Temperature-resistant salt-resistant oil displacement polymer and preparation method thereof

Abstract

The invention discloses a temperature-resistant and salt-resistant polymer for oil displacement and a preparation method thereof.The preparation method comprises the steps that acrylamide, sodium acrylate, a vinyl monomer, an N, N-diallyl-n-alkylaniline monomer and a cosolvent are dissolved in deionized water to obtain a reaction solution, and the PH value of the reaction solution is adjusted to 8-12; under the protection of nitrogen, an initiator is added into the reaction liquid, and a polymerization reaction product of the reaction liquid is the temperature-resistant and salt-resistant polymer for oil displacement; the problems that an existing temperature-resistant and salt-resistant oil displacement polymer is single in structural characteristic, the long-term stability requirement of the polymer under the high-temperature and high-salinity use condition is difficult to meet, and the solubility of the polymer is reduced after a long-chain branch and a cross-linked structure are introduced are effectively solved.

Description

Technical Field

[0001] This disclosure relates to polymers for tertiary oil recovery in oilfields, specifically to the synthesis of temperature-resistant and salt-resistant oil displacement agents suitable for high-temperature and high-salt conditions. Background Technology

[0002] Currently, the formation conditions for polymer flooding are gradually transitioning from low-temperature, low-salinity to high-temperature, high-salinity conditions. Especially with the expansion of oilfield exploration and development into offshore areas, improving recovery rates under such harsh formation conditions is a major challenge in the field of chemical flooding research. Commonly used flooding polymers are mainly partially hydrolyzed polyacrylamide (HPAM) and its derivatives. HPAM is highly hydrophilic, readily forming hydrogen bonds with water, and easily soluble in water. After hydration, it has a large hydrodynamic volume, thus acting as a thickener. However, due to its flexible molecular chains, it exhibits a random coil conformation in aqueous solutions. In high-temperature (the operating temperature of ordinary HPAM generally does not exceed 90℃) and high-salinity brine, the molecular chains coil, resulting in a significant decrease in viscosity and a marked loss of the polymer solution's thickening effect. Furthermore, the flexible chains are prone to mechanical degradation, significantly limiting its application range and failing to adequately meet the requirements of high-temperature, high-salinity formation flooding. With the deepening of crude oil extraction, the scope of tertiary oil recovery has gradually expanded to high-temperature, high-salinity reservoirs. The relatively harsh geological conditions place higher demands on the temperature and salt resistance of polymers. The demand for polymer flooding agents that are adapted to high-temperature and high-salinity reservoir conditions is also increasing year by year.

[0003] Current research directions for improving the temperature and salt resistance of polymers mainly fall into three categories: First, synthesizing non-associative AM polymers with temperature and salt resistance structural units. This involves introducing functional structural units into the PAM molecular chain that inhibit hydrolysis, can complex high-valent cations, have strong hydration capabilities, and increase the rigidity of the polymer chain to prepare high-performance polymer flooding agents. However, while introducing such structural units can increase the temperature resistance of polymers, it cannot overcome the thickening properties of polymers at high salinity. Specifically, the initial viscosity of polymers is often low under high temperature and high salinity conditions, and even if the viscosity retention rate is high, it cannot meet the application requirements. Second, synthesizing polymer flooding agents with special interactions, such as hydrophobic associative polymers, molecular complex flooding agents, zwitterionic polymers, and colloidal dispersion gels. These polymers can overcome the problem of low initial viscosity, but they require high solution concentrations to achieve good temperature and salt resistance, resulting in high usage costs. Third, preparing mildly cross-linked polymers. The presence of cross-linked structures can enhance polymer rigidity, increase the difficulty of conformational transformation, improve salt resistance, and enhance thickening properties. However, the use of cross-linking agents often leads to decreased polymer solubility, reduced injection performance, and limited application conditions. Therefore, currently synthesized heat- and salt-resistant oil displacement polymers often suffer from limited structural characteristics and cannot meet the long-term stability requirements under high-temperature and high-salinity application conditions. Summary of the Invention

[0004] In view of this, this disclosure provides a heat-resistant and salt-resistant flooding polymer and its preparation method, which solves the problem that the current heat-resistant and salt-resistant flooding polymers have simple structural characteristics, making it difficult to meet the long-term stability requirements of polymers under high temperature and high salinity conditions, and that the solubility of polymers decreases after the introduction of long-branched and cross-linked structures.

[0005] Firstly, the polymer for temperature-resistant and salt-resistant oil displacement described in this disclosure has the following molecular structural formula:

[0006]

[0007] Where: a, b, and c correspond to the molar percentage of structural units in the total units, a is 76%–79%, b is 7%–9%, ​​c is 8%–10%, and d is 100%–abc; n = 11, 13, 15; R1 is selected from the following groups:

[0008]

[0009] Secondly, the preparation method of the temperature-resistant and salt-resistant oil displacement polymer described in this disclosure includes:

[0010] Acrylamide, sodium acrylate, vinyl monomer, N,N-diallyl-nalkylaniline monomer and cosolvent are dissolved in deionized water to obtain a reaction solution, and the pH value of the reaction solution is adjusted to 8-12; under nitrogen protection, an initiator is added to the reaction solution, and the product of the polymerization reaction is the heat-resistant and salt-resistant oil displacement polymer.

[0011] In this disclosure and possible embodiments, the vinyl monomer is vinylpyrrolidone, sodium p-styrenesulfonate, or sodium 2-acrylamido-2-methylpropanesulfonate.

[0012] In this disclosure and possible embodiments, the co-solvent is one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and octylphenol polyoxyethylene ether, and the amount of the co-solvent is 0.08% to 0.2% of the total mass of the reaction raw materials.

[0013] In this disclosure and possible embodiments, the initiator is composed of an azo initiator and a redox initiator.

[0014] In this disclosure and possible embodiments, the azo initiator is at least one of azobisisobutyramidine hydrochloride, azobisisopropylimidazoline hydrochloride, and azobisisobutyronitrile, and the amount of the azo initiator is 0.005% to 0.015% of the total mass of the reaction raw materials;

[0015] The oxidant in the redox initiator is one or more of hydrogen peroxide, cumene hydrogen peroxide, ammonium persulfate, and benzoyl peroxide; the reducing agent is one or more of sodium bisulfite, sodium sulfate, and sodium metabisulfite; the amount of the oxidant is 0.01% to 0.03% of the total mass of the reaction raw materials, and the amount of the reducing agent is 0.02% to 0.04% of the total mass of the reaction raw materials.

[0016] In this disclosure and possible embodiments, the polymerization reaction time is 8 to 12 hours.

[0017] In this disclosure and possible embodiments, the polymerization reaction occurs in the reaction solution in a reactor. Under nitrogen protection, the temperature of the reactor is controlled at 5–20°C, and the initiator is added 15–20 minutes after nitrogen is introduced.

[0018] In this disclosure and possible embodiments, the polymerization reaction is completed to obtain a polymer colloid; the polymer colloid is dried and then pulverized to obtain the heat-resistant and salt-resistant oil displacement polymer.

[0019] In this disclosure and possible embodiments, the drying temperature is 50°C to 60°C, and the drying time is 10h to 15h.

[0020] This disclosure has the following beneficial effects:

[0021] The disclosed temperature- and salt-resistant polymer, firstly, introduces vinyl functional monomers with cyclic and large side-chain structures into the polymer molecular backbone to improve the hydrolysis resistance and shrinkage tendency of the synthesized polymer molecular backbone under extreme conditions, enabling the polymer to maintain the stability of the backbone structure under high temperature and high salinity conditions; secondly, by introducing N,N-diallyl-nalkylaniline monomers into the backbone, the main chain rigidity is further stabilized through the formation of cyclic structures during copolymerization, while the long-branched side groups provide stronger hydrodynamic volume, increasing the working viscosity of the polymer during oil displacement, further improving oil displacement efficiency, meeting the requirements for long-term polymer stability under harsh conditions, and also exhibiting good polymer solubility. Detailed Implementation

[0022] The present disclosure is described below based on embodiments; however, it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, certain specific details are described in detail. However, those skilled in the art will fully understand the present disclosure for the parts not described in detail.

[0023] Furthermore, unless the context explicitly requires it, the words "comprising," "including," and similar terms throughout the specification and claims should be interpreted as including rather than exclusive or exhaustive; that is, meaning "including but not limited to."

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the following embodiments are provided to further illustrate this invention in detail.

[0025] The preparation method of the heat-resistant and salt-resistant oil displacement polymers of the various embodiments of this disclosure is carried out according to the following steps:

[0026] (1) Acrylamide, sodium acrylate, vinyl monomer, N,N-diallyl-nalkylaniline monomer and cosolvent are purified and dissolved in an aqueous solution to obtain a reaction solution. The water used to prepare the monomer solution is deionized water that has been treated with cation exchange resin and anion exchange resin.

[0027] The percentages of each monomer in the total mass of the reaction raw materials are as follows: acrylamide 20%–25%; vinyl monomer 1.8%–2.3%; sodium acrylate 2.1%–2.5%; and N,N-diallyl-nalkylaniline monomer 0.5%–2.2%.

[0028] The co-solvent is one or a mixture of the following surfactants: sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and octylphenol polyoxyethylene ether. The amount of co-solvent used is 0.08% to 0.2% of the total mass of the reaction raw materials.

[0029] (2) Adjust the pH of the reaction solution to 8-12 using a pH adjuster;

[0030] (3) Transfer the prepared reaction solution to the reactor. Under nitrogen protection, control the temperature at 5-20°C. Add the initiator 15-20 min after nitrogen is introduced. The polymerization reaction lasts 8-12 hours to obtain the polymer colloid.

[0031] The initiator consists of an azo initiator and a redox initiator. The azo initiator is at least one of azobisisobutyramidine hydrochloride (V50), azobisisopropylimidazoline hydrochloride (VA044), and nitrile diisobutyronitrile (V60), and accounts for 0.005% to 0.015% of the total mass of the reactants. The oxidant in the redox initiator is one or more of hydrogen peroxide, cumene hydrogen peroxide, ammonium persulfate, and benzoyl peroxide. The reducing agent is one or more of sodium bisulfite, sodium sulfate, and sodium metabisulfite. The oxidant accounts for 0.01% to 0.03% of the total mass of the reactants, and the reducing agent accounts for 0.02% to 0.04% of the total mass of the reactants.

[0032] (4) The obtained polymer colloid is dried at 50℃~60℃ for 10h~15h, and the dried material is pulverized to obtain a heat-resistant and salt-resistant oil displacement polymer.

[0033] The raw materials used in the following specific embodiments of this disclosure are all purchased from commercially available products.

[0034] Example 1

[0035] 1. Raw material composition and content:

[0036] Acrylamide 240g, sodium acrylate 22g, vinylpyrrolidone 20g, N,N-diallyl-dodecylaniline 5g, sodium dodecyl sulfate 0.8g, ammonium persulfate (5% aqueous solution) 2mL, sodium bisulfite (5% aqueous solution) 4mL, azobisisopropylimidazoline hydrochloride (5% aqueous solution) 2mL, deionized water 704.2g, total 1000g.

[0037] 2. The preparation process of the temperature-resistant and salt-resistant polymer is as follows:

[0038] (1) Acrylamide, sodium acrylate, vinylpyrrolidone, N,N-diallyl-dodecylaniline and sodium dodecyl sulfate were purified and dissolved in deionized water to obtain a reaction solution, and the pH was adjusted to 11.5 with a pH adjuster.

[0039] (2) Transfer the reaction liquid to the reactor, and under nitrogen protection, control the temperature between 5 and 20°C. After 15 to 20 minutes of nitrogen purging, add ammonium persulfate, sodium bisulfite and azobisisopropylimidazoline hydrochloride. The polymerization reaction is carried out for 8 hours to obtain polymer colloid.

[0040] (3) The obtained colloid is dried at 50℃~60℃ for 12h, and the dried material is pulverized to obtain the heat-resistant and salt-resistant oil displacement polymer powder of Example 1.

[0041] 3. Polymer performance evaluation:

[0042] The salt resistance of polymers is characterized by viscosity. Under the same salinity conditions, the higher the viscosity of the polymer solution, the better its salt resistance.

[0043] The temperature resistance of a polymer is characterized by its viscosity retention rate after 30 days at high temperatures. At the same temperature, the higher the viscosity retention rate of the polymer solution, the better its temperature resistance.

[0044] The solubility of polymers is characterized by the water-insoluble matter index. Under the test conditions, if the water-insoluble matter of the polymer is ≤0.2%, it indicates that the polymer has good solubility.

[0045] In Example 1, the salt resistance test process of the polymer is as follows:

[0046] (1) Take the heat-resistant and salt-resistant polymer powder and the ordinary 25 million salt-resistant polymer (produced by Daqing Petrochemical Company) powder, and prepare 200g of polymer mother liquor with a concentration of 0.5%wt using simulated sewage (2%wt sodium chloride solution, 20000ppm).

[0047] (2) Weigh 40g of polymer mother liquor into a beaker, add simulated sewage to 200g, and mix with a magnetic stirrer for 10min to fully mix the 0.1% (1000ppm polymer concentration) polymer solution;

[0048] (3) The viscosity of the diluted polymer solution was measured using a Brookfield viscometer (manufactured by Brookfield) at 90°C and 6 rpm.

[0049] In Example 1, the polymer solubility test process is as follows:

[0050] (1) Weigh 2.5000g of the temperature-resistant and salt-resistant polymer sample as W.

[0051] (2) Weigh 497.50g of deionized water or secondary water into a 1000mL beaker, adjust the speed of the vertical stirrer to (400±20)r / min, so that the deionized water or secondary water forms a vortex, and slowly and evenly sprinkle the sample into the vortex wall within 30s. After stirring for 2h, let it stand for 30min to obtain a 0.5% sample solution.

[0052] (3) Insert the 25μm filter into the 47mm filter membrane holder and lock the holder.

[0053] (4) Add all of the 0.5% sample solution into the filter container, place the filter container on the device support, open the lower knob and the exhaust valve of the filter container, fill the clamp with liquid, then close the lower knob and the exhaust valve, and seal the top cover of the filter container.

[0054] (5) Start the device and set the air pressure to 0.2MPa.

[0055] (6) Open the knob at the bottom of the filter container, filter the sample solution with the weighed 25μm filter screen, and then rinse the filter screen with 500mL of deionized water or secondary water.

[0056] (7) Place the sieve back into the drying oven and dry it at 120°C for 2 hours. After cooling in the desiccator for 30 minutes, weigh it to an accuracy of 0.0001g and consider it as W5.

[0057] Water-insoluble matter is calculated using the following formula:

[0058]

[0059] In the formula: Nd—water-insoluble matter, %;

[0060] W4 — The mass of the sieve after drying, in grams (g);

[0061] W5 — The mass of the sieve and insoluble matter after drying, in grams (g);

[0062] W—mass of the sample, in grams (g).

[0063] The measurement results should be retained to three significant figures after the decimal point.

[0064] The performance evaluation results of the temperature-resistant and salt-resistant polymer and the ordinary 25 million polymer in Example 1 are shown in Table 1:

[0065] Table 1 Comparison of polymer performance evaluation results (polymer concentration 1000ppm)

[0066] polymer types Initial viscosity at 90℃ (mPas) Viscosity (mPas) after 30 days at 90℃ Viscosity retention % Water-insoluble matter % Example 1: Temperature-resistant and salt-resistant polymer 20.8 18.2 87.5 0.080 Ordinary 25 million polymer 11.2 7.4 66.0 0.124

[0067] As shown in the table above, under the same test conditions, the initial viscosity, viscosity at 90°C, viscosity after 30 days, and viscosity retention rate of Example 1 are all higher than those of ordinary polymers, while the water-insoluble matter content is lower than that of ordinary polymers.

[0068] Example 2

[0069] 1. Raw material composition and content:

[0070] Table 2 Monomer ratios of Example 2 and Example 1

[0071] monomer Example 2 Example 1 Acrylamide 24％ 24％ Sodium acrylate 2.2％ 2.2％ Vinylpyrrolidone 2％ 2％ N,N-Diallyl-dodecylaniline 1.0％ 0.5％

[0072] Acrylamide 240g, sodium acrylate 22g, vinylpyrrolidone 20g, N,N-diallyl-dodecylaniline 10g, sodium dodecylbenzenesulfonate 1.0g, potassium persulfate (5% aqueous solution) 4mL, sodium bisulfite (5% aqueous solution) 4mL, azobisisopropylimidazoline hydrochloride (5% aqueous solution) 2mL, deionized water 696.2g.

[0073] 2. The preparation method and performance evaluation method are the same as in Example 1.

[0074] The performance evaluation results of the temperature- and salt-resistant polymers of Examples 2 and 1 and the ordinary 25 million polymer are shown in Table 3:

[0075] Table 3 Comparison of polymer performance evaluation results (polymer concentration 1000ppm)

[0076] polymer types Initial viscosity at 90℃ (mPas) Viscosity (mPas) after 30 days at 90℃ Viscosity retention % Water-insoluble matter % Example 1: Temperature-resistant and salt-resistant polymer 20.8 18.2 87.5 0.080 Ordinary 25 million polymer 11.2 7.4 66.0 0.124 Example 2: Temperature-resistant and salt-resistant polymer 22.8 20.9 91.7 0.160

[0077] As shown in Table 3, under the same conditions, the initial viscosity and 30-day viscosity retention rate of Example 2 are both higher than those of the ordinary 25 million polymer. The amount of N,N-diallyl-dodecylaniline used in Example 2 is higher than that in Example 1, indicating that with the increase of N,N-diallyl-dodecylaniline content, the initial viscosity and viscosity retention rate of Example 2 are both higher than those of Example 1. Performance evaluation results show that the salt-resistant polymer of Example 2 has good salt resistance, and the salt resistance increases with the increase of the salt-resistant monomer content.

[0078] Example 3

[0079] 1. Raw material composition and content:

[0080] Table 4 Monomer ratios of Example 3 and Example 1

[0081] monomer Example 3 monomer Example 1 Acrylamide 24％ Acrylamide 24％ Sodium acrylate 2.2％ Sodium acrylate 2.2％ Sodium p-styrenesulfonate 2％ Vinylpyrrolidone 2％ N,N-Diallyl-dodecylaniline 1.0％ N,N-Diallyl-dodecylaniline 0.5％

[0082] Acrylamide 240g, sodium acrylate 22g, sodium p-styrene sulfonate 20g, N,N-diallyl-dodecylaniline 5g, sodium dodecyl sulfate 1.2g, potassium persulfate (5% aqueous solution) 3mL, sodium metabisulfite (5% aqueous solution) 5mL, azobisisopropylimidazoline hydrochloride (5% aqueous solution) 3mL, deionized water 702.8g.

[0083] 2. The preparation method and performance evaluation method are the same as in Example 1.

[0084] Table 5 shows the performance comparison results of the temperature- and salt-resistant polymers in Examples 3 and 1 with ordinary 25 million polymers:

[0085] Table 5 Comparison of polymer performance evaluation results (polymer concentration 1000ppm)

[0086]

[0087]

[0088] Example 4

[0089] 1. Raw material composition and content:

[0090] Table 6 Monomer ratios of Example 3 and Example 1

[0091] monomer Example 4 monomer Example 1 Acrylamide 24％ Acrylamide 24％ Sodium acrylate 2.2％ Sodium acrylate 2.2％ Sodium 2-acrylamido-2-methylpropanesulfonate 2％ Vinylpyrrolidone 2％ N,N-Diallyl-dodecylaniline 1.0％ N,N-Diallyl-dodecylaniline 0.5％

[0092] Acrylamide 240g, sodium acrylate 22g, sodium 2-acrylamido-2-methylpropanesulfonate 20g, N,N-diallyl-dodecylaniline 5g, sodium dodecyl sulfate 1.2g, potassium persulfate (5% aqueous solution) 4mL, sodium metabisulfite (5% aqueous solution) 5mL, azobisisobutyramidine hydrochloride (5% aqueous solution) 2.5mL, deionized water 702.3g.

[0093] 2. The preparation method and performance evaluation method are the same as in Example 1.

[0094] The performance evaluation results of the temperature- and salt-resistant polymers in Examples 4 and 1 compared with those of ordinary 25 million polymers are shown in Table 7:

[0095] Table 7 Comparison of polymer performance evaluation results (polymer concentration 1000ppm)

[0096] polymer type Initial viscosity at 90℃ (mPas) Viscosity (mPas) after 30 days at 90℃ Viscosity retention % Water-insoluble matter % Example 1: Temperature-resistant and salt-resistant polymer 20.8 18.2 87.5 0.080 Example 4: Temperature-resistant and salt-resistant polymer 20.4 18.1 88.7 0.048 Ordinary 25 million polymer 11.2 7.4 66.0 0.124

[0097] Example 5

[0098] 1. Raw material composition and content:

[0099] Acrylamide: 240g, Sodium acrylate: 22g, Sodium 2-acrylamido-2-methylpropanesulfonate: 20g, N,N-diallyl-tetradecylaniline: 5g, Sodium dodecyl sulfate: 2.0g, Potassium persulfate (5% aqueous solution): 4mL, Sodium metabisulfite (5% aqueous solution): 6mL, Azobisisobutyramidine hydrochloride (5% aqueous solution): 2.5mL, Deionized water: 698.5g.

[0100] 2. The preparation method is the same as in Example 1.

[0101] 3. Performance Evaluation:

[0102] (1) The temperature and salt resistance properties of the temperature-resistant and salt-resistant polymer of Example 5 and the ordinary 25 million polymer under oxygen exposure were tested. The specific test process is as follows:

[0103] ① Prepare 200g of polymer mother liquor with a concentration of 0.5%wt by using simulated sewage (10%wt sodium chloride solution, 100,000ppm) for both heat-resistant and salt-resistant polymer powder and ordinary 25 million salt-resistant polymer powder.

[0104] ② Weigh 80g of polymer mother liquor into a beaker, add simulated wastewater to 200g, and mix with a magnetic stirrer for 10min to fully mix the 0.2% (2000ppm polymer concentration) polymer solution;

[0105] ③ Using a Brookfield viscometer (manufactured by Brookfield Corporation), the initial viscosity was measured at 40°C and 6 rpm, and the thermostatic viscosity was measured at 90°C and 6 rpm.

[0106] Table 8. Test results of temperature and salt resistance under oxygen-exposed environment (polymer concentration 2000ppm)

[0107] polymer type Initial viscosity at 40℃ (mPas) Viscosity at 90℃ (mPas) Viscosity retention % Water-insoluble matter % Example 5: Temperature-resistant and salt-resistant polymer 35.2 31.8 90.3 0.160 Ordinary 25 million polymer 9.6 7.4 77.1 0.184

[0108] Oxygen can react with substances at high temperatures, decomposing and releasing active centers to form free radicals. These free radicals then cause polymers to undergo free radical chain reactions, breaking down long molecular chains into shorter ones. In the application of polymers for oil displacement, since polymers injected underground are generally in an oxygen-free state, the performance of polymers in this state is closer to that in actual use.

[0109] (2) The temperature and salt resistance performance tests of the temperature-resistant and salt-resistant polymer of Example 5 and the ordinary 25 million polymer under anaerobic conditions are as follows:

[0110] ① Take the temperature-resistant and salt-resistant polymer powder and the ordinary 25 million salt-resistant polymer and prepare 200g of polymer mother liquor with a concentration of 0.5%wt using simulated sewage (10%wt sodium chloride solution, 100,000ppm).

[0111] ② Weigh 100g of polymer mother liquor into a beaker, add simulated wastewater to 200g, and mix with a magnetic stirrer for 10min to fully mix the 0.2% (2000ppm polymer concentration) polymer solution;

[0112] ③ The obtained solution was deoxygenated under vacuum and then sealed in ampoules. It was placed in a 90℃ oven for 90 days, during which the viscosity value was measured every 30 days. Finally, the viscosity retention rate was measured after 120 days.

[0113] Table 9. Results of long-term temperature and salt resistance tests in an oxygen-free environment (polymer concentration 2000 ppm)

[0114]

[0115] The above results demonstrate that the polymer described in this patent application exhibits significantly improved initial viscosity and viscosity retention rate under high temperature and high mineralization conditions compared to ordinary salt-resistant polymers, demonstrating excellent performance under these conditions.

[0116] The embodiments described above are merely illustrative of implementation methods of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent disclosure. It should be noted that those skilled in the art can make various modifications, equivalent substitutions, and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent disclosure should be determined by the appended claims.

Claims

1. A heat-resistant and salt-resistant polymer for oil displacement, characterized in that, The molecular structural formula of the polymer is: Where: a, b, and c correspond to the molar percentage of structural units in the total units, a is 76%–79%, b is 7%–9%, ​​c is 8%–10%, and d is 100%–abc; n = 11, 13, 15; R1 is selected from the following groups:

2. The preparation method of the heat-resistant and salt-resistant polymer for oil displacement according to claim 1, characterized in that, include: Acrylamide, sodium acrylate, vinyl monomer, N,N-diallyl-nalkylaniline monomer and cosolvent are dissolved in deionized water to obtain a reaction solution, and the pH value of the reaction solution is adjusted to 8-12; under nitrogen protection, an initiator is added to the reaction solution, and the product of the polymerization reaction is the heat-resistant and salt-resistant oil displacement polymer.

3. The method for preparing the heat-resistant and salt-resistant polymer for oil displacement according to claim 2, characterized in that: The vinyl monomer is vinylpyrrolidone, sodium p-styrenesulfonate, or sodium 2-acrylamido-2-methylpropanesulfonate.

4. The method for preparing the heat-resistant and salt-resistant polymer for oil displacement according to claim 3, characterized in that: The co-solvent is one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and octylphenol polyoxyethylene ether, and the amount of the co-solvent is 0.08% to 0.2% of the total mass of the reaction raw materials.

5. The method for preparing the heat-resistant and salt-resistant polymer for oil displacement according to claim 4, characterized in that: The initiator is composed of azo initiators and redox initiators.

6. The method for preparing the heat-resistant and salt-resistant polymer for oil displacement according to claim 5, characterized in that: The azo initiator is at least one of azobisisobutyramidine hydrochloride, azobisisopropylimidazoline hydrochloride, and azobisisobutyronitrile, and the amount of the azo initiator is 0.005% to 0.015% of the total mass of the reaction raw materials; The oxidant in the redox initiator is one or more of hydrogen peroxide, cumene hydrogen peroxide, ammonium persulfate, and benzoyl peroxide; the reducing agent is one or more of sodium bisulfite, sodium sulfate, and sodium metabisulfite; the amount of the oxidant is 0.01% to 0.03% of the total mass of the reaction raw materials, and the amount of the reducing agent is 0.02% to 0.04% of the total mass of the reaction raw materials.

7. The method for preparing the heat-resistant and salt-resistant polymer for oil displacement according to any one of claims 2-6, characterized in that: The polymerization reaction time is 8 to 12 hours.

8. The method for preparing the heat-resistant and salt-resistant polymer for oil displacement according to claim 7, characterized in that: The polymerization reaction occurs in the reactor under nitrogen protection conditions. The temperature of the reactor is controlled at 5-20°C. The initiator is added 15-20 minutes after nitrogen is introduced.

9. The method for preparing the heat-resistant and salt-resistant polymer for oil displacement according to claim 8, characterized in that: The polymerization reaction is completed to obtain a polymer colloid; after the polymer colloid is dried, it is pulverized to obtain the heat-resistant and salt-resistant oil displacement polymer.

10. The method for preparing the heat-resistant and salt-resistant polymer for oil displacement according to claim 9, characterized in that: The drying process is carried out at a temperature of 50℃ to 60℃ for 10 hours to 15 hours.

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