups in aconitine-modified rosin can chelate with these metal ions to form stable chelates. This not only reduces the impact of metal ions on surfactant performance but may also improve the dispersibility and stability of surfactants in high-salinity solutions through chelate formation. Furthermore, the introduction of aconitic acid-modified rosin increases steric hindrance, hindering salt ions and other impurity particles from approaching surfactant molecules, reducing their interference with surfactant performance and thus improving salinity tolerance. Additionally, it facilitates interaction with salt ions, such as forming ion pairs with cations, which to some extent shields the electrostatic repulsion between surfactant ion head groups, making it easier for the surfactant to form micelles in salt solutions, thereby improving salt tolerance. Moreover, the combination of this anionic / nonionic surfactant with a cationic surfactant also helps improve the stability of the system, enabling it to maintain good low interfacial tension stability under long-term high-salinity reservoir conditions. However, the introduction of aconitic acid-modified rosin can affect the formation adsorption performance of the surfactant; therefore, the amount of aconitic acid-modified rosin used needs to be limited to avoid a significant decrease in the formation adsorption tolerance of the composite surfactant.

[0011] Furthermore, the hydroxyl-containing compound includes at least one dihydroxy alcohol; the dihydroxy alcohol is selected from dihydroxy alcohols having 12-16 carbon atoms, such as 1,2-dodecanediol, 1,2-hexadecanediol, etc.

[0012] This application selects dihydroxy alcohols with 12-16 carbon atoms to prepare fatty alcohol polyoxyethylene ethers, whose hydrophobic segments give them certain resistance to mineralization and salt.

[0013] In a further embodiment, the hydroxyl-containing compound further comprises 2,4-dihydroxybenzophenone; the weight ratio of the dihydroxy alcohol to 2,4-dihydroxybenzophenone is 10:(0-6), preferably 10:(1-2).

[0014] In the preparation process of polyoxyethylene ether in this application, 2,4-dihydroxybenzophenone is used to replace part of the dihydroxy alcohol. The introduction of 2,4-dihydroxybenzophenone changes the arrangement and distribution of the composite surfactant near the formation, reducing the number of polyoxyethylene ether molecules adsorbed on the formation surface per unit area, which helps to reduce the amount of formation adsorption and make up for the defects brought about by the introduction of aconitic acid modified rosin. In addition, the molecular structure of 2,4-dihydroxybenzophenone can form a more stable structure with polyoxyethylene ether, which helps to resist ion interference under high mineralization conditions and improve its mineralization resistance.

[0015] Furthermore, the sulfonating agent is selected from chlorosulfonic acid or fuming sulfuric acid.

[0016] Furthermore, the preparation method of the anionic nonionic surfactant includes the following steps: (1) Mix catalyst I with a hydroxyl-containing compound, heat to 100-150℃ under inert gas protection, add ethylene oxide to react, and obtain polyoxyethylene ether; (2) Mix the polyoxyethylene ether obtained in step (1) and aconitine-modified rosin, add catalyst II, and react at 80-90℃ for 4-6 hours to obtain esterified modified polyoxyethylene ether. (3) Mix the esterified modified polyoxyethylene ether, catalyst III and sulfonating agent, and react at 100-130℃ for 6-10h; after the reaction is complete, cool down to below 70℃, add alkali solution for neutralization, cool to room temperature, distill under reduced pressure, add ethanol to precipitate solid, filter, continue to distill under reduced pressure, and evaporate the solvent to obtain the product.

[0017] Optionally, in step (1), the molar ratio of the hydroxyl-containing compound to ethylene oxide is 1:(12-20); the reaction time is at least 0.5h, and can be 0.5h, 1h, 1.5h, 2h or even longer, depending on the amount of reactants, reaction temperature, and the type and amount of catalyst. The catalyst I is selected from at least one organic alkali metal hydroxide, sodium alkoxide, or organic amine, and is exemplary but not limited to sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide, triethylamine, etc. The amount of catalyst I is 0.1-0.5% of the total mass of the hydroxyl-containing compound and ethylene oxide.

[0018] Optionally, in step (2), the catalyst II is p-toluenesulfonic acid, and the amount of catalyst II is 0.1-3% of the total mass of the reaction raw materials.

[0019] Optionally, in step (3), the catalyst III is selected from urea and the amount used is 0.3-3% of the weight of the esterified modified polyoxyethylene ether.

[0020] Furthermore, the cationic surfactant is a quaternary ammonium salt type cationic surfactant, which contains at least one C12-C18 alkyl quaternary ammonium salt or imidazoline quaternary ammonium salt, preferably a C12-C18 alkyl quaternary ammonium salt.

[0021] Optionally, the C12-C18 alkyl quaternary ammonium salt is selected from at least one of dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, dodecyldimethylbenzylammonium chloride, and octadecyldimethylbenzylammonium chloride.

[0022] Optionally, the imidazoline-type cationic surfactant is selected from at least one of oleic acid-based imidazoline quaternary ammonium salt, benzoic acid-based imidazoline quaternary ammonium salt, naphthenic acid-based imidazoline quaternary ammonium salt, salicylic acid-based quaternary ammonium salt, or lauric acid-based imidazoline quaternary ammonium salt.

[0023] In a further embodiment, the quaternary ammonium salt-type cationic surfactant further comprises an acryloyloxyethyl alkyl quaternary ammonium salt, wherein the acryloyloxyethyl alkyl quaternary ammonium salt is selected from at least one of methacryloyloxyethyl trimethyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium bromide, methacryloyloxyethyl-dodecyl-dimethyl ammonium chloride, and methacryloyloxyethyl-dodecyl-dimethyl ammonium bromide.

[0024] Preferably, the quaternary ammonium salt-type cationic surfactant is a combination of acryloyloxyethyl alkyl quaternary ammonium salt and C12-C18 alkyl quaternary ammonium salt, wherein the proportion of acryloyloxyethyl alkyl quaternary ammonium salt is 0-30%, preferably 10-30%. That is, the proportion of acryloyloxyethyl alkyl quaternary ammonium salt in the quaternary ammonium salt-type cationic surfactant is 0-30%.

[0025] This application combines acryloyloxyethyl alkyl quaternary ammonium salt with C12-C18 alkyl quaternary ammonium salts, exhibiting a certain synergistic effect. Combined with anionic-nonionic surfactants, this helps to further improve the salinity resistance of the composite surfactant and reduce formation adsorption, enabling its use in reservoirs with a salinity of 200,000 mg / L. However, the dosage of acryloyloxyethyl alkyl quaternary ammonium salt should not be excessive to avoid increasing formation adsorption.

[0026] According to another aspect of this application, a method for preparing a composite surfactant for oil displacement in high-salinity reservoirs is provided, comprising the following steps: adding an anionic nonionic surfactant and a cationic surfactant to formation water and mixing them thoroughly to obtain the product.

[0027] Compared with the prior art, this application has the following beneficial effects: 1. This application provides a composite surfactant for oil displacement in high-salinity reservoirs. By combining anionic nonionic surfactants with quaternary ammonium salt cationic surfactants, the system exhibits low interfacial tension, stability, and good salt tolerance under high salinity conditions (50,000-200,000 mg / L), and can be used to improve oil recovery in high-salinity reservoirs.

[0028] 2. The composite surfactant for oil displacement in high-salinity reservoirs of this application, with the addition of specific anionic-nonionic surfactants, has higher resistance to salinity, formation adsorption, and stability compared with conventional anionic-nonionic surfactants.

[0029] 3. The composite surfactant for oil displacement in high-salinity reservoirs of this application combines anionic and nonionic surfactants with specific quaternary ammonium salt cationic surfactants, giving it excellent resistance to salinity and formation adsorption. Attached Figure Description

[0030] Figure 1 The infrared spectrum of the anionic nonionic surfactant in Example 1 of this application is shown.

[0031] Figure 2 This is a schematic diagram showing the 6-month long-term stability test results of the composite surfactant used for oil displacement in high-salinity reservoirs in this application. Detailed Implementation

[0032] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of this application, but do not limit this application in any way. The following content is merely an exemplary description of the scope of protection claimed in this application, and those skilled in the art can make various changes and modifications to the invention based on the disclosed content, which should also fall within the scope of protection claimed in this application.

[0033] Unless otherwise specified, all percentages in this application are by weight. In the specific embodiments described below, catalyst I is potassium hydroxide, catalyst II is p-toluenesulfonic acid, catalyst III is urea, and the sulfonating agent is chlorosulfonic acid.

[0034] The present application will be further described below by way of specific embodiments. Unless otherwise specified, all chemical reagents used in the embodiments of this application are obtained through conventional commercial means.

[0035] Example 1 A method for preparing a composite surfactant for oil displacement in high-salinity reservoirs includes the following steps: Step 1: Preparation of anionic nonionic surfactants (1) Heat rosin to melt, then add aconitine at a molar ratio of rosin to aconitine of 1:1.2, and heat to 170℃ for 4 hours to carry out an addition reaction to prepare aconitine-modified rosin; (2) Potassium hydroxide was mixed with 1,2-dodecanediol, and the mixture was heated to 100°C under inert gas protection. Ethylene oxide was added at a molar ratio of 1,2-dodecanediol to ethylene oxide of 1:12. The mixture was reacted for 2 hours to obtain polyoxyethylene ether. The amount of potassium hydroxide used was 0.1% of the total mass of 1,2-dodecanediol and ethylene oxide. (3) Mix polyoxyethylene ether and aconitic acid modified rosin at a mass ratio of 10:3, add 0.5% p-toluenesulfonic acid by weight of polyoxyethylene ether and aconitic acid modified rosin, and react at 90°C for 4 hours to obtain esterified modified polyoxyethylene ether. (4) Add chlorosulfonic acid (molar ratio of esterified polyoxyethylene ether to chlorosulfonic acid is 1:1) to the esterified modified polyoxyethylene ether and mix. Add urea at 1% of the weight of the esterified modified polyoxyethylene ether and react at 100℃ for 10 h. After the reaction is complete, cool down to below 70℃, add alkali solution for neutralization, cool to room temperature, distill under reduced pressure, add ethanol to precipitate the solid, filter, continue distilling under reduced pressure to remove the solvent, and obtain the anionic nonionic surfactant. Characterize the product by infrared spectroscopy. The results are as follows: Figure 1 As shown, the characteristic peak of COC is near 1120 cm⁻¹, the characteristic peaks of S=O are near 1070 cm⁻¹ and 1180 cm⁻¹, the characteristic peak of SO is near 612 cm⁻¹, indicating that sulfonic acid groups are introduced into the product molecule, and the characteristic peak of ester C=O is near 1730 cm⁻¹, proving that the introduction of ester groups into the product molecule, i.e., the aconitine-modified rosin, successfully esterifies polyoxyethylene ether. Step 2: Preparation of composite surfactant The mixture was prepared by adding 0.1% anionic nonionic surfactant and 0.01% cationic surfactant (dodecyltrimethylammonium chloride) to the formation water and mixing them thoroughly.

[0036] Example 2 A method for preparing a composite surfactant for oil displacement in high-salinity reservoirs includes the following steps: Step 1: Preparation of anionic nonionic surfactants (1) Heat rosin to melt, then add aconitine at a molar ratio of rosin to aconitine of 1:2, and heat to 160℃ for 5 hours to carry out an addition reaction to prepare aconitine-modified rosin; (2) Potassium hydroxide was mixed with 1,2-hexadecanediol, and the mixture was heated to 150°C under inert gas protection. Ethylene oxide was added at a molar ratio of 1,2-hexadecanediol to ethylene oxide of 1:20. The mixture was reacted for 0.5 h to obtain polyoxyethylene ether. The amount of potassium hydroxide used was 0.1% of the total mass of 1,2-hexadecanediol and ethylene oxide. (3) Mix polyoxyethylene ether and aconitine-modified rosin at a mass ratio of 10:5, add catalyst II, and react in a water bath at 90°C for 6 hours to obtain esterified modified polyoxyethylene ether. (4) Add chlorosulfonic acid (the molar ratio of esterified polyoxyethylene ether to chlorosulfonic acid is 1:1.2) to the esterified modified polyoxyethylene ether and mix. Add urea at 1% of the weight of the esterified modified polyoxyethylene ether and react at 130°C for 6 hours. After the reaction is complete, cool down to below 70°C, add alkali solution for neutralization, cool to room temperature, distill under reduced pressure, add ethanol to precipitate solid, filter, continue to distill under reduced pressure, evaporate the solvent, and obtain anionic nonionic surfactant. Step 2: Preparation of composite surfactant The mixture was prepared by adding 0.3% anionic nonionic surfactant and 0.03% cationic surfactant (octadecyl dimethyl benzyl ammonium chloride) to the formation water and mixing them thoroughly.

[0037] Example 3 The difference from Example 2 is that 1,2-hexadecanediol is replaced with 1,2-hexadecanediol and 2,4-dihydroxybenzophenone in a molar ratio of 10:1, while the total amount remains unchanged.

[0038] Example 4 The difference from Example 2 is that 1,2-hexadecanediol is replaced with 1,2-hexadecanediol and 2,4-dihydroxybenzophenone in a molar ratio of 10:2, while the total amount remains unchanged.

[0039] Example 5 The difference from Example 2 is that 1,2-hexadecanediol is replaced with 1,2-hexadecanediol and 2,4-dihydroxybenzophenone in a molar ratio of 1:3, while the total amount remains unchanged.

[0040] Example 6 The difference from Example 2 is that the cationic surfactant is replaced with octadecyl dimethyl benzyl ammonium chloride and methacryloyloxyethyl trimethyl ammonium chloride, with methacryloyloxyethyl trimethyl ammonium chloride accounting for 10%, while the total amount remains unchanged.

[0041] Example 7 The difference from Example 2 is that the cationic surfactant is replaced with octadecyl dimethyl benzyl ammonium chloride and methacryloyloxyethyl-dodecyl-dimethyl ammonium bromide, with methacryloyloxyethyl-dodecyl-dimethyl ammonium bromide accounting for 30%, while the total amount remains unchanged.

[0042] Example 8 The difference from Example 7 is that the cationic surfactant contains 50% methacryloyloxyethyl-dodecyl-dimethylammonium bromide.

[0043] Example 9 The difference from Example 7 is that the cationic surfactant is methacryloyloxyethyl-dodecyl-dimethylammonium bromide.

[0044] Comparative Example 1 The difference from Example 2 is that an equal amount of rosin was used to replace aconitic acid to modify the rosin.

[0045] Comparative Example 2 The difference from Example 2 is that an equal amount of aconitic acid is used to replace aconitic acid in the modified rosin.

[0046] Comparative Example 3 The difference from Example 2 is that, in the process of preparing the anionic nonionic surfactant, aconitine-modified rosin was not used to modify the polyoxyethylene ether.

[0047] Comparative Example 4 The difference from Example 2 is that the molar ratio of rosin to aconitine is 1:3.

[0048] Comparative Example 5 The difference from Example 2 is that the molar ratio of rosin to aconitine is 1:1.

[0049] Comparative Example 6 The difference from Example 2 is that the mass ratio of polyoxyethylene ether to aconitic acid-modified rosin is 10:6.

[0050] Test Example 1 Composite surfactants were prepared using simulated formation water with a total mineralization of 50,000-200,000 mg / L and a total calcium and magnesium ion concentration of 2,827 mg / L, respectively, according to the methods provided in the above examples and comparative examples. The oil-water interfacial tension was tested using a TX-500C rotating drop interfacial tensiometer at a test temperature of 50°C.

[0051] The test results are shown in Table 1 below.

[0052] Table 1

[0053] As shown in the table, compared to the comparative example, the composite surfactant obtained in the examples can best reduce the oil-water interfacial tension to 10 under a mineralization degree of 50,000 mg / L. -4 It has a concentration of mN / m and can form low interfacial tension even under salinity conditions of 100,000 mg / L and 200,000 mg / L, making it suitable for reservoirs with salinity of at least 50,000-200,000 mg / L.

[0054] Test Example 2 A composite surfactant was prepared using simulated formation water with a total mineralization of 200,000 mg / L and a total calcium and magnesium ion concentration of 2,827 mg / L, according to the methods provided in the above examples and comparative examples. The oil-water interfacial tension (denoted as the initial oil-water interfacial tension) was measured at 80°C. The surfactant was then encapsulated and subjected to a long-term stability thermal test in an 80°C water bath for 6 months. The oil-water interfacial tension after 6 months was then measured.

[0055] Test results are as follows Figure 2 As shown. Figure 2 Groups 1-15 correspond to Examples 1-12 and Comparative Examples 1-3, respectively, as shown in the figure. Compared with the comparative examples, the composite surfactants obtained in the examples show a smaller change in oil-water interfacial tension and better stability after long-term heat treatment.

[0056] Test Example 3 The static adsorption test mainly explores the adsorption loss of surfactant on the formation core. The test method is as follows: the composite surfactant is mixed with 80-mesh quartz sand at a ratio of 5:1, shaken at 90℃ for 24 hours, cooled and centrifuged, the supernatant is taken, and the concentration of surfactant is determined by high performance liquid chromatography (HPLC) to calculate the adsorption amount of surfactant in mg / g. The results are shown in Table 2.

[0057] Table 2

[0058] As shown in the table, compared with the comparative examples, the composite surfactants obtained in Examples 1-2 have lower static adsorption capacity and better formation adsorption resistance, thus reducing surfactant loss. Comparing Examples 1 and 2 with Comparative Examples 3-6, it can be seen that the presence of aconitic acid-modified rosin in the anionic-nonionic surface modifier can improve the adsorption resistance of the surfactant to a certain extent, but its dosage needs to be controlled to avoid excessive dosage leading to a decrease in the formation adsorption resistance of the surfactant. Furthermore, the introduction of 2,4-dihydroxybenzophenone can further enhance the formation adsorption resistance and compensate for the poor formation adsorption resistance.

[0059] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, this application is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of this application without departing from the scope of this application should be within the protection scope of this application.

Claims

1. An oil reservoir oil displacement composite surfactant, characterized by, Comprise: Anionic-nonionic surfactant 0.1-0.3%, cationic surfactant 0.01-0.03%, the rest is formation water; wherein, The anionic-nonionic surfactant is obtained by reacting a hydroxyl-containing compound and ethylene oxide to obtain a polyoxyethylene ether, then a rosin and aconitic acid are subjected to an addition reaction to obtain a rosin modified with aconitic acid, then the polyoxyethylene ether and the rosin modified with aconitic acid are subjected to an esterification reaction, and then a sulfonating agent is added to perform a sulfonation reaction; the molar ratio of the rosin to the aconitic acid is 1:(1.2-2); the weight ratio of the polyoxyethylene ether to the rosin modified with aconitic acid is 10:(3-5); The cationic surfactant is a quaternary ammonium salt type cationic surfactant; the hydroxyl-containing compound comprises at least one binary fatty alcohol; and the sulfonating agent is selected from chlorosulfonic acid or oleum.

2. The oil reservoir flooding composite surfactant according to claim 1, characterized by, The binary fatty alcohol is selected from binary fatty alcohols with carbon atom numbers of 12-16.

3. The oil reservoir flooding composite surfactant according to claim 1, characterized by, The hydroxyl-containing compound further comprises 2,4-dihydroxybenzophenone.

4. The oil reservoir oil displacement composite surfactant according to claim 3, characterized by, The weight ratio of the binary fatty alcohol to the 2,4-dihydroxybenzophenone is 10:(0-6).

5. The oil reservoir flooding composite surfactant according to claim 1, characterized in that, The preparation method of the anionic-nonionic surfactant comprises the following steps: (1) mixing a catalyst I and a hydroxyl-containing compound, under the protection of inert gas, heating to 100-150 DEG C, adding ethylene oxide to perform a reaction, and obtaining a polyoxyethylene ether; (2) mixing the polyoxyethylene ether obtained in step (1) and a rosin modified with aconitic acid, adding a catalyst II, and reacting at 80-90 DEG C for 4-6 h to obtain an esterification modified polyoxyethylene ether; (3) mixing the esterification modified polyoxyethylene ether, a catalyst III and a sulfonating agent, reacting at 100-130 DEG C for 6-10 h; after the reaction is completed, cooling to below 70 DEG C, adding a lye to perform neutralization, cooling to room temperature, vacuum distillation, adding ethanol to precipitate a solid, filtering, continuing vacuum distillation, and distilling off the solvent to obtain the product.

6. The oil reservoir flooding composite surfactant according to claim 5, characterized in that, The molar ratio of the hydroxyl-containing compound to ethylene oxide is 1:(12-20).

7. The oil reservoir flooding composite surfactant according to claim 1, characterized in that, The quaternary ammonium salt type cationic surfactant comprises at least one C12-C18 alkyl quaternary ammonium salt and imidazoline amide quaternary ammonium salt.

8. The oil reservoir flooding composite surfactant according to claim 7, characterized in that, The quaternary ammonium salt type cationic surfactant further comprises a propenoyloxyethyl alkyl quaternary ammonium salt, which is selected from at least one of methyl propenoyloxyethyl trimethyl ammonium chloride, methyl propenoyloxyethyl trimethyl ammonium bromide, methyl propenoyloxyethyl-dodecyl-dimethyl ammonium chloride and methyl propenoyloxyethyl-dodecyl-dimethyl ammonium bromide.

9. The oil reservoir oil displacement composite surfactant according to claim 8, characterized by, The quaternary ammonium salt type cationic surfactant is a combination of the propenoyloxyethyl alkyl quaternary ammonium salt and the C12-C18 alkyl quaternary ammonium salt, wherein the proportion of the propenoyloxyethyl alkyl quaternary ammonium salt is 0-30%.

10. The method of preparing a complex surfactant for enhanced oil recovery according to any one of claims 1 to 9, characterized in that, The preparation method comprises the following steps: dissolving the anionic-nonionic surfactant and the cationic surfactant in water respectively, and then uniformly mixing them to obtain the product.

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