A method for preparing a temperature- and salt-resistant, ultra-low interfacial tension composite oil displacement agent

Abstract

This invention discloses a method for preparing a temperature- and salt-resistant ultra-low interfacial tension composite oil displacement agent, comprising multiple steps including preparing a zwitterionic hydrophobic associating polymer, preparing a zwitterionic hydrophobic associating polymer, and preparing a zwitterionic hydrophobic associating polymer. The composite oil displacement agent prepared by this invention exhibits excellent temperature and salt resistance. The core component, the zwitterionic hydrophobic associating polymer, significantly enhances the salt resistance of the oil displacement agent by introducing a zwitterionic structure containing pyridinium cations and sulfonate anions, utilizing the electrostatic balance between ions. It can withstand high salinity of 20×10⁴~30×10⁴ mg / L. At the same time, the rigid naphthalene ring structure in the functional monomer effectively improves the thermal stability of the polymer molecular chain, enabling the oil displacement agent to retain a viscosity of ≥85% after aging at a high temperature of 120~150℃ for 72h, thus solving the problem of performance failure of traditional HPAM-type oil displacement agents under high temperature and high salt conditions.

Description

Technical Field

[0001] This invention relates to the field of oil displacement agent technology, specifically to a method for preparing a temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent. Background Technology

[0002] With the continuous reduction of recoverable reserves in conventional oil reservoirs, the development of complex reservoirs with high temperature and high salinity has become a pressing technical challenge in the current oil extraction field. In enhanced oil recovery (EOR) processes, chemical flooding is one of the core technologies for improving oil recovery. Among them, composite flooding, by combining multiple components such as polymers and surfactants, utilizes the synergistic effect to improve the oil displacement effect. Its performance is superior to single oil displacement technologies, and it has shown significant advantages in practical applications.

[0003] Currently, most industrially used composite displacement agents use partially hydrolyzed polyacrylamide (HPAM) as the core polymer component. However, HPAM's molecular chains are prone to coiling and aging at high temperatures, and the carboxyl groups on its molecular chains are sensitive to divalent metal ions such as Ca²⁺ and Mg²⁺. Under high salinity conditions, phase separation easily occurs, leading to a decrease in the viscosity of the displacement agent and a weakening of its displacement ability. This makes it difficult to meet the requirements of high temperature (≥120℃) and high salinity (≥20×10⁻⁶) conditions. 4 The oil recovery rate meets the needs of reservoirs with oil concentrations of mg / L. Meanwhile, existing composite oil displacement agents typically only reduce interfacial tension to the 10⁻²mN / m range, failing to achieve ultra-low interfacial tension (≤10⁻³mN / m). This limits their ability to strip residual oil trapped in reservoir pore throats, thus restricting further improvements in oil recovery.

[0004] Furthermore, some temperature- and salt-resistant flooding agents suffer from problems such as complex preparation processes, high costs, poor environmental performance, or insufficient component synergy, making large-scale industrial application difficult. Therefore, developing a composite flooding agent with a simple preparation process, controllable cost, and excellent temperature and salt resistance as well as ultra-low interfacial tension is of significant practical importance and application value for promoting the efficient development of complex reservoirs. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a temperature- and salt-resistant, ultra-low interfacial tension composite oil displacement agent, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a temperature- and salt-resistant ultra-low interfacial tension composite oil displacement agent, comprising the following steps: S1: Prepare zwitterionic hydrophobic associative polymer. Under nitrogen protection, intermediate 1 synthesis, functional monomer synthesis and polymerization reaction are completed sequentially to obtain zwitterionic hydrophobic associative polymer. S2: To prepare a composite surfactant system, weigh out the composite surfactant and surfactant auxiliaries according to the proportion, add them to simulated formation water, and stir at a constant temperature until completely dissolved to obtain the composite surfactant system. S3: Prepare a composite oil displacement agent. Slowly add the zwitterionic hydrophobic associative polymer prepared in S1 to the composite surfactant system obtained in step 2, stir at low speed until completely dissolved, then add the nano-reinforcing agent, and continue stirring until uniformly dispersed to obtain a temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent. The composite oil displacement agent is composed of the following raw materials in weight percentage: 0.05-0.2% zwitterionic hydrophobic associative polymer, 0.1-0.6% composite surfactant, 0.05-0.2% surfactant auxiliaries, 0.01-0.05% nano-reinforcing agent, and the balance being simulated formation water.

[0007] Preferably, the synthesis process of intermediate 1 in S1 is as follows: under nitrogen protection, sodium 3-bromopropanesulfonate, 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboryl)pyridine, potassium phosphate and tetra(triphenylphosphine)palladium are added to N,N-dimethylformamide (DMF), stirred evenly, and reacted at a constant temperature of 125-135°C for 72-96 hours. After the reaction is completed, the mixture is cooled to room temperature, filtered, DMF is recovered by vacuum distillation, and purified by recrystallization to obtain intermediate 1.

[0008] Preferably, the synthesis process of the functional monomer in S1 is as follows: under nitrogen protection, intermediate 1 and 2-bromo-3-(1-naphthyl)-1-propene are added to DMF, stirred and dissolved, and reacted at a constant temperature of 125-135°C for 72-96 hours. After the reaction is completed, the mixture is cooled to room temperature, filtered, washed with anhydrous ethanol, and dried under vacuum to obtain the functional monomer.

[0009] Preferably, the specific process of the polymerization reaction in S1 is as follows: acrylamide and functional monomers are dissolved in deionized water at a mass ratio of (12-16):(3-5), the pH of the solution is adjusted to 8.0-8.5, nitrogen gas is purged for 30-60 minutes, an initiator and a chelating agent are added, and polymerization is carried out at a constant temperature of 60-75°C for 6-12 hours. After the reaction is completed, the mixture is precipitated, filtered, vacuum dried, pulverized, and sieved to obtain a zwitterionic hydrophobic associative polymer. The initiator is a mixture of ammonium sulfate and sodium bisulfite at a mass ratio of 2:1. The chelating agent is disodium ethylenediaminetetraacetate.

[0010] Preferably, the composite surfactant in S2 is a mixture of fatty alcohol polyoxyethylene ether and sodium α-olefin sulfonate in a mass ratio of 1:1 to 2, and the surfactant auxiliary is 5-norbornene-2-carboxylic acid; the stirring conditions are 40 to 50°C, 300 to 500 r / min, and 30 to 60 min.

[0011] Preferably, the nano-reinforcing agent in S3 is nano-silica with a particle size of 20-50 nm; the stirring speed of the zwitterionic hydrophobic associative polymer is 200-300 r / min, the stirring time is 60-90 min, and the stirring time of the nano-reinforcing agent is 30-40 min.

[0012] Preferably, the salinity of the simulated formation water is 20 × 10⁻⁶. 4 ~30×10 4 mg / L, pH 7.5–8.5, which matches the actual formation environment of high-temperature and high-salinity oil reservoirs, ensuring the compatibility of the oil displacement agent with the reservoir environment.

[0013] Preferably, all reactions in S1 are carried out under nitrogen protection to prevent oxygen from interfering with the polymerization reaction, ensuring that the product has uniform molecular weight and stable performance, thereby improving the temperature and salt resistance of the oil displacement agent.

[0014] Preferably, the zwitterionic hydrophobic associating polymer in S3 needs to be added slowly to the composite surfactant system while stirring to avoid agglomeration, ensure uniform dissolution, and guarantee the synergistic effect of each component.

[0015] Preferably, the prepared composite oil displacement agent is used at 120–150°C and a salinity of 20 × 10⁻⁶. 4 ~30×10 4 After aging for 72 hours under mg / L conditions, the viscosity retention rate is ≥85% and the oil-water interfacial tension is ≤10⁻³mN / m, which can effectively improve the crude oil recovery rate by 10-15 percentage points.

[0016] Compared with the prior art, the beneficial effects of the present invention are: the composite oil displacement agent prepared by the present invention has excellent temperature and salt resistance. The core component, the zwitterionic hydrophobic associative polymer, significantly enhances the salt resistance of the oil displacement agent by introducing a zwitterionic structure containing pyridinium cations and sulfonate anions, utilizing the electrostatic balance between ions. It can withstand 20 × 10⁻⁶ ℃. 4 ~30×10 4 The high salinity of mg / L; at the same time, the rigid naphthalene ring structure in the functional monomer effectively improves the thermal stability of the polymer molecular chain, so that the viscosity retention rate of the oil displacement agent is still ≥85% after aging at a high temperature of 120-150℃ for 72h. This solves the problem of performance failure of traditional HPAM-type oil displacement agents under high temperature and high salt conditions. It also achieves ultra-low interfacial tension, improves oil displacement efficiency, has strong component synergy, stable performance, simple preparation process, and controllable cost. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] This invention provides a technical solution: a method for preparing a temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent, comprising the following steps: S1: To prepare a zwitterionic hydrophobic associative polymer, under nitrogen protection, intermediate 1 was synthesized, functional monomers were synthesized, and polymerization was carried out sequentially to obtain the zwitterionic hydrophobic associative polymer; S2: To prepare a composite surfactant system, weigh out the composite surfactant and surfactant auxiliaries according to the proportion, add them to simulated formation water, and stir at a constant temperature until completely dissolved to obtain the composite surfactant system. S3: Prepare a composite oil displacement agent. Slowly add the zwitterionic hydrophobic associative polymer prepared in S1 to the composite surfactant system obtained in step 2, stir at low speed until completely dissolved, then add the nano-reinforcing agent, and continue stirring until uniformly dispersed to obtain a temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent. The composite oil displacement agent is composed of the following raw materials in weight percentages: 0.05–0.2% zwitterionic hydrophobic associative polymer, 0.1–0.6% composite surfactant, 0.05–0.2% surfactant auxiliaries, 0.01–0.05% nano-reinforcing agent, with the balance being simulated formation water; the prepared composite oil displacement agent can withstand temperatures of 120–150℃ and a salinity of 20 × 10⁻⁶. 4 ~30×10 4 After aging for 72 hours under mg / L conditions, the viscosity retention rate is ≥85% and the oil-water interfacial tension is ≤10⁻³mN / m, which can effectively improve the crude oil recovery rate by 10-15 percentage points.

[0019] Example 1 A method for preparing a temperature- and salt-resistant, ultra-low interfacial tension composite oil displacement agent includes the following steps: S1: Preparation of zwitterionic hydrophobic associative polymers (1) Synthesis of intermediate 1: Under nitrogen protection, 1 g of sodium 3-bromopropanesulfonate, 1.8 g of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboryl)pyridine, 3.5 g of potassium phosphate and 0.2 g of tetra(triphenylphosphine)palladium were added to 50 mL of DMF. After stirring evenly, the mixture was reacted at 125 °C for 72 h. After the reaction was completed, the mixture was cooled to room temperature, filtered to remove insoluble impurities, and DMF was recovered by vacuum distillation. After recrystallization and purification, intermediate 1 was obtained. (2) Synthesis of functional monomers: Under nitrogen protection, 0.15 g of intermediate 1 and 0.35 g of 2-bromo-3-(1-naphthyl)-1-propene were added to 3 mL of DMF, stirred and dissolved, and reacted at 125 °C for 72 h. After cooling to room temperature, the mixture was filtered, washed three times with anhydrous ethanol, and dried under vacuum at 60 °C for 8 h to obtain the functional monomers. (3) Polymerization of zwitterionic hydrophobic associative polymer: 12g acrylamide and 3g functional monomer were dissolved in 78.3g deionized water, the pH of the solution was adjusted to 8.0, nitrogen gas was purged for 30min, 0.3g initiator (0.2g ammonium sulfate and 0.1g sodium bisulfite) and 0.2g chelating agent disodium ethylenediaminetetraacetate were added, and the mixture was polymerized at 60℃ for 6h. After the reaction was completed, the mixture was precipitated with anhydrous ethanol, filtered, vacuum dried at 65℃ for 12h, pulverized and passed through an 80-mesh sieve to obtain zwitterionic hydrophobic associative polymer.

[0020] S2: Preparation of composite surfactant system Weigh out 0.05g of fatty alcohol polyoxyethylene ether, 0.05g of sodium α-olefin sulfonate (total mass of composite surfactant 0.1%), and 0.05g of surfactant auxiliary 5-norbornene-2-carboxylic acid, and add 99.8g of simulated formation water (mineralization 20×10⁻⁶). 4 The composite surfactant system was obtained by stirring at 40℃ and 300r / min for 30 min in a solution of mg / L (pH 7.5) until completely dissolved.

[0021] S3: Preparation of composite oil displacement agent 0.05g of the zwitterionic hydrophobic associative polymer prepared in step 1 was slowly added to the composite surfactant system in step 2. The mixture was stirred at 200r / min for 60min until completely dissolved. Then, 0.01g of nano-silica (particle size 20nm) was added and the mixture was stirred for another 30min to obtain a temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent.

[0022] Performance testing: This oil displacement agent performed at 120℃ and a salinity of 20×10⁻⁶. 4 After aging for 72 hours under mg / L conditions, the viscosity retention rate was 85%, and the oil-water interfacial tension was 8.2 × 10⁻⁻⁻⁶. 4 mN / m, the oil recovery rate is 10 percentage points higher than that of water drive.

[0023] Example 2 A method for preparing a temperature- and salt-resistant, ultra-low interfacial tension composite oil displacement agent includes the following steps: S1: Preparation of zwitterionic hydrophobic associative polymers (1) Synthesis of intermediate 1: Under nitrogen protection, 1 g of sodium 3-bromopropanesulfonate, 1.9 g of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboryl)pyridine, 3.8 g of potassium phosphate and 0.3 g of tetra(triphenylphosphine)palladium were added to 60 mL of DMF. After stirring evenly, the mixture was reacted at 130 °C for 84 h. After the reaction was completed, the mixture was cooled to room temperature, filtered to remove insoluble impurities, and DMF was recovered by vacuum distillation. After recrystallization and purification, intermediate 1 was obtained. (2) Synthesis of functional monomers: Under nitrogen protection, 0.15 g of intermediate 1 and 0.36 g of 2-bromo-3-(1-naphthyl)-1-propene were added to 4 mL of DMF, stirred and dissolved, and reacted at 130 °C for 84 h. After cooling to room temperature, the mixture was filtered, washed 4 times with anhydrous ethanol, and dried under vacuum at 65 °C for 10 h to obtain the functional monomers. (3) Polymerization of zwitterionic hydrophobic associative polymer: 14g acrylamide and 4g functional monomer were dissolved in 81.3g deionized water, the pH of the solution was adjusted to 8.2, nitrogen gas was purged for 45min, 0.35g initiator (0.23g ammonium sulfate and 0.12g sodium bisulfite) and 0.25g chelating agent disodium ethylenediaminetetraacetate were added, and the mixture was polymerized at 68℃ for 9h. After the reaction was completed, the mixture was precipitated with anhydrous ethanol, filtered, vacuum dried at 70℃ for 18h, pulverized and passed through a 90-mesh sieve to obtain zwitterionic hydrophobic associative polymer.

[0024] S2: Preparation of composite surfactant system Weigh out 0.2g of fatty alcohol polyoxyethylene ether, 0.3g of sodium α-olefin sulfonate (total mass of composite surfactant 0.5%), and 0.15g of surfactant auxiliary 5-norbornene-2-carboxylic acid, and add 99.35g of simulated formation water (mineralization 25×10⁻⁶). 4 The composite surfactant system was obtained by stirring at 45℃ and 400r / min for 45 min in a solution of (mg / L, pH 8.0) until completely dissolved.

[0025] S3: Preparation of composite oil displacement agent 0.15g of the zwitterionic hydrophobic associative polymer prepared in step 1 was slowly added to the composite surfactant system in step 2 and stirred at 250r / min for 75min until completely dissolved. Then, 0.03g of nano silica (particle size 35nm) was added and stirred for another 35min to obtain a temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent.

[0026] Performance testing: This oil displacement agent was tested at 135℃ and a salinity of 25×10⁻⁶. 4 After aging for 72 hours under mg / L conditions, the viscosity retention rate was 88%, and the oil-water interfacial tension was 4.5 × 10⁻⁻⁻⁶. 4mN / m, the oil recovery rate is 13 percentage points higher than that of water drive.

[0027] Example 3 A method for preparing a temperature- and salt-resistant, ultra-low interfacial tension composite oil displacement agent includes the following steps: S1: Preparation of zwitterionic hydrophobic associative polymers (1) Synthesis of intermediate 1: Under nitrogen protection, 1 g of sodium 3-bromopropanesulfonate, 2.0 g of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboryl)pyridine, 4.0 g of potassium phosphate and 0.4 g of tetra(triphenylphosphine)palladium were added to 75 mL of DMF. After stirring evenly, the mixture was reacted at 135 °C for 96 h. After the reaction was completed, the mixture was cooled to room temperature, filtered to remove insoluble impurities, and DMF was recovered by vacuum distillation. After recrystallization and purification, intermediate 1 was obtained. (2) Synthesis of functional monomers: Under nitrogen protection, 0.15 g of intermediate 1 and 0.37 g of 2-bromo-3-(1-naphthyl)-1-propene were added to 5 mL of DMF, stirred and dissolved, and reacted at 135 °C for 96 h. After cooling to room temperature, the mixture was filtered, washed 5 times with anhydrous ethanol, and dried under vacuum at 70 °C for 12 h to obtain the functional monomers. (3) Polymerization of zwitterionic hydrophobic associative polymer: 16g acrylamide and 5g functional monomer were dissolved in 84.5g deionized water, the pH of the solution was adjusted to 8.5, nitrogen gas was purged for 60min, 0.4g initiator (0.27g ammonium sulfate and 0.13g sodium bisulfite) and 0.3g chelating agent disodium ethylenediaminetetraacetate were added, and the mixture was polymerized at 75℃ for 12h. After the reaction was completed, the mixture was precipitated with anhydrous ethanol, filtered, vacuum dried at 75℃ for 24h, pulverized and passed through a 100-mesh sieve to obtain zwitterionic hydrophobic associative polymer.

[0028] S2: Preparation of composite surfactant system Weigh out 0.2g of fatty alcohol polyoxyethylene ether, 0.4g of sodium α-olefin sulfonate (total mass of the composite surfactant is 0.6%), and 0.2g of surfactant auxiliary 5-norbornene-2-carboxylic acid, and add 99.0g of simulated formation water (mineralization 30×10⁻⁶). 4 The composite surfactant system was obtained by stirring at 50℃ and 500r / min for 60min in a solution of mg / L (pH 8.5) until completely dissolved.

[0029] S3: Preparation of composite oil displacement agent 0.2g of the zwitterionic hydrophobic associative polymer prepared in step 1 was slowly added to the composite surfactant system in step 2. The mixture was stirred at 300r / min for 90min until completely dissolved. Then, 0.05g of nano silica (particle size 50nm) was added and the mixture was stirred for another 40min to obtain a temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent.

[0030] Performance testing: This oil displacement agent performed at 150℃ and a salinity of 30×10⁻⁶. 4 After aging for 72 hours under the condition of mg / L, the viscosity retention rate was 90%, and the oil-water interfacial tension was 3.1×10⁻ 4 mN / m, the oil recovery rate is 15 percentage points higher than that of water drive.

[0031] Comparative experiment Using a conventional HPAM composite oil displacement agent (HPAM 0.15%, fatty alcohol polyoxyethylene ether 0.5%, water balance), under the same conditions as in Example 2 (135°C, salinity 25×10⁻⁶), the oil was removed. 4 The performance was tested using mg / L. The results showed that the viscosity retention rate of the conventional oil displacement agent after aging for 72 hours was only 42%, the oil-water interfacial tension was 2.3×10⁻²mN / m, and the crude oil recovery rate was only 4 percentage points higher than that of water flooding. This is significantly lower than that of the composite oil displacement agent prepared in this invention, indicating that the oil displacement agent of this invention has significant advantages in temperature and salt resistance and oil displacement efficiency.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a temperature- and salt-resistant, ultra-low interfacial tension composite oil displacement agent, characterized in that: Includes the following steps: S1: Prepare zwitterionic hydrophobic associative polymer. Under nitrogen protection, intermediate 1 synthesis, functional monomer synthesis and polymerization reaction are completed sequentially to obtain zwitterionic hydrophobic associative polymer. S2: To prepare a composite surfactant system, weigh out the composite surfactant and surfactant auxiliaries according to the proportion, add them to simulated formation water, and stir at a constant temperature until completely dissolved to obtain the composite surfactant system. S3: Prepare a composite oil displacement agent. Slowly add the zwitterionic hydrophobic associative polymer prepared in S1 to the composite surfactant system obtained in step 2, stir at low speed until completely dissolved, then add the nano-reinforcing agent, and continue stirring until uniformly dispersed to obtain a temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent. The composite oil displacement agent is composed of the following raw materials in weight percentage: 0.05-0.2% zwitterionic hydrophobic associative polymer, 0.1-0.6% composite surfactant, 0.05-0.2% surfactant auxiliaries, 0.01-0.05% nano-reinforcing agent, and the balance being simulated formation water.

2. The preparation method of the temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent according to claim 1, characterized in that: The synthesis process of intermediate 1 in S1 is as follows: Under nitrogen protection, sodium 3-bromopropanesulfonate, 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboryl)pyridine, potassium phosphate and tetra(triphenylphosphine)palladium are added to N,N-dimethylformamide (DMF), stirred evenly, and reacted at a constant temperature of 125-135℃ for 72-96 h. After the reaction is completed, the mixture is cooled to room temperature, filtered, DMF is recovered by vacuum distillation, and purified by recrystallization to obtain intermediate 1.

3. The preparation method of the temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent according to claim 1, characterized in that: The synthesis process of the functional monomer in S1 is as follows: Under nitrogen protection, intermediate 1 and 2-bromo-3-(1-naphthyl)-1-propene are added to DMF, stirred and dissolved, and reacted at a constant temperature of 125-135℃ for 72-96 hours. After the reaction is completed, the mixture is cooled to room temperature, filtered, washed with anhydrous ethanol, and dried under vacuum to obtain the functional monomer.

4. The preparation method of the temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent according to claim 1, characterized in that: The specific process of the polymerization reaction in S1 is as follows: Acrylamide and functional monomers are dissolved in deionized water at a mass ratio of (12-16):(3-5), the pH of the solution is adjusted to 8.0-8.5, nitrogen gas is purged for 30-60 minutes, an initiator and a chelating agent are added, and polymerization is carried out at a constant temperature of 60-75°C for 6-12 hours. After the reaction is completed, the mixture is precipitated, filtered, vacuum dried, pulverized and sieved to obtain a zwitterionic hydrophobic associative polymer. The initiator is a mixture of ammonium sulfate and sodium bisulfite at a mass ratio of 2:

1. The chelating agent is disodium ethylenediaminetetraacetate.

5. The preparation method of a temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent according to claim 1, characterized in that: The composite surfactant in S2 is a mixture of fatty alcohol polyoxyethylene ether and sodium α-olefin sulfonate in a mass ratio of 1:1 to 2, and the surfactant auxiliary is 5-norbornene-2-carboxylic acid; the stirring conditions are 40 to 50°C, 300 to 500 r / min, and 30 to 60 min.

6. The preparation method of the temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent according to claim 1, characterized in that: The nano-reinforcing agent in S3 is nano-silica with a particle size of 20-50 nm; the stirring speed of the zwitterionic hydrophobic associative polymer is 200-300 r / min, the stirring time is 60-90 min, and the stirring time of the nano-reinforcing agent is 30-40 min.

7. The preparation method of a temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent according to claim 1, characterized in that: The simulated formation water has a salinity of 20 × 10⁻⁶. 4 ~30×10 4 mg / L, pH 7.5–8.5, which matches the actual formation environment of high-temperature and high-salinity oil reservoirs, ensuring the compatibility of the oil displacement agent with the reservoir environment.

8. The preparation method of a temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent according to claim 1, characterized in that: All reactions in S1 are carried out under nitrogen protection to prevent oxygen from interfering with the polymerization reaction, ensuring that the product has uniform molecular weight and stable performance, thereby improving the temperature and salt resistance of the oil displacement agent.

9. The preparation method of a temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent according to claim 1, characterized in that: The zwitterionic hydrophobic associative polymer in S3 needs to be added slowly to the composite surfactant system while stirring to avoid agglomeration, ensure uniform dissolution, and guarantee the synergistic effect of each component.

10. The preparation method of a temperature-resistant and salt-resistant ultra-low interfacial tension composite oil displacement agent according to claim 1, characterized in that: The prepared composite oil displacement agent, at 120–150℃ and a salinity of 20 × 10⁻⁶, 4 ~30×10 4 After aging for 72 hours under mg / L conditions, the viscosity retention rate is ≥85% and the oil-water interfacial tension is ≤10⁻³mN / m, which can effectively improve the crude oil recovery rate by 10-15 percentage points.