A composite oil displacement active agent and a method for preparing the same

Abstract

The application relates to the technical field of oil field chemical oil displacement, and discloses a composite oil displacement active agent and a preparation method thereof; the preparation method is as follows: triethanolamine is added into deionized water, stirring is carried out at room temperature until complete dissolution, then fluorinated polyepoxysuccinic acid, modified erucyl zwitterionic surfactant and isopropyl alcohol are sequentially added, stirring is carried out for 1-2 hours, then modified nanosilica is added, ultrasonic treatment is carried out for 30-40 minutes, finally, sodium thiosulfate and polyether modified silicone oil are added, stirring is continuously carried out for 15-20 minutes, standing is carried out for 2-4 hours, packaging is carried out, and the composite oil displacement active agent is obtained. The composite oil displacement active agent prepared by the application has the advantages of ultralow oil-water interfacial tension, good oil displacement efficiency, permeability recovery performance and anti-swelling performance.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical flooding technology, specifically to a composite oil displacement activator and its preparation method. Background Technology

[0002] After waterflooding, a large amount of adsorbed and film-like residual crude oil remains in the formation. Conventional waterflooding has limited potential for improving oil recovery, making chemical flooding the core technology for tapping into remaining oil reserves. Currently, commonly used oil displacement surfactants are mostly single anionic surfactants, ordinary amphoteric betaines, or simple binary compound systems, which have significant shortcomings when applied to high-temperature, high-salinity, and low-permeability reservoirs. Anionic surfactants, such as petroleum sulfonates and alkylbenzene sulfonates, are prone to precipitation or phase separation under the action of high-valence metal ions, leading to increased interfacial tension. While betaine-type amphoteric surfactants offer improved salt tolerance, they lack strong anchoring groups on the rock surface, resulting in adsorption losses during migration through porous media and significantly shortening the effective contact distance. Furthermore, existing formulations often employ physical blending, lacking chemical bonding between components, making them prone to phase separation under high-temperature shear conditions. Therefore, avoiding this phenomenon is key to solving the problem. For example, patent application CN116285919A discloses a low-oil-phase residue emulsion modifier and its application method. The residue emulsion modifier provided by this invention has a simple preparation and application method, low cost, and excellent stability. It can remain stable for at least 180 days without demulsification, which significantly extends the effective period of modifier operation and is conducive to greatly improving crude oil recovery. However, its emulsification characteristics can easily lead to the inability to reduce the oil-water interfacial tension to an ultra-low level, and its permeability recovery performance and anti-swelling performance still need to be improved. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the present invention aims to provide a composite oil displacement agent and its preparation method. The composite oil displacement agent prepared by the present invention has ultra-low oil-water interfacial tension, as well as good oil displacement efficiency, permeability recovery performance and anti-swelling performance.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a composite oil displacement surfactant, comprising the following components in parts by weight: 8-12 parts by weight of modified erucic acid-based zwitterionic surfactant, 5-8 parts by weight of fluorinated polyepoxysuccinic acid, 1-2 parts by weight of modified nano-silica, 6-10 parts by weight of isopropanol, 1-3 parts by weight of triethanolamine, 0.5-1 parts by weight of sodium thiosulfate, 0.2-0.5 parts by weight of polyether-modified silicone oil, and 50-60 parts by weight of deionized water.

[0005] Furthermore, the preparation method of the modified erucic acid-based zwitterionic surfactant is as follows:

[0006] Step 1: Under nitrogen protection, add 60-70 mL of deionized water, 25-30 mL of ethanol, 2.4-2.6 g of vinylphosphonic acid, and 0.05-0.06 g of azobisisobutyronitrile to the reactor and stir until homogeneous. Then, dissolve 1.7-1.9 g of mercaptoethylamine in 14-18 mL of deionized water and add it dropwise to the reactor. After the addition is complete, stir the reaction at 60-70℃ for 4-6 h. After the reaction is complete, remove the solvent by rotary evaporation, add excess anhydrous acetone to precipitate the precipitate, filter, wash 2-3 times with anhydrous ethanol, and dry to obtain aminophosphonic acid.

[0007] Step 2: Add epichlorohydrin to the reactor, then dissolve aminophosphonic acid in a solvent prepared by mixing deionized water and isopropanol, and add it dropwise to the reactor under an ice-water bath at 0-5℃. After the addition is complete, react at 30-40℃ for 2-3 hours. Then add sodium hydroxide powder and continue to react at 30-40℃ for 2-3 hours. After the reaction is complete, distill under reduced pressure, wash and dry to obtain the phosphonic acid epoxy intermediate.

[0008] Step 3: Add erucic acid propyl dimethyl tertiary amine and phosphonic acid epoxy intermediate to anhydrous acetonitrile solvent, mix well, then add potassium iodide, and react at 70-75℃ for 5-7 hours. After the reaction is completed, distill under reduced pressure, wash with petroleum ether to remove impurities, dry, and purify to obtain modified erucic acid-based zwitterionic surfactant.

[0009] Furthermore, in step two, the ratio of epichlorohydrin, aminophosphonic acid, deionized water, isopropanol, and sodium hydroxide powder is 4.2-4.4g:1.5-1.6g:25-35mL:18-22mL:0.7-0.9g.

[0010] Furthermore, in step three, the ratio of anhydrous acetonitrile, erucamide propyl dimethyl tertiary amine, phosphonic acid epoxy intermediate, and potassium iodide is 30-40 mL: 3.8-4 g: 1.2-1.3 g: 0.03-0.04 g.

[0011] Furthermore, the preparation method of the fluorinated polyepoxysuccinic acid is as follows:

[0012] S1: Add maleic anhydride to deionized water, stir to dissolve, add 40% sodium hydroxide solution dropwise, heat to 50-60℃, then add sodium tungstate and sodium molybdate, followed by 30% hydrogen peroxide solution dropwise. After the addition, adjust the pH to 7-8 with 10% sodium hydroxide solution, cyclize at 60-70℃ for 2-3 hours. After cyclization, add 10% sodium hydroxide solution to adjust the pH to 11-12, add calcium hydroxide in 4-5 portions, and then polymerize at 80-90℃ for 2-3 hours. After the reaction is complete, cool to room temperature, adjust the pH of the solution to 2-3 with 10% hydrochloric acid, wash 2-3 times with anhydrous ethanol, and dry at 35-45℃ for 4-6 hours to obtain polyepoxysuccinic acid.

[0013] S2: Add polyepoxysuccinic acid and trifluoroethylamine to deionized water, mix well, add 10% sodium hydroxide solution to adjust the pH to 8, react at 60-70℃ for 3-4 hours, after the reaction is completed, adjust the pH of the solution to 4-5 with 10% hydrochloric acid, filter, wash and dry to obtain fluorinated polyepoxysuccinic acid.

[0014] Further, in S1, the ratio of deionized water, maleic anhydride, 40% sodium hydroxide solution, sodium tungstate, sodium molybdate, 30% hydrogen peroxide solution, and calcium hydroxide is 15-20 mL: 9.8-9.9 g: 7.5-7.6 g: 0.3-0.35 g: 0.3-0.35 g: 10-11 mL: 0.4-0.5 g.

[0015] Furthermore, the ratio of deionized water, polyepoxysuccinic acid, and trifluoroethylamine in S2 is 20-30 mL: 2.5-2.6 g: 1-1.2 g.

[0016] Further, the modified nano-silica is prepared as follows: 50-60 mL of anhydrous ethanol and 16-20 mL of deionized water are added to a reactor to prepare a solvent. Then, 2-2.2 g of nano-silica and 0.8-0.85 g of 3-aminopropyltriethoxysilane are added to the solvent. The pH of the system is adjusted to 4 with 5% hydrochloric acid. The mixture is ultrasonically treated for 40-50 min, then heated to 45-55℃ and reacted for 2-3 h. After the reaction is completed, the mixture is centrifuged for 40-50 min. The crude product is washed 2-3 times with anhydrous ethanol and vacuum dried at 55-65℃ for 22-26 h to obtain the modified nano-silica.

[0017] Further, the preparation method of the composite oil displacement agent is as follows: triethanolamine is added to deionized water and stirred at room temperature until completely dissolved. Then, fluorinated polyepoxysuccinic acid, modified erucic acid-based zwitterionic surfactant, and isopropanol are added sequentially and stirred for 1-2 hours. Next, modified nano-silica is added and ultrasonically treated for 30-40 minutes. Finally, sodium thiosulfate and polyether-modified silicone oil are added and stirred for another 15-20 minutes. The mixture is allowed to stand for 2-4 hours and then packaged to obtain the composite oil displacement agent. Attached Figure Description

[0018] Figure 1 It is the synthetic reaction formula for modified erucic acid-based zwitterionic surfactants;

[0019] Figure 2 It is the synthetic reaction formula for fluorinated polyepoxysuccinic acid;

[0020] Figure 3 This is the infrared spectrum of aminophosphonic acid;

[0021] Figure 4 This is the infrared spectrum of a phosphonic acid epoxy intermediate;

[0022] Figure 5 This is the infrared spectrum of a modified erucic acid-based zwitterionic surfactant;

[0023] Figure 6 This is the infrared spectrum of fluorinated polyepoxysuccinic acid.

[0024] Compared with the prior art, the present invention has the following beneficial technical effects:

[0025] This invention synthesizes a modified erucic acid-based zwitterionic surfactant containing phosphonic acid anchoring groups and erucic acid long-chain hydrophobic tails, and then combines it with fluorinated polyepoxysuccinic acid and amino-modified nano-silica to give the composite oil displacement surfactant of this invention excellent oil-water interfacial tension reduction and oil displacement capabilities. Among them, the modified erucic acid-based zwitterionic surfactant possesses a complete amphiphilic molecular structure composed of long hydrophobic carbon chains of erucic acid, which can be oriented at the oil-water interface, thereby achieving effective control of ultra-low interfacial tension. At the same time, the phosphonic acid chelate hydrophilic functional groups introduced into the molecule significantly reduce the adsorption loss of the surfactant on the surface of formation rocks and clay, enabling the system to maintain ultra-low interfacial tension for a long time, enhancing the emulsification and stripping ability of crude oil, and improving the recovery rate of chemical flooding. By fluorinating polyepoxysuccinic acid with trifluoroethylamine, the strong electronegativity of fluorine atoms in the grafted structure generates spatial and electrostatic repulsion, which can effectively inhibit the hydration and swelling phenomenon of clay crystal layers, fundamentally preventing reservoir pore throat blockage caused by clay hydration and swelling, and effectively maintaining the high permeability recovery value and high anti-swelling rate of the core. Meanwhile, the surface modification of nano-silica with 3-aminopropyltriethoxysilane endows the nanoparticles with good dispersion stability, avoiding their agglomeration and blockage of pore throats in high temperature and high salinity environments. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The reagents used in the following specific embodiments are of analytical grade. Additionally:

[0028] Nano-silica: Grade A380, diameter approximately 7nm, specific surface area 350m² 2 / g;

[0029] Polyether-modified silicone oil: brand name DY-ET193.

[0030] Example 1

[0031] (1) Under nitrogen protection, 60 mL of deionized water, 25 mL of ethanol, 2.4 g of vinylphosphonic acid and 0.05 g of azobisisobutyronitrile were added to the reactor and stirred evenly. Then, 1.7 g of mercaptoethylamine was dissolved in 14 mL of deionized water and added dropwise to the reactor. After the addition was complete, the reaction was stirred at 60 °C for 4 h. After the reaction was completed, the solvent was removed by rotary evaporation, excess anhydrous acetone was added to precipitate the precipitate, the precipitate was filtered, washed twice with anhydrous ethanol, and dried under vacuum at 45 °C for 12 h to obtain aminophosphonic acid.

[0032] Depend on Figure 3 It can be seen that 3500-2500 cm -1 The extremely broad and strong absorption band is attributed to the superposition of the hydrogen bond association between the phosphonic acid P-OH hydroxyl group and the stretching vibration of the amino group NH; 2930 cm⁻¹ -1 2860 cm -1 CH stretching vibration of methylene (-CH2-); 1580 cm⁻¹ -1 The vicinity is the NH bending vibration of the amino group (-NH2); 1460 cm -1 Belongs to methylene shear bending vibration; 1210 cm -1 The strong and broad absorption band is due to the stretching vibration of the phosphonic acid group P=O; 1100-900 cm⁻¹ -1 Multiple absorption bands represent the phosphonic acid fingerprint region vibrations of POH and PC bonds; 740-680 cm⁻¹ -1 The fingerprint region contains a complex absorption of PC bonds and thioether CSCs. The 1640 cm⁻¹ of the raw material vinylphosphonic acid... -1 The C=C double bond absorption band, and the 2570 cm⁻¹ band of the raw material mercaptoethylamine. -1 The SH absorption bands were not detected in the product, confirming that a click addition reaction occurred between the thiol group and the vinyl group, and the target aminophosphonic acid was successfully synthesized.

[0033] (2) Add 4.2g of epichlorohydrin to the reactor, then dissolve 1.5g of aminophosphonic acid in a solvent prepared by mixing 25mL of deionized water and 18mL of isopropanol, and add it dropwise to the reactor under an ice-water bath at 0℃. After the addition is complete, react at 30℃ for 2h, then add 0.7g of sodium hydroxide powder, and continue to react at 30℃ for 2h. After the reaction is complete, distill under reduced pressure, wash three times with ethyl acetate, and dry under vacuum at 40℃ for 8h to obtain phosphonic acid epoxy intermediate.

[0034] Depend on Figure 4 It can be seen that 3500-2600 cm -1 The broad and strong absorption bands are attributed to the hydrogen-bonded association of the hydroxyl group at the P-OH junction of phosphonic acid and the stretching vibration of the NH group in the secondary amine, and the characteristic double peaks of the primary amine -NH2 in the aminophosphonic acid precursor (~3350 / 3250 cm⁻¹). -1 The single-peak absorption of the primary amine, which has been converted to a secondary amine, indicates that the primary amine has participated in the ring-opening reaction; 2930 cm⁻¹ -1 2860 cm -1 The stretching vibration of the methylene group (CH); 1570 cm⁻¹ -1 It is a secondary amine NH bending vibration; 1460 cm -1 Belongs to methylene shear bending vibration; 1210 cm -1The strong, broad absorption band is due to the P=O stretching vibration of the phosphonic acid group; 1100-950 cm⁻¹ -1 The multiple absorption bands are fingerprint vibrations of POH and phosphonate; 910 cm⁻¹ -1 The newly appearing absorption band is a characteristic peak of the asymmetric stretching of the glycidyl ether three-membered epoxy ring COC, proving that the epoxy group has been successfully introduced; 740-680 cm⁻¹ -1 The fingerprint region contains a complex absorption of PC and CSC thioether bonds, and no obvious C-Cl residual absorption band was observed, indicating that the chlorohydrin intermediate has successfully undergone ring-closure and dechlorination to form an epoxy structure. These characteristics collectively confirm that the primary amine in the aminophosphonic acid underwent ring-opening addition with epichlorohydrin, and was successfully ring-closed by sodium hydroxide treatment, generating an epoxy-containing phosphonic acid epoxy intermediate.

[0035] (3) Add 3.8g of erucic acid propyl dimethyl tertiary amine and 1.2g of phosphonic acid epoxy intermediate to 30mL of anhydrous acetonitrile solvent, mix well, then add 0.03g of potassium iodide, react at 70℃ for 5h, after the reaction is completed, distill under reduced pressure, wash with petroleum ether to remove impurities, dry, and purify to obtain modified erucic acid-based zwitterionic surfactant.

[0036] Depend on Figure 5 It can be seen that 3500-2600 cm -1 The extremely broad and strong absorption band is attributed to the stretching vibrations of phosphonic acid P-OH and β-hydroxy OH, superimposed with the stretching vibrations of secondary amines and amides NH; 3005 cm⁻¹ -1 The weak shoulder at 2925 cm⁻¹ is due to the stretching vibration of the unsaturated double bond (=CH) in the long chain of erucic acid; -1 and 2855 cm -1 The strong absorption at 1640 cm⁻¹ is attributed to the asymmetric and symmetric stretching vibrations of the CH group of the long-chain methylene group of erucic acid; -1 and 1540 cm -1 The structure is attributed to both amide I band (C=O stretching) and amide II band (NH bending and CN stretching coupling), consistent with the starting material erucic acid amide propyl dimethyl tertiary amine, proving that the long-chain amide structure of erucic acid is intact in the product; 1220 cm -1 The strong, broad absorption band is attributed to the P=O stretching vibration of phosphonic acid, 1100-1050 cm⁻¹ -1 The broad absorption band represents the complex vibration of phosphonic acid POH and β-hydroxy CO, indicating that the phosphonic acid anchoring group remains intact during the reaction; 720 cm⁻¹ -1 The absorption band at this point is attributed to the in-plane rocking vibration of the long-chain methylene group ((CH2)). n (n≥4), further confirming the introduction of long carbon chains in erucic acid; the orthophosphonic acid epoxy intermediate is at ~910 cm -1The characteristic absorption band of epoxy COC at 740-680 cm⁻¹ was not detected in the product, indicating that the epoxy groups had been consumed by the ring-opening process of the tertiary amine; -1 The fingerprint region is a coupling absorption of the PC bond and the CSC thioether bond, which belongs to the linkage structure generated by the mercapto-alkene click reaction. Based on the reaction conditions and spectral characteristics, it can be inferred that the amide long chain (hydrophobic tail), the quaternary ammonium cation site, and the phosphonic acid anion site (zwitterionic head group) coexist in the same molecule, and the target modified erucic acid-based zwitterionic surfactant has been successfully synthesized.

[0037] (4) Add 9.8g of maleic anhydride to 15mL of deionized water, stir to dissolve, add 7.5g of 40% sodium hydroxide solution, heat to 50℃, then add 0.3g of sodium tungstate and 0.3g of sodium molybdate, then add 10mL of 30% hydrogen peroxide solution, adjust the pH to 7 with 10% sodium hydroxide solution after adding, cyclize at 60℃ for 2h, after cyclization, add 10% sodium hydroxide solution to adjust the pH to 11, add 0.4g of calcium hydroxide in 4 portions, then polymerize at 80℃ for 2h, after the reaction is complete, cool to room temperature, adjust the pH of the solution to 2 with 10% hydrochloric acid, wash twice with anhydrous ethanol, and dry at 35℃ for 4h to obtain polyepoxysuccinic acid;

[0038] (5) Add 2.5g of polyepoxysuccinic acid and 1g of trifluoroethylamine to 20mL of deionized water, mix well, add 10% sodium hydroxide solution to adjust the pH to 8, react at 60℃ for 3h, after the reaction is completed, adjust the pH of the solution to 4 with 10% hydrochloric acid, filter, wash and dry to obtain fluorinated polyepoxysuccinic acid;

[0039] Depend on Figure 6 It can be seen that 3400-3300 cm -1 The strong, broad absorption band at ~1730 cm⁻¹ is attributed to the stretching vibration of the OH group in the carboxylic acid dimer (hydrogen bond association of the carboxyl groups in the PESA backbone); -1 The region exhibits a moderately strong C=O stretching vibration in carboxylic acids (unreacted side-chain carboxyl groups), with a strength weaker than that of the starting material PESA, indicating that some carboxyl groups have participated in the reaction; ~1650 cm⁻¹ -1 and ~1550 cm -1 The newly emerging amide I band (C=O stretching) and amide II band (NH bending and CN stretching coupling) indicate that the primary amino group of trifluoroethylamine underwent a nucleophilic addition reaction with the active reactive site on the PESA molecular chain, forming a covalent amide bond; ~1350-1320 cm⁻¹ -1The newly emerging CF asymmetric stretching vibration absorption band directly proves that fluorine-containing groups have been successfully introduced into the molecular chain; ~1250-1220 cm⁻¹ -1 and ~1100 cm -1 The absorption band at this point is attributed to the stretching vibration of the COC ether bond in the PESA backbone (characteristic of polymer chains); ~970-940 cm⁻¹ -1 The spectral features indicate out-of-plane rocking vibrations of the methine groups in the PESA backbone, consistent with the unmodified PESA skeleton. These spectral characteristics confirm that fluorinated groups and amide structures were successfully introduced into the PESA molecular chain, the PESA backbone structure remained intact during the modification process, and the target fluorinated polyepoxysuccinic acid was successfully synthesized.

[0040] (6) Add 50 mL of anhydrous ethanol and 16 mL of deionized water to the reactor and mix to prepare a solvent. Then add 2 g of nano silica and 0.8 g of 3-aminopropyltriethoxysilane to it, and adjust the pH of the system to 4 with 5% hydrochloric acid. Sonicate for 40 min, then heat to 45 °C and react for 2 h. After the reaction is completed, centrifuge for 40 min, wash the crude product twice with anhydrous ethanol, and vacuum dry at 55 °C for 22 h to obtain modified nano silica.

[0041] (7) Add 1 part by weight of triethanolamine to 50 parts by weight of deionized water and stir until completely dissolved at room temperature. Then add 5 parts by weight of fluorinated polyepoxysuccinic acid, 8 parts by weight of modified erucic acid-based zwitterionic surfactant, and 6 parts by weight of isopropanol in sequence. Stir for 1 hour. Then add 1 part by weight of modified nano silica and sonicate for 30 minutes. Finally add 0.5 parts by weight of sodium thiosulfate and 0.2 parts by weight of polyether-modified silicone oil. Continue stirring for 15 minutes, let stand for 2 hours, and package to obtain the composite oil displacement agent.

[0042] Example 2

[0043] (1) Under nitrogen protection, 70 mL of deionized water, 30 mL of ethanol, 2.6 g of vinylphosphonic acid and 0.06 g of azobisisobutyronitrile were added to the reactor and stirred evenly. Then, 1.9 g of mercaptoethylamine was dissolved in 18 mL of deionized water and added dropwise to the reactor. After the addition was complete, the reaction was stirred at 70 °C for 6 h. After the reaction was completed, the solvent was removed by rotary evaporation, excess anhydrous acetone was added to precipitate the precipitate, the precipitate was filtered, washed three times with anhydrous ethanol, and dried under vacuum at 45 °C for 12 h to obtain aminophosphonic acid.

[0044] (2) Add 4.4 g of epichlorohydrin to the reactor, then dissolve 1.6 g of aminophosphonic acid in a solvent prepared by mixing 35 mL of deionized water and 22 mL of isopropanol, and add it dropwise to the reactor under an ice-water bath at 5 °C. After the addition is complete, react at 40 °C for 3 h, then add 0.9 g of sodium hydroxide powder, and continue to react at 40 °C for 3 h. After the reaction is complete, distill under reduced pressure, wash three times with ethyl acetate, and dry under vacuum at 40 °C for 8 h to obtain phosphonic acid epoxy intermediate.

[0045] (3) Add 4g of erucic acid propyl dimethyl tertiary amine and 1.3g of phosphonic acid epoxy intermediate to 40mL of anhydrous acetonitrile solvent, mix well, then add 0.04g of potassium iodide, react at 75℃ for 7h, after the reaction is completed, distill under reduced pressure, wash with petroleum ether to remove impurities, dry, and purify to obtain modified erucic acid-based zwitterionic surfactant.

[0046] (4) Add 9.9 g of maleic anhydride to 20 mL of deionized water, stir to dissolve, add 7.6 g of 40% sodium hydroxide solution, heat to 60 °C, then add 0.35 g of sodium tungstate and 0.35 g of sodium molybdate, then add 11 mL of 30% hydrogen peroxide solution, adjust the pH to 8 with 10% sodium hydroxide solution, cyclize at 70 °C for 3 h, after cyclization, add 10% sodium hydroxide solution to adjust the pH to 12, add 0.5 g of calcium hydroxide in 5 portions, then polymerize at 90 °C for 3 h, after the reaction is complete, cool to room temperature, adjust the pH of the solution to 3 with 10% hydrochloric acid, wash 3 times with anhydrous ethanol, and dry at 45 °C for 6 h to obtain polyepoxysuccinic acid;

[0047] (5) Add 2.6g of polyepoxysuccinic acid and 1.2g of trifluoroethylamine to 30mL of deionized water, mix well, add 10% sodium hydroxide solution to adjust the pH to 8, react at 70℃ for 4h, after the reaction is completed, adjust the pH of the solution to 5 with 10% hydrochloric acid, filter, wash and dry to obtain fluorinated polyepoxysuccinic acid;

[0048] (6) Add 60 mL of anhydrous ethanol and 20 mL of deionized water to the reactor and mix to prepare a solvent. Then add 2.2 g of nano silica and 0.85 g of 3-aminopropyltriethoxysilane to it, and adjust the pH of the system to 4 with 5% hydrochloric acid. Sonicate for 50 min, then heat to 55 °C and react for 3 h. After the reaction is completed, centrifuge for 50 min, wash the crude product three times with anhydrous ethanol, and vacuum dry at 65 °C for 26 h to obtain modified nano silica.

[0049] (7) Add 3 parts by weight of triethanolamine to 60 parts by weight of deionized water and stir until completely dissolved at room temperature. Then add 8 parts by weight of fluorinated polyepoxysuccinic acid, 12 parts by weight of modified erucic acid-based zwitterionic surfactant, and 10 parts by weight of isopropanol in sequence. Stir for 2 hours. Then add 2 parts by weight of modified nano-silica and sonicate for 40 minutes. Finally add 1 part by weight of sodium thiosulfate and 0.5 parts by weight of polyether-modified silicone oil. Continue stirring for 20 minutes, let stand for 4 hours, and package to obtain the composite oil displacement agent.

[0050] Example 3

[0051] (1) Under nitrogen protection, 65 mL of deionized water, 28 mL of ethanol, 2.5 g of vinylphosphonic acid and 0.05 g of azobisisobutyronitrile were added to the reactor and stirred evenly. Then, 1.8 g of mercaptoethylamine was dissolved in 16 mL of deionized water and added dropwise to the reactor. After the addition was complete, the reaction was stirred at 65 °C for 5 h. After the reaction was completed, the solvent was removed by rotary evaporation, excess anhydrous acetone was added to precipitate the precipitate, the precipitate was filtered, washed three times with anhydrous ethanol, and dried under vacuum at 45 °C for 12 h to obtain aminophosphonic acid.

[0052] (2) Add 4.3g of epichlorohydrin to the reactor, then dissolve 1.55g of aminophosphonic acid in a solvent prepared by mixing 30mL of deionized water and 20mL of isopropanol, and add it dropwise to the reactor under an ice-water bath at 2℃. After the addition is complete, react at 35℃ for 2h, then add 0.8g of sodium hydroxide powder, and continue to react at 35℃ for 2h. After the reaction is complete, distill under reduced pressure, wash with ethyl acetate 3 times, and dry under vacuum at 40℃ for 8h to obtain phosphonic acid epoxy intermediate.

[0053] (3) Add 3.9 g of erucic acid propyl dimethyl tertiary amine and 1.25 g of phosphonic acid epoxy intermediate to 35 mL of anhydrous acetonitrile solvent, mix well, then add 0.03 g of potassium iodide, react at 72 °C for 6 h, after the reaction is completed, distill under reduced pressure, wash with petroleum ether to remove impurities, dry, and purify to obtain modified erucic acid-based zwitterionic surfactant;

[0054] (4) Add 9.85g of maleic anhydride to 18mL of deionized water, stir to dissolve, add 7.55g of 40% sodium hydroxide solution, heat to 55℃, then add 0.32g of sodium tungstate and 0.32g of sodium molybdate, then add 10.5mL of 30% hydrogen peroxide solution, adjust the pH to 7 with 10% sodium hydroxide solution after adding, cyclize at 65℃ for 2h, after cyclization, add 10% sodium hydroxide solution to adjust the pH to 11, add 0.45g of calcium hydroxide in 4 portions, then polymerize at 85℃ for 3h, after the reaction is complete, cool to room temperature, adjust the pH of the solution to 2 with 10% hydrochloric acid, wash 3 times with anhydrous ethanol, and dry at 40℃ for 5h to obtain polyepoxysuccinic acid;

[0055] (5) Add 2.55g of polyepoxysuccinic acid and 1.1g of trifluoroethylamine to 25mL of deionized water, mix well, add 10% sodium hydroxide solution to adjust the pH to 8, react at 65℃ for 4h, after the reaction is completed, adjust the pH of the solution to 4 with 10% hydrochloric acid, filter, wash and dry to obtain fluorinated polyepoxysuccinic acid;

[0056] (6) Add 55 mL of anhydrous ethanol and 18 mL of deionized water to the reactor and mix to prepare a solvent. Then add 2.1 g of nano silica and 0.82 g of 3-aminopropyltriethoxysilane to it, and adjust the pH of the system to 4 with 5% hydrochloric acid. Sonicate for 45 min, then heat to 50 °C and react for 3 h. After the reaction is completed, centrifuge for 45 min, wash the crude product twice with anhydrous ethanol, and vacuum dry at 60 °C for 24 h to obtain modified nano silica.

[0057] (7) Add 2 parts by weight of triethanolamine to 55 parts by weight of deionized water and stir until completely dissolved at room temperature. Then add 6 parts by weight of fluorinated polyepoxysuccinic acid, 10 parts by weight of modified erucic acid-based zwitterionic surfactant, and 8 parts by weight of isopropanol in sequence. Stir for 1.5 h. Then add 1 part by weight of modified nano silica and sonicate for 35 min. Finally add 0.8 parts by weight of sodium thiosulfate and 0.3 parts by weight of polyether-modified silicone oil. Continue stirring for 18 min, let stand for 3 h, and package to obtain composite oil displacement agent.

[0058] Example 4

[0059] (1) Under nitrogen protection, 62 mL of deionized water, 26 mL of ethanol, 2.45 g of vinylphosphonic acid and 0.05 g of azobisisobutyronitrile were added to the reactor and stirred until homogeneous. Then, 1.75 g of mercaptoethylamine was dissolved in 15 mL of deionized water and added dropwise to the reactor. After the addition was complete, the reaction was stirred at 62 °C for 4 h. After the reaction was completed, the solvent was removed by rotary evaporation, excess anhydrous acetone was added to precipitate the precipitate, the precipitate was filtered, washed twice with anhydrous ethanol, and dried under vacuum at 45 °C for 12 h to obtain aminophosphonic acid.

[0060] (2) Add 4.25 g of epichlorohydrin to the reactor, then dissolve 1.52 g of aminophosphonic acid in a solvent prepared by mixing 28 mL of deionized water and 19 mL of isopropanol, and add it dropwise to the reactor under an ice-water bath at 1 °C. After the addition is complete, react at 32 °C for 2 h, then add 0.75 g of sodium hydroxide powder, and continue to react at 32 °C for 2 h. After the reaction is complete, distill under reduced pressure, wash three times with ethyl acetate, and dry under vacuum at 40 °C for 8 h to obtain phosphonic acid epoxy intermediate.

[0061] (3) Add 3.85g of erucic acid propyl dimethyl tertiary amine and 1.22g of phosphonic acid epoxy intermediate to 32mL of anhydrous acetonitrile solvent, mix well, then add 0.03g of potassium iodide, react at 70℃ for 5h, after the reaction is completed, distill under reduced pressure, wash with petroleum ether to remove impurities, dry, and purify to obtain modified erucic acid-based zwitterionic surfactant;

[0062] (4) Add 9.82 g of maleic anhydride to 16 mL of deionized water, stir to dissolve, add 7.53 g of 40% sodium hydroxide solution, heat to 52 °C, then add 0.31 g of sodium tungstate and 0.31 g of sodium molybdate, then add 10.5 mL of 30% hydrogen peroxide solution. After adding, adjust the pH to 7 with 10% sodium hydroxide solution. Cyclize at 60 °C for 2 h. After cyclization, add 10% sodium hydroxide solution to adjust the pH to 11. Add 0.44 g of calcium hydroxide in 4 portions, then polymerize at 82 °C for 2 h. After the reaction is complete, cool to room temperature, adjust the pH of the solution to 3 with 10% hydrochloric acid, wash 3 times with anhydrous ethanol, and dry at 38 °C for 5 h to obtain polyepoxysuccinic acid.

[0063] (5) Add 2.52g of polyepoxysuccinic acid and 1.05g of trifluoroethylamine to 22mL of deionized water, mix well, add 10% sodium hydroxide solution to adjust the pH to 8, react at 62℃ for 3h, after the reaction is completed, adjust the pH of the solution to 4 with 10% hydrochloric acid, filter, wash and dry to obtain fluorinated polyepoxysuccinic acid;

[0064] (6) Add 52 mL of anhydrous ethanol and 17 mL of deionized water to the reactor and mix to prepare a solvent. Then add 2.05 g of nano silica and 0.8 g of 3-aminopropyltriethoxysilane to it, and adjust the pH of the system to 4 with 5% hydrochloric acid. Sonicate for 42 min, then heat to 48 °C and react for 2 h. After the reaction is completed, centrifuge for 45 min, wash the crude product twice with anhydrous ethanol, and vacuum dry at 60 °C for 23 h to obtain modified nano silica.

[0065] (7) Add 1 part by weight of triethanolamine to 52 parts by weight of deionized water and stir until completely dissolved at room temperature. Then add 6 parts by weight of fluorinated polyepoxysuccinic acid, 9 parts by weight of modified erucic acid-based zwitterionic surfactant, and 7 parts by weight of isopropanol in sequence. Stir for 1 hour. Then add 1 part by weight of modified nano silica and sonicate for 35 minutes. Finally add 0.6 parts by weight of sodium thiosulfate and 0.3 parts by weight of polyether-modified silicone oil. Continue stirring for 16 minutes, let stand for 3 hours, and package to obtain the composite oil displacement agent.

[0066] Example 5

[0067] (1) Under nitrogen protection, 68 mL of deionized water, 28 mL of ethanol, 2.55 g of vinylphosphonic acid and 0.06 g of azobisisobutyronitrile were added to the reactor and stirred until homogeneous. Then, 1.85 g of mercaptoethylamine was dissolved in 17 mL of deionized water and added dropwise to the reactor. After the addition was complete, the reaction was stirred at 68 °C for 6 h. After the reaction was completed, the solvent was removed by rotary evaporation, excess anhydrous acetone was added to precipitate the precipitate, the precipitate was filtered, washed three times with anhydrous ethanol, and dried under vacuum at 45 °C for 12 h to obtain aminophosphonic acid.

[0068] (2) Add 4.35 g of epichlorohydrin to the reactor, then dissolve 1.58 g of aminophosphonic acid in a solvent prepared by mixing 32 mL of deionized water and 21 mL of isopropanol, and add it dropwise to the reactor under an ice-water bath at 5 °C. After the addition is complete, react at 40 °C for 3 h, then add 0.85 g of sodium hydroxide powder, and continue to react at 40 °C for 3 h. After the reaction is complete, distill under reduced pressure, wash three times with ethyl acetate, and dry under vacuum at 40 °C for 8 h to obtain phosphonic acid epoxy intermediate.

[0069] (3) Add 3.95g of erucic acid propyl dimethyl tertiary amine and 1.28g of phosphonic acid epoxy intermediate to 38mL of anhydrous acetonitrile solvent, mix well, then add 0.04g of potassium iodide, react at 75℃ for 7h, after the reaction is completed, distill under reduced pressure, wash with petroleum ether to remove impurities, dry, and purify to obtain modified erucic acid-based zwitterionic surfactant;

[0070] (4) Add 9.88 g of maleic anhydride to 20 mL of deionized water, stir to dissolve, add 7.58 g of 40% sodium hydroxide solution, heat to 60 °C, then add 0.34 g of sodium tungstate and 0.34 g of sodium molybdate, then add 11 mL of 30% hydrogen peroxide solution, adjust the pH to 8 with 10% sodium hydroxide solution after adding, cyclize at 70 °C for 3 h, after cyclization, add 10% sodium hydroxide solution to adjust the pH to 12, add 0.5 g of calcium hydroxide in 5 portions, then polymerize at 90 °C for 3 h, after the reaction is complete, cool to room temperature, adjust the pH of the solution to 3 with 10% hydrochloric acid, wash 3 times with anhydrous ethanol, and dry at 45 °C for 5 h to obtain polyepoxysuccinic acid;

[0071] (5) Add 2.58g of polyepoxysuccinic acid and 1.15g of trifluoroethylamine to 28mL of deionized water, mix well, add 10% sodium hydroxide solution to adjust the pH to 8, react at 68℃ for 4h, after the reaction is completed, adjust the pH of the solution to 5 with 10% hydrochloric acid, filter, wash and dry to obtain fluorinated polyepoxysuccinic acid;

[0072] (6) Add 58 mL of anhydrous ethanol and 18 mL of deionized water to the reactor and mix to prepare a solvent. Then add 2.15 g of nano silica and 0.84 g of 3-aminopropyltriethoxysilane to it, and adjust the pH of the system to 4 with 5% hydrochloric acid. Sonicate for 50 min, then heat to 55 °C and react for 3 h. After the reaction is completed, centrifuge for 50 min, wash the crude product three times with anhydrous ethanol, and vacuum dry at 60 °C for 25 h to obtain modified nano silica.

[0073] (7) Add 3 parts by weight of triethanolamine to 58 parts by weight of deionized water and stir until completely dissolved at room temperature. Then add 7 parts by weight of fluorinated polyepoxysuccinic acid, 11 parts by weight of modified erucic acid-based zwitterionic surfactant, and 9 parts by weight of isopropanol in sequence. Stir for 2 hours. Then add 2 parts by weight of modified nano-silica and sonicate for 38 minutes. Finally add 1 part by weight of sodium thiosulfate and 0.4 parts by weight of polyether-modified silicone oil. Continue stirring for 20 minutes, let stand for 4 hours, and package to obtain the composite oil displacement agent.

[0074] Comparative Example 1

[0075] The main difference between this comparative example and Example 5 is that commercially available erucamide propyl dimethyl betaine is used instead of the modified erucic acid-based zwitterionic surfactant.

[0076] Comparative Example 2

[0077] The main difference between this comparative example and Example 5 is that a phosphonic acid epoxy intermediate is used instead of a modified erucic acid-based zwitterionic surfactant.

[0078] Comparative Example 3

[0079] The main difference between this comparative example and Example 5 is that polyepoxysuccinic acid is used instead of fluorinated polyepoxysuccinic acid.

[0080] Comparative Example 4

[0081] The main difference between this comparative example and Example 5 is that nano-silica is used instead of modified nano-silica.

[0082] Performance testing

[0083] The composite oil displacement agents prepared in Examples 1-5 and Comparative Examples 1-4 were subjected to performance tests. Before the tests, each sample was prepared into a 0.3% (w / w) solution using simulated water from the target reservoir.

[0084] The simulated formation water composition was: 15,000 mg / L NaCl, 2,000 mg / L CaCl2, 1,000 mg / L MgCl2·6H2O, 1,000 mg / L Na2SO4, and 1,000 mg / L NaHCO3, with a total mineralization of 20,000 mg / L. The pH of the simulated formation water was adjusted to 7.0 ± 0.1.

[0085] A blank control group was set up simultaneously: only the same volume of simulated formation water was injected, without adding any surfactants.

[0086] (1) Interfacial tension test

[0087] The interfacial tension between the oil displacement agent solution and the simulated oil was measured using a TX500D rotating drop interfacial tensiometer at a rotation speed of 5000 r / min and a temperature of 90°C. The simulated oil was either dehydrated and degassed crude oil with a viscosity of 5 mPa·s at 90°C or a formulated simulated oil. The surfactant solution and the simulated oil were placed in a dropper and allowed to stand at a constant temperature for 30 min to equilibrate. The equilibrium interfacial tension was recorded when the fluctuation of the interfacial tension value was less than 0.001 mN / m for 5 consecutive minutes.

[0088] (2) Oil displacement efficiency test

[0089] Using the same batch of artificial sandstone cores, gas permeability was uniformly controlled between 50 and 100 mD, with a specification of Φ2.5×10 cm, and the test temperature was 90℃. After vacuuming the cores, they were saturated with simulated formation water, and the pore volume was calculated. Subsequently, simulated oil (viscosity of 5 mPa·s at 90℃) was saturated at a constant flow rate of 0.1 mL / min at 90℃ until no oil was produced at the core outlet. The initial saturated oil volume was recorded, and the cores were aged at 90℃ for 24 h. Simulated waterflooding was then performed at the same flow rate until the water cut at the outlet reached 98%. The waterflooded oil production was recorded, and the waterflood recovery rate was calculated. A test surfactant solution with a pore volume of 2 times the pore volume was injected, the valve was closed, and the cores were allowed to stand at 90℃ for 24 h. Subsequent waterflooding was performed at the same flow rate until no more oil was produced at the outlet. The chemical flooding oil production was recorded, and the total oil recovery rate was calculated.

[0090] Wherein, waterflood recovery rate (%) = (waterflooded oil production / original saturated oil volume) × 100%;

[0091] Total oil recovery (%) = (Waterflooded oil recovery + Chemicalflooded oil recovery) / Original saturated oil volume × 100%;

[0092] Chemical flooding enhances oil recovery (%) = Total oil recovery - Water flooding recovery.

[0093] The units for water-driven oil recovery and original saturated oil volume are both mL.

[0094] (3) Permeability recovery value test

[0095] Damage assessment was conducted simultaneously using the aforementioned displacement core samples, with a blank core sample (injected with simulated formation water and left to simmer for 24 hours) added as a baseline control. Simulated formation water was injected at a constant flow rate of 0.5 mL / min at 90℃. After the pressure stabilized, the displacement pressure difference was recorded, and the initial aqueous permeability K1 was calculated using Darcy's law. A solution of the active agent to be tested, five times the pore volume, was injected, the valve was closed, and the sample was kept at 90℃ for 24 hours. Simulated formation water was then injected again at the same flow rate. After the pressure stabilized, the displacement pressure difference was recorded, and the aqueous permeability K2 after damage was calculated. The permeability recovery value was calculated using the formula: Permeability recovery value (%) = K2 / K1 × 100%. The units for permeability K1 and K2 are both mD. A higher permeability recovery value indicates lower damage to the reservoir pore throat caused by the active agent.

[0096] (4) Anti-swelling rate test

[0097] A linear dilatometer was used for testing. The test temperature was 90℃. Sodium-based montmorillonite was dried at 105℃ for 2 hours, and a measured amount of dried montmorillonite powder was pressed into shape under a pressure of 10 MPa. Two parallel groups of samples were set up: a deionized water blank group (core sections were immersed in deionized water) and a test surfactant group (core sections were immersed in a 0.3% solution prepared from the example / comparative sample). The samples were kept at a constant temperature of 90℃ for 24 hours, and the clay swelling height of each group was recorded. The anti-swelling rate was calculated according to the formula: Anti-swelling rate (%) = (H0-H1) / H0×100%; where H0 is the swelling height of the deionized water blank group in mm; and H1 is the swelling height of the test surfactant group in mm.

[0098] The test results are shown in Table 1.

[0099] Table 1: Performance Tests

[0100]

[0101] As can be seen from Table 1, the composite oil displacement activator prepared in Examples 1-5 not only has ultra-low oil-water interfacial tension, but also has good oil displacement efficiency, permeability recovery performance and anti-swelling performance.

[0102] The comparison shows that Comparative Example 1, which uses commercially available erucic acid-amylamyropropyl dimethyl betaine without grafted phosphonic acid, lacks the hydrophilic functional group that chelates phosphonic acid. This significantly increases the adsorption loss of the surfactant on the surface of formation rocks and clay, making it difficult for the system to maintain ultra-low interfacial tension. The oil emulsification and stripping ability is weakened, and the chemical flooding recovery rate drops from 23.5% to 11.4%. Simultaneously, slight clay hydration intensifies, and the anti-swelling performance decreases. Comparative Example 2, which only uses a phosphonic acid epoxy intermediate, lacks the complete amphiphilic molecular structure composed of long hydrophobic carbon chains of erucic acid. It cannot be directionally distributed at the oil-water interface, completely losing the ability to regulate ultra-low interfacial tension, resulting in a significantly reduced oil recovery rate. Only 3.2% of the intermediate showed weak adsorption to the formation clay, resulting in a high permeability recovery value, but the overall oil displacement function was essentially ineffective. Comparative Example 3 used unfluorinated ordinary polyepoxysuccinic acid, which lost the strong electronegativity of fluorine atoms that repelled the clay crystal layers, significantly exacerbating clay hydration and swelling. The anti-swelling rate plummeted from 87.5% to 62.4%, and pore throat blockage caused a decrease in core permeability recovery. Comparative Example 4 used unmodified native nano-silica, whose particles easily aggregated in high-salt simulated water. The aggregated nanoparticles adsorbed some surfactants in the solution, leading to an increase in interfacial tension to 3.6 × 10⁻⁶. -3 mN / m, while the aggregates blocked the micropore throats of the low-permeability core, the permeability recovery value dropped to 62.8%, and the recovery rate dropped to 13.9%.

[0103] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0104] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0105] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. A composite oil displacement agent, characterized in that, It comprises the following components in parts by weight: 8-12 parts by weight of modified erucic acid-based zwitterionic surfactant, 5-8 parts by weight of fluorinated polyepoxysuccinic acid, 1-2 parts by weight of modified nano-silica, 6-10 parts by weight of isopropanol, 1-3 parts by weight of triethanolamine, 0.5-1 parts by weight of sodium thiosulfate, 0.2-0.5 parts by weight of polyether-modified silicone oil, and 50-60 parts by weight of deionized water.

2. The composite oil displacement agent according to claim 1, characterized in that, The preparation method of the modified erucic acid-based zwitterionic surfactant is as follows: Step 1: Under nitrogen protection, add 60-70 mL of deionized water, 25-30 mL of ethanol, 2.4-2.6 g of vinylphosphonic acid, and 0.05-0.06 g of azobisisobutyronitrile to the reactor and stir until homogeneous. Then, dissolve 1.7-1.9 g of mercaptoethylamine in 14-18 mL of deionized water and add it dropwise to the reactor. After the addition is complete, stir the reaction at 60-70℃ for 4-6 h. After the reaction is complete, remove the solvent by rotary evaporation, add excess anhydrous acetone to precipitate the precipitate, filter, wash 2-3 times with anhydrous ethanol, and dry to obtain aminophosphonic acid. Step 2: Add epichlorohydrin to the reactor, then dissolve aminophosphonic acid in a solvent prepared by mixing deionized water and isopropanol, and add it dropwise to the reactor under an ice-water bath at 0-5℃. After the addition is complete, react at 30-40℃ for 2-3 hours. Then add sodium hydroxide powder and continue to react at 30-40℃ for 2-3 hours. After the reaction is complete, distill under reduced pressure, wash and dry to obtain the phosphonic acid epoxy intermediate. Step 3: Add erucic acid propyl dimethyl tertiary amine and phosphonic acid epoxy intermediate to anhydrous acetonitrile solvent, mix well, then add potassium iodide, and react at 70-75℃ for 5-7 hours. After the reaction is completed, distill under reduced pressure, wash with petroleum ether to remove impurities, dry, and purify to obtain modified erucic acid-based zwitterionic surfactant.

3. The composite oil displacement agent according to claim 2, characterized in that, In step two, the ratio of epichlorohydrin, aminophosphonic acid, deionized water, isopropanol, and sodium hydroxide powder is 4.2-4.4g:1.5-1.6g:25-35mL:18-22mL:0.7-0.9g.

4. The composite oil displacement agent according to claim 2, characterized in that, In step three, the ratio of anhydrous acetonitrile, erucamide propyl dimethyl tertiary amine, phosphonic acid epoxy intermediate, and potassium iodide is 30-40 mL: 3.8-4 g: 1.2-1.3 g: 0.03-0.04 g.

5. The composite oil displacement agent according to claim 1, characterized in that, The preparation method of the fluorinated polyepoxysuccinic acid is as follows: S1: Add maleic anhydride to deionized water, stir to dissolve, add 40% sodium hydroxide solution dropwise, heat to 50-60℃, then add sodium tungstate and sodium molybdate, followed by 30% hydrogen peroxide solution dropwise. After the addition, adjust the pH to 7-8 with 10% sodium hydroxide solution, cyclize at 60-70℃ for 2-3 hours. After cyclization, add 10% sodium hydroxide solution to adjust the pH to 11-12, add calcium hydroxide in 4-5 portions, and then polymerize at 80-90℃ for 2-3 hours. After the reaction is complete, cool to room temperature, adjust the pH of the solution to 2-3 with 10% hydrochloric acid, wash 2-3 times with anhydrous ethanol, and dry at 35-45℃ for 4-6 hours to obtain polyepoxysuccinic acid. S2: Add polyepoxysuccinic acid and trifluoroethylamine to deionized water, mix well, add 10% sodium hydroxide solution to adjust the pH to 8, react at 60-70℃ for 3-4 hours, after the reaction is completed, adjust the pH of the solution to 4-5 with 10% hydrochloric acid, filter, wash and dry to obtain fluorinated polyepoxysuccinic acid.

6. The composite oil displacement agent according to claim 5, characterized in that, The ratio of deionized water, maleic anhydride, 40% sodium hydroxide solution, sodium tungstate, sodium molybdate, 30% hydrogen peroxide solution, and calcium hydroxide in S1 is 15-20 mL: 9.8-9.9 g: 7.5-7.6 g: 0.3-0.35 g: 0.3-0.35 g: 10-11 mL: 0.4-0.5 g.

7. The composite oil displacement agent according to claim 5, characterized in that, The ratio of deionized water, polyepoxysuccinic acid, and trifluoroethylamine in S2 is 20-30 mL: 2.5-2.6 g: 1-1.2 g.

8. The composite oil displacement agent according to claim 1, characterized in that, The modified nano-silica is prepared as follows: 50-60 mL of anhydrous ethanol and 16-20 mL of deionized water are added to a reactor to prepare a solvent. Then, 2-2.2 g of nano-silica and 0.8-0.85 g of 3-aminopropyltriethoxysilane are added to the solvent. The pH of the system is adjusted to 4 with 5% hydrochloric acid. The mixture is ultrasonically treated for 40-50 min, then heated to 45-55℃ and reacted for 2-3 h. After the reaction is completed, the mixture is centrifuged for 40-50 min. The crude product is washed 2-3 times with anhydrous ethanol and vacuum dried at 55-65℃ for 22-26 h to obtain the modified nano-silica.

9. A method for preparing the composite oil displacement agent as described in any one of claims 1-8, characterized in that, The preparation method of the composite oil displacement agent is as follows: triethanolamine is added to deionized water and stirred at room temperature until completely dissolved. Then, fluorinated polyepoxysuccinic acid, modified erucic acid-based zwitterionic surfactant, and isopropanol are added sequentially and stirred for 1-2 hours. Next, modified nano-silica is added and ultrasonically treated for 30-40 minutes. Finally, sodium thiosulfate and polyether-modified silicone oil are added and stirred for 15-20 minutes. After standing for 2-4 hours, the mixture is packaged to obtain the composite oil displacement agent.

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