Temperature-resistant and salt-resistant polymer as well as preparation method and application thereof

Abstract

The invention relates to a temperature-resistant and salt-resistant polymer as well as a preparation method and application thereof, and belongs to the technical field of oil and gas exploitation. The method comprises the following steps: dissolving acrylamide, acrylic acid and a temperature-resistant monomer in a solvent to obtain a first solution; the preparation method comprises the following steps: reacting dimethylaminopropyl methacrylamide with brominated straight-chain alkane to obtain a salt-resistant monomer; dissolving the salt-resistant monomer in a solvent to obtain a second solution; mixing the first solution, the second solution and an auxiliary agent, and then reacting to obtain a temperature-resistant salt-resistant polymer; the salt-resistant monomer obtained through reaction of dimethylaminopropyl methacrylamide and brominated straight-chain alkane is a water-soluble amphiphilic hydrophobic monomer and can directly participate in polymerization reaction, an emulsifier does not need to be added, the aftertreatment process is reduced, and the purpose of solving the problem of high polymer preparation difficulty is achieved.

Description

Technical Field

[0001] This application relates to the field of oil and gas exploitation technology, and particularly to a temperature-resistant and salt-resistant polymer, its preparation method and application. Background Art

[0002] With the continuous development of oil fields, most oil fields have now entered the high water cut stage. In order to improve the recovery rate in the high water cut stage, the tertiary oil recovery technology is widely used, and among them, the chemical flooding agents mainly based on acrylamide materials are the most widely used. However, due to the limitations of the acrylamide structure itself, the temperature-resistant and salt-resistant properties of these products are insufficient, the high-temperature stability is poor, and they are prone to hydrolysis and degradation. Generally, they are applied to oil reservoirs below 90°C. At the same time, these products have poor salt tolerance, and using the produced water reinjected into the oil field for preparation will cause a significant reduction in the viscosity of the product solution, restricting the application of the product.

[0003] In recent years, technicians have improved the temperature-resistant and salt-resistant properties of polymers by introducing temperature-resistant and salt-resistant monomers into the molecular structure of partially hydrolyzed polyacrylamide. This structural modification changes the spatial configuration of the polyacrylamide molecular structure and its existence state in aqueous solution, enhancing the molecular structure rigidity and increasing the radius of gyration. Chinese Patent Application CN115368505A discloses a temperature-resistant and salt-resistant water-soluble hydrophobically associating polymer flooding agent and its preparation method. Its technical solution is copolymerized from three monomers: acrylamide, 3-allylamino-2-hydroxypropanesulfonic acid sodium, and cyclooctyl methacrylate. It shows good temperature-resistant and salt-resistant properties in brine with a salinity > 20000 mg / L. Chinese Patent Application CN115322290A discloses a temperature-sensitive calcium chloride-resistant nonionic hydrophobically associating polymer and its preparation method. The technical solution adopted is the copolymerization of acrylamide, octadecyl methacrylate, allyl polyethylene glycol, and N-vinylpyrrolidone. Under the synergistic action of hybrid rigid groups, polyethylene ether long-chain temperature-sensitive groups, and hydrophobic long-chain groups, the polymer has the ability to resist high-concentration calcium chloride and temperature sensitivity.

[0004] However, since most of the salt-resistant monomers are poorly soluble in water, an additional emulsifier needs to be added during synthesis to increase their water solubility, resulting in the need for a post-treatment step in the product preparation process and increasing the preparation difficulty. Summary of the Invention

[0005] This application provides a temperature-resistant and salt-resistant polymer, its preparation method and application to improve the problem of difficult polymer preparation.

[0006] In the first aspect, this application provides a preparation method of a temperature-resistant and salt-resistant polymer, and the method includes:

[0007] Dissolve acrylamide, acrylic acid, and temperature-resistant monomer in a solvent to obtain a first solution;

[0008] React dimethylaminopropyl methacrylamide with a brominated straight-chain alkane to obtain a salt-resistant monomer;

[0009] Dissolve the salt-resistant monomer in a solvent to obtain a second solution;

[0010] Mix the first solution, the second solution and an auxiliary agent, and then carry out a reaction to obtain a temperature-resistant and salt-resistant polymer.

[0011] As an alternative embodiment, the alkane of the brominated straight-chain alkane includes an alkane of C12 - C18.

[0012] As an alternative embodiment, the auxiliary agent includes a molecular weight regulator; and / or

[0013] The molecular weight regulator includes at least one of sodium formate, sodium acetate and isopropyl alcohol; and / or

[0014] The addition amount of the molecular weight regulator accounts for 0.002% - 0.008% of the total mass of acrylamide, acrylic acid, temperature-resistant monomer and salt-resistant monomer.

[0015] As an alternative embodiment, the auxiliary agent includes an initiator; and / or

[0016] The initiator includes a mixture of ammonium persulfate and sodium bisulfite, wherein the mass ratio of ammonium persulfate to sodium bisulfite is (0.5 - 1.5):(0.5 - 1.5); and / or

[0017] The addition amount of the initiator accounts for 0.06% - 0.2% of the total mass of acrylamide, acrylic acid, temperature-resistant monomer and salt-resistant monomer.

[0018] As an alternative embodiment, the temperature-resistant monomer includes at least one of 2-acrylamido-2-methylpropanesulfonic acid and N-vinylpyrrolidone; and / or

[0019] The mass ratio of acrylamide, acrylic acid, temperature-resistant monomer and salt-resistant monomer is: (70 - 75):(20 - 25):(4 - 6):(0.5 - 1).

[0020] As an alternative embodiment, the pH value of the first solution is 7 - 9.

[0021] As an alternative embodiment, the temperature of the reaction is 30 - 50°C; and / or

[0022] The time of the reaction is 2 - 8 h.

[0023] Second aspect, the present application provides a temperature and salt resistant polymer, which is prepared by using the preparation method of the temperature and salt resistant polymer described in the first aspect.

[0024] As an optional implementation manner, the structural formula of the polymer includes:

[0025] First structural formula:

[0026] Wherein, x / (y + z + m) = 70% - 75%, y / (y + z + m) = 20% - 25%, z / (y + z + m) = 4% - 6%, m / (y + z + m) = 0.5% - 1%, and n is 11 - 17;

[0027] Second structural formula:

[0028]

[0029] Wherein, x / (y + z + m) = 70% - 75%, y / (y + z + m) = 20% - 25%, z / (y + z + m) = 4% - 6%, m / (y + z + m) = 0.5% - 1%, and n is 11 - 17.

[0030] Second aspect, the present application provides an application of a temperature and salt resistant polymer. The polymer includes the polymer described in the second aspect, and the application includes: using the polymer for chemical flooding in oil and gas exploitation.

[0031] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0032] For the method provided by the embodiment of the present application, by using the salt resistant monomer obtained by reacting dimethylaminopropyl methacrylamide with brominated straight-chain alkane, which is a water-soluble amphiphilic hydrophobic monomer, it can directly participate in the polymerization reaction without adding an emulsifier, reducing the post-treatment process, and achieving the purpose of improving the difficult problem of polymer preparation. Description of the Drawings

[0033] The drawings here are incorporated into the specification and constitute a part of this specification, showing the embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0035] Figure 1 It is a flowchart of the method provided by the embodiment of the present application;

[0036] Figure 2 The initialization model of the polymer molecular monomer of the first structural formula constructed for the embodiments of the present application;

[0037] Figure 3 The initialization model of the polymer molecular monomer of the second structural formula constructed for the embodiments of the present application;

[0038] Figure 4 The polymer bulk structure model provided for the embodiments of the present application;

[0039] Figure 5 The polymer bulk structure model containing NaCl constructed for the embodiments of the present application (the aqueous phase is hidden);

[0040] Figure 6 The radial distribution function diagram of water molecules around the polymer under different salinity conditions provided for the embodiments of the present application;

[0041] Figure 7 The radius of gyration diagram of the polymer molecular chain at different temperatures provided for the embodiments of the present application. Detailed implementation manners

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the scope of protection of the present application.

[0043] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, and equipment used in the present application can be obtained through market purchase or can be prepared by existing methods.

[0044] The inventors found that: by introducing temperature-resistant and salt-resistant monomers into the molecular structure of partially hydrolyzed polyacrylamide, the temperature and salt resistance of the polymer can be improved. However, since most of the salt-resistant monomers are poorly soluble in water, an additional emulsifier needs to be added during synthesis to increase their water solubility, resulting in a post-treatment step in the product preparation process and increasing the preparation difficulty.

[0045] The inventors intend to provide a temperature-resistant and salt-resistant polymer, its preparation method and application to improve the problem of difficult polymer preparation.

[0046] Figure 1 The flowchart of the method provided for the embodiments of the present application. As Figure 1 shown, the embodiments of the present application provide a preparation method of a temperature-resistant and salt-resistant polymer, and the method includes:

[0047] S1. Dissolve acrylamide, acrylic acid and temperature-resistant monomer in a solvent to obtain a first solution;

[0048] In some embodiments, the temperature-resistant monomer includes at least one of 2-acrylamido-2-methylpropanesulfonic acid and N-vinylpyrrolidone.

[0049] In some embodiments, the pH value of the first solution is 7-9.

[0050] Specifically, in this embodiment, acrylamide, acrylic acid and temperature-resistant monomer are placed in a beaker, distilled water is added and stirred until the solution is transparent, and sodium hydroxide is added to adjust the pH value of the solution to neutral to weakly alkaline to obtain a first solution.

[0051] S2. React dimethylaminopropyl methacrylamide with brominated straight-chain alkane to obtain a salt-resistant monomer;

[0052] In some embodiments, the alkane of the brominated straight-chain alkane includes an alkane with 12-18 carbon atoms.

[0053] S3. Dissolve the salt-resistant monomer in a solvent to obtain a second solution;

[0054] Specifically, in this embodiment, the salt-resistant monomer is placed in a beaker, and distilled water is added and stirred evenly to prepare a second solution.

[0055] S4. Mix the first solution, the second solution and an auxiliary agent, and then react to obtain a temperature-resistant and salt-resistant polymer.

[0056] In some embodiments, the auxiliary agent includes a molecular weight regulator; the molecular weight regulator includes at least one of sodium formate, sodium acetate and isopropanol; the addition amount of the molecular weight regulator accounts for 0.002%-0.008% of the total mass of acrylamide, acrylic acid, temperature-resistant monomer and salt-resistant monomer.

[0057] In some embodiments, the auxiliary agent includes an initiator; the initiator includes a mixture of ammonium persulfate and sodium bisulfite, wherein the mass ratio of ammonium persulfate to sodium bisulfite is (0.5-1.5):(0.5-1.5); the addition amount of the initiator accounts for 0.06%-0.2% of the total mass of acrylamide, acrylic acid, temperature-resistant monomer and salt-resistant monomer.

[0058] In some embodiments, the mass ratio of acrylamide, acrylic acid, temperature-resistant monomer and salt-resistant monomer is: (70-75):(20-25):(4-6):(0.5-1).

[0059] In some embodiments, the temperature of the reaction is 30 to 50 °C; the time of the reaction is 2 to 8 h.

[0060] Specifically, in this embodiment, the second solution is poured into the first solution, a molecular weight regulator is added, and the mixture is stirred evenly; the obtained solution is transferred into a three-necked flask, an appropriate amount of distilled water is added, nitrogen is passed for 30 min, and then an initiator is added. The reaction is carried out at a constant temperature of 30 - 50 °C for 2 - 8 h to obtain a gel-like product; the gel-like product is crushed, immersed in absolute ethanol, soaked, washed, filtered to obtain a white solid substance, which is placed in an oven to be dried and pulverized to obtain a white solid powder, which is the obtained product, a temperature-resistant and salt-resistant polymer.

[0061] This method uses an anti-salt monomer obtained by reacting dimethylaminopropyl methacrylamide with a brominated straight-chain alkane. It is a water-soluble amphiphilic hydrophobic monomer, which can directly participate in the polymerization reaction without adding an emulsifier, reducing the post-treatment process and achieving the purpose of improving the difficult problem of polymer preparation.

[0062] Based on a general inventive concept, the embodiments of the present application further provide a temperature-resistant and salt-resistant polymer, which is prepared by using the preparation method of the temperature-resistant and salt-resistant polymer provided above.

[0063] This polymer is prepared based on the above method. The specific steps of this method can refer to the above embodiments. Since this polymer adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated here one by one.

[0064] When the temperature-resistant monomer added during preparation is 2-acrylamido-2-methylpropanesulfonic acid, the structural formula of the polymer is the first structural formula:

[0065]

[0066] Wherein, x / (y + z + m) = 70% - 75%, y / (y + z + m) = 20% - 25%, z / (y + z + m) = 4% - 6%, m / (y + z + m) = 0.5% - 1%, and n is 11 - 17.

[0067] When the temperature-resistant monomer added during preparation is N-vinylpyrrolidone, the structural formula of the polymer is the second structural formula:

[0068]

[0069] Wherein, x / (y + z + m) = 70% - 75%, y / (y + z + m) = 20% - 25%, z / (y + z + m) = 4% - 6%, m / (y + z + m) = 0.5% - 1%, and n is 11 - 17.

[0070] The polymer increases the rigidity of the molecular structure by introducing temperature-resistant monomers into the polyacrylamide copolymer chain, thereby enhancing its temperature resistance. By introducing anti-salt monomers with hydrophobic association effects, the polymer molecules aggregate in aqueous solutions due to their hydrophobic association, forming supramolecular structures and exhibiting excellent anti-salt properties. An aqueous solution with a polymer concentration of 0.2% is prepared with fresh water, and its viscosity is twice that of the comb-shaped polymer KY-2 when examined at 100 °C for 7 days. When prepared with reinjected water with a salinity of 40,000 mg / L (where Ca 2+ +Mg 2+ > 200 mg / L) and examined at 90 °C for 7 days, the viscosity of the 0.2% aqueous solution of this polymer is 1.5 - 2 times that of the polymer KY-2. When preparing a gel solution with the above reinjected water, the gel prepared with the polymer KY-2 breaks down after being examined at 100 °C for 15 days, while this polymer still has a viscosity above 500 mPa·s after being examined at 120 °C for 30 days.

[0071] Based on a general inventive concept, the embodiments of the present application further provide an application of a temperature-resistant and salt-resistant polymer. The polymer includes the polymer provided above, and the application includes: using the polymer in chemical flooding for oil and gas exploitation.

[0072] At the same time, the inventors found that when using indoor experimental methods such as viscometers or rheometers to measure the viscosity value of polymer solutions and evaluate the key physical and chemical properties such as the thickening ability, temperature resistance, and salt resistance of polymer molecules to guide their application scope in the field of tertiary oil recovery technology, this method is simple to operate, and the data is detailed, reliable, but it cannot reveal the microscopic structure and temperature-resistant and salt-resistant mechanism of the polymer. Chinese invention patent application CN108959844B discloses a method and system for evaluating the flow performance of polymer materials using molecular simulation methods. By using molecular simulation methods, not only can the flow performance of polymer materials be evaluated from a microscopic perspective, and the shear viscosity data of polymer materials can be calculated quickly, efficiently, and accurately, but also starting from the microscopic structure of the material (including molecular structure, molecular weight, degree of branching, functionalization, different formulation designs, etc.) and considering process conditions such as temperature and pressure, the key factors affecting the flow performance of polymer materials can be revealed. However, its accuracy and stability still need to be improved.

[0073] Therefore, the inventors intend to provide a new polymer evaluation method to improve the accuracy, rationality, and stability of the evaluation.

[0074] The technical solution adopted for polymer evaluation includes the following steps:

[0075] (1) Construct an initial model of polymer molecules

[0076] Construct the monomer of the polymer molecule to be tested (i.e., single-chain structure), and perform energy minimization on the constructed polymer molecule monomer. Based on the number of repeating units of the polymer monomer to be tested, construct the initial model of the polymer molecule on the basis of the energy-minimized polymer monomer structure;

[0077] (2) Perform quantum chemical geometry optimization on the polymer molecule structure

[0078] Perform energy minimization on the initial model of the polymer molecule in step (1) to obtain an optimized molecular structure data file;

[0079] (3) Judge the stable configuration of the polymer molecule

[0080] Extract the vibration frequency parameters in step (2), and judge whether the polymer molecule has reached the stable configuration of energy minimization according to whether there are negative values in the vibration frequency parameters;

[0081] (4) Build the bulk structure model of the polymer

[0082] Assign a force field and charges to the polymer molecule obtained in step (3), and build the bulk structure model of the polymer to be tested according to the structural parameters of the polymer to be tested, the component types and formulation ratios of additives such as inorganic salts, and perform the final force field and charge assignment on the bulk model;

[0083] (5) Perform molecular mechanics and molecular dynamics optimization on the bulk structure model of the polymer

[0084] Perform configuration optimization on the system finally obtained in step (4), and then perform heating and cooling annealing simulation calculations on the model to screen for the global optimal configuration;

[0085] (6) Perform molecular dynamics simulation on the model to obtain sufficient kinetic equilibrium

[0086] Perform molecular dynamics simulation of the NVT ensemble under specific temperature and pressure conditions on the optimal configuration obtained in step (5).

[0087] (7) Evaluate and analyze the kinetic trajectory data of the model

[0088] Perform correlation function analysis on the kinetic trajectory data to obtain polymer microstructure information, evaluate its performance indicators such as thickening viscosity, temperature resistance and salt resistance, and obtain the influence of factors such as temperature and inorganic salts on the polymer microstructure, and reveal the temperature and salt resistance mechanism of the polymer from the atomic and molecular perspective to further guide molecular design.

[0089] In step (1), both the monomer and polymer molecules are constructed using the Sketch tool in Materials Studio software; the energy minimization of the monomer is carried out using the Calculation tool in the DMol3 module and is processed using the quantum chemistry geometric optimization method.

[0090] In step (2), the energy minimization of the initial model of the polymer molecule needs to be completed using the Calculation tool in the DMol3 module.

[0091] In step (3), to determine the stable configuration of the polymer molecule, the vibrational frequency parameters in step (2) need to be extracted using Vibrational Analysis, and it is determined whether the polymer molecule has reached the stable configuration of energy minimization based on whether there are negative values in the vibrational frequency parameters; more specifically, if all the vibrational frequency parameters are positive, the molecular structure finally obtained in step (2) is the stable configuration of the polymer molecule; if there are negative values in the vibrational frequency parameters, the molecular structure corresponding to the negative value is finely adjusted along the vibration direction, and after repeating step (2), it is judged again according to the vibrational frequency parameters until all its vibrational frequency parameters are positive.

[0092] In step (4), the force field and charge are assigned to the polymer molecule and the polymer bulk phase model using the Discover module to select a suitable force field; more specifically, it is recommended to select COMPASS for the force field; the construction of the polymer bulk phase structure model needs to be completed using the Amorphous Cell module.

[0093] In step (5), the molecular mechanics optimization of the model needs to be completed using the Minimizer command in the Discover module and the Smart Minimizer method; the heating and annealing simulation calculation needs to be completed using the NPT ensemble with high frequency and multiple times, and in each annealing calculation, the molecular dynamics equilibrium of the NPT ensemble with a short time duration is carried out at the set temperature interval.

[0094] In step (6), the simulation temperature is regulated by the Andersen thermostat, and the pressure is regulated by the Berendsen barostat; the Velocity Verlet algorithm is used to solve the Newton's equation; the calculation method of the van der Waals interaction is selected as Atombased, the cutoff radius is 1.25 nm, and the part of the van der Waals interaction beyond the cutoff distance is corrected according to the mean density approximation method; the Coulomb interaction is calculated using the Ewald method, and its accuracy is controlled at 0.001 kcal / mol, the time step in the molecular dynamics simulation process is set to 1 fs, the dynamic trajectory of the system is recorded and saved every 1 ps, and the simulation time is at least 1 ns.

[0095] In step (7), the kinetic trajectory data is analyzed, including but not limited to data such as mean square displacement curve, radius of gyration, radial distribution function, stress autocorrelation function, etc., to obtain polymer property indexes such as water holding capacity, elastic modulus, shear resistance, solution viscosity, etc. and the influence of temperature and inorganic salts on the above microscopic properties.

[0096] This evaluation method innovatively introduces the quantum chemical geometry optimization method to obtain the stable configuration of polymer molecules, providing a more accurate and stable molecular configuration for subsequent molecular dynamics simulations and ensuring the accuracy and reliability of the simulation calculation results. In addition, by formulating detailed modeling steps for evaluating the temperature and salt resistance of polymers, key parameters such as solution viscosity, elastic modulus, shear resistance, and water holding capacity can be finally obtained, providing data support for systematically evaluating the temperature and salt resistance of polymers and revealing their microscopic action mechanisms.

[0097] The polymer evaluation method provided by this application has obvious advantages compared with the molecular mechanics optimization method involved in the prior art: molecular mechanics optimization is an optimization process based on the interaction of each atom of the molecule at the atomic level, while the quantum chemical geometry optimization method of the present invention is a process of optimizing the molecule from the electronic level using the Schrödinger equation. Therefore, the polymer molecular configuration optimized by the method of the present invention has the characteristics of being more precise, reasonable, and stable, thus further ensuring the accuracy and reliability of the simulation results of polymer properties. In addition, the present invention also provides polymer evaluation indexes and methods not limited to solution viscosity, which can systematically evaluate the microscopic structure and temperature and salt resistance of polymers from the atomic perspective, guiding molecular design while reducing the number of experiments and accelerating the research and development progress of new materials.

[0098] The following specific embodiments are used to further illustrate this application. It should be understood that these embodiments are only used to illustrate this application and not to limit the scope of this application. The experimental methods without specific conditions indicated in the following embodiments are usually determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0099] Example 1

[0100] A preparation method of a temperature and salt resistant polymer, the method comprising:

[0101] Step 1: Place 28 g of acrylamide, 10 g of acrylic acid, and 2 g of 2-acrylamido-2-methylpropanesulfonic acid in a beaker, add distilled water and stir to dissolve it to prepare a first solution;

[0102] Step 2: Add sodium hydroxide to Solution I to adjust the pH value to weakly alkaline;

[0103] Step 3: Place 0.4 g of the prepared salt-resistant monomer in a beaker, add distilled water and stir to dissolve it to prepare a second solution;

[0104] Step 4: Pour the second solution into the first solution, add 0.001 g of sodium formate, and stir evenly;

[0105] Step 5: Transfer the above solution to a three-necked flask, purge with nitrogen for 30 min, then add a mixture of 0.05 g of ammonium persulfate and sodium bisulfite with a mass ratio of 1:1. Heat to 50 °C and let stand for reaction. After 6 h, a transparent gel-like product is obtained.

[0106] Step 6: Cut the gel-like product into pieces, soak it in anhydrous ethanol, wash, filter to obtain a white solid substance, and dry and pulverize it in an oven to obtain the required temperature-resistant and salt-resistant polymer product.

[0107] Example 2

[0108] A method for preparing a temperature-resistant and salt-resistant polymer, the method comprising:

[0109] Step 1: Place 23 g of acrylamide, 6.2 g of acrylic acid, and 1.6 g of N-vinylpyrrolidone in a beaker, add 20 g of distilled water and stir to dissolve it to prepare a first solution;

[0110] Step 2: Add sodium hydroxide to Solution I to adjust the pH value to neutral;

[0111] Step 3: Place 0.2 g of the prepared salt-resistant monomer in a beaker, add 20 g of distilled water and stir to dissolve it to prepare a second solution;

[0112] Step 4: Pour the second solution into the first solution, add 0.001 g of sodium formate, and stir evenly;

[0113] Step 5: Transfer the above solution to a three-necked flask, add 53 g of distilled water, and purge with nitrogen for 30 min. Then add a mixture of 0.04 g of ammonium persulfate and sodium bisulfite with a mass ratio of 1:1, heat to 40 °C and let stand for reaction. After 4 h, a transparent gel-like product is obtained.

[0114] Step 6: Cut the gel-like product into pieces, soak it in anhydrous ethanol, wash, filter to obtain a white solid substance, and dry and pulverize it in an oven to obtain the required temperature-resistant and salt-resistant polymer product.

[0115] Comparative Example 1

[0116] KY-2 polymer purchased from the market.

[0117] The polymers provided in Example 1, Example 2 and Comparative Example 1 were formulated into a solution with a mass concentration of 0.2%, placed in an oven at different temperatures for 7 days, and the viscosity change of the solution was tested. The test results are shown in Table 1.

[0118] Table 1 Temperature and Salt Resistance Test of Polymer Solution (Salinity: 40,000 mg / L, where Ca 2+ +Mg 2+ > 200 mg / L brine preparation)

[0119]

[0120] 0.2% aqueous solutions of the three polymers in Example 1, Example 2 and Comparative Example 1 were respectively prepared with pure water, placed in an oven at 100 °C for 7 days, and the viscosities of their solutions were tested to be 88 mPa·s, 90 mPa·s, and 45 mPa·s respectively.

[0121] The polymers provided in Example 1, Example 2 and Comparative Example 1 were added with phenolic resin crosslinking agent to prepare a mobile gel. The formulation composition was 0.2% polymer, 0.3% phenolic resin crosslinking agent, and 0.2% crosslinking accelerator. It was placed in an oven at different temperatures for 30 days to test the gel viscosity change. The test results are shown in Table 2.

[0122] Table 2 Temperature and Salt Resistance Test of Polymer Prepared Mobile Gel (Salinity: 40,000 mg / L, where Ca 2+ +Mg 2+ > 200 mg / L brine preparation)

[0123] Test temperature, °C 70 80 90 100 110 120 Gel viscosity of the sample in Example 1, mPa·s 1695 1603 1543 1394 1244 540 Gel viscosity of the sample in Example 2, mPa·s 1895 1782 1604 1406 1300 501 Gel viscosity of the sample in Comparative Example 1, mPa·s 1002 894 512 Gel breaking Gel breaking Gel breaking

[0124] The polymers provided in Example 1 and Example 2 were evaluated. The evaluation process is as follows:

[0125] Step 1: Construct the initial model of the polymer molecule

[0126] Use the Sketch tool in Materials Studio software to complete the model construction of the polymer molecule monomer, such as Figure 2 and 3As shown below; Next, monomer energy minimization is carried out using the quantum chemical geometry optimization method. The Geometry Optimization method is adopted, with a fine precision selected and 300 calculation steps. The density functional theory (DFT) is used for the molecular structure optimization process. Specifically, the Calculation tool in the DMol3 module is used. During the optimization process, the rotation of the molecule is set to be unrestricted. The generalized gradient approximation (GGA) and the PBE density functional combination method (GGA-PBE) are used to calculate the electron exchange correlation energy. All electrons of the atoms are calculated using the all-electron method and expanded using the double numerical basis set plus polarization function (DNP); the number of monomer repeat units is calculated according to the polymer molecular weight and hydrolysis degree parameters, and based on the number of repeat units in the energy-minimized polymer monomer structure, the initial model of the polymer molecule is constructed;

[0127] Step 2: Quantum chemical geometry optimization of the polymer molecular structure

[0128] Perform energy minimization on the initial model of the polymer molecule in step (1). Refer to the parameter settings in step (1) and complete it using the Calculation tool in the DMol3 module to obtain the optimized molecular structure data file.

[0129] Step 3: Determine the stable configuration of the polymer molecule

[0130] Extract the vibration frequency parameters in step (2) using Vibrational Analysis, and determine whether the polymer molecule has reached the stable configuration of energy minimization based on whether the vibration frequency parameters are negative; if all the vibration frequency parameters are positive, the molecular structure finally obtained in step (2) is the stable configuration of the polymer molecule; if there are negative values among the vibration frequency parameters, fine-tune the molecular structure corresponding to the negative values along the vibration direction, repeat step (2) to continue the quantum chemical geometry optimization of the polymer molecular structure, and make a judgment based on the vibration frequency parameters obtained again until all of its vibration frequency parameters are positive, and obtain the stable configuration of the energy-minimized polymer molecule.

[0131] Step 4: Build the polymer bulk structure model

[0132] Use the Discover module to assign the force field and charge to the polymer molecule using the COMPASS force field; repeat step (1) to construct the water molecule model and use the Calculation tool in the DMol3 module to perform geometric structure optimization, and assign the force field and charge to the water molecule using the COMPASS force field; use the Amorphous Cell module to add 100,000 water molecules and 10 optimized polymer molecules to the bulk model, where the density is set to 1.0 g / cm 3; If the salt tolerance of the polymer is to be investigated, an appropriate amount of inorganic salt can be added to the above bulk phase model, such as adding 50 Na + and 50 Cl - . The initial bulk phase model of the polymer and the initial bulk phase model of the polymer containing salt are constructed, as shown in Figure 4 and Figure 5 respectively.

[0133] Step 5: Optimize the bulk phase structure model of the polymer by molecular mechanics and molecular dynamics

[0134] Use the Minimizer command in the Discover module to perform molecular mechanics optimization on the model obtained in Step 4. Select the Smart Minimizer method for optimization. For the heating and annealing simulation calculation, select the NPT ensemble with high frequency and multiple times, and perform molecular dynamics equilibration of the NPT ensemble for 200 - 500 ps at a set temperature interval of 20T in each annealing calculation.

[0135] Step 6: Perform molecular dynamics simulation on the model to obtain sufficient kinetic equilibrium

[0136] Use the Discover module to perform molecular dynamics simulation of the NVT ensemble under specific temperature and pressure conditions on the optimal configuration obtained in Step 5. The relevant parameters are set as follows: select Andersen for the thermostat, select Berendsen for the barostat for regulation, use the Velocity Verlet algorithm to solve the Newton's equation; select the Atombased method for calculating the van der Waals interaction, and set the cut-off radius to 1.25 nm; use the Ewald method to calculate the Coulomb interaction, and set its precision control to 0.001 kcal / mol. Set the time step during the molecular dynamics simulation to 1 fs, record and save the dynamic trajectory of the system every 1 ps, and the simulation time is 3 ns.

[0137] Step 7: Evaluate and analyze the kinetic trajectory data of the model

[0138] Use the Analysis tool in the Discover module to analyze the kinetic trajectory data of the last 2 ns obtained in Step 6 to obtain the radial distribution function of the polymer and water molecules ( Figure 6 shown), the radius of gyration of the polymer molecules ( Figure 7 shown), and the data of the elastic modulus and shear modulus of the polymer molecules (shown in Table 1).

[0139] Among them, the physical meaning of the radial distribution function (RDF) is: the probability of the appearance of particles at a distance r from the target particle. The structural information between particles and the orderliness of matter can both be investigated using the RDF. Therefore, the distribution of water molecules around the polymer can be studied through the radial distribution function.Figure 6 is the radial distribution function between the polymer and water molecules in different systems. The image shows that under different NaCl concentrations, the positions of the peaks of the radial distribution function of the polymer and water are the same. Therefore, the number of water molecules around the polymer can be characterized by the peak value, that is, the water-holding and water-retaining ability of the polymer. The higher the peak value, the more water molecules around the polymer, and the stronger the water-holding ability of the polymer; Figure 6 shows that a small amount of inorganic salt ions can increase the number of water molecules around the polymer, which is beneficial to the polymer's water-holding and water-retaining properties. However, excessive inorganic salt cations will weaken the water-holding and water-retaining ability of the polymer gel.

[0140] The radius of gyration of the polymer is an important parameter characterizing the molecular size of the polymer. Under the influence of external factors such as inorganic salts and temperature, the molecular size of the polymer in the solution will change, resulting in a change in the intrinsic viscosity η of the polymer solution (a characteristic parameter of the hydrodynamic volume formed by the molecular chain in the specified salt water). There is a certain relationship between the intrinsic viscosity and the radius of gyration: η = 63 / 2Φ(Rg)3 / M, where M is the molar mass of the polymer, Φ = 10πNA / 3, and NA is Avogadro's constant. Therefore, the change in the radius of gyration can reflect both the change in the system structure and the change in the intrinsic viscosity of the system. Figure 7 The results show that the radius of gyration of the polymer gradually decreases with the increase in temperature. This is mainly because at low temperatures, as the temperature increases, the thermal motion of the polymer molecules speeds up, and the electrostatic repulsion between the polymer chain segments weakens, causing the polymer chain to curl. The polymer's ability to attract water molecules increases, and the system viscosity increases. However, when the temperature is too high, the polymer chain curls excessively, resulting in the gradual compression of the configuration space, the loss of water molecules stored in the space, and the occurrence of high-temperature polymer dehydration phenomenon, which leads to a sharp drop in viscosity.

[0141] The elastic modulus and shear modulus are used to represent the rigidity of the material under different stress conditions, that is, the ability to resist elastic deformation. The elastic-plastic properties of the material, such as hardness, tensile strength, fracture strength, and tensile length, can be related to the elastic modulus. Hardness and tensile strength represent the ability to resist plastic deformation and are proportional to the shear modulus. The data in Table 3 show that compared with conventional polymerization (molecular weight ≥ 25 million, hydrolysis degree 23%-27%, model BHHP), the mechanical properties (elastic modulus, shear modulus) of the polymer molecules of the first structural formula synthesized in the present invention are better.

[0142] Table 3 Comparison of mechanical property indexes of different polymer molecules

[0143] Index BHHP (≥25 million) Molecular formula 1 Elastic modulus E, GPa 6.52 8.02 Shear modulus G, GPa 5.43 6.71

[0144] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the description of the said range has specifically disclosed all possible sub-ranges and the individual values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and the individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, which applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0145] In the present application, unless otherwise stated, the orientation terms such as "upper" and "lower" specifically refer to the drawing directions in the drawings. Additionally, in the description of the present application specification, the terms "comprising", "including", etc. mean "including but not limited to". In this document, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the association relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B may be singular or plural. In this document, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one of the following (items)", or similar expressions refer to any combination of these items, including any combination of single item (s) or plural items (s). For example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0146] The above description is only the specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a temperature-resistant and salt-resistant polymer, characterized in that: The method comprises: Dissolving acrylamide, acrylic acid and a temperature-resistant monomer in a solvent to obtain a first solution; The salt-resistant monomer is obtained by reacting dimethylaminopropyl methacrylamide with brominated straight-chain alkane; dissolving the salt-resistant monomer in a solvent to obtain a second solution; The first solution, the second solution and the auxiliary agent are mixed and then reacted to obtain a temperature-resistant and salt-resistant polymer.

2. The method for preparing a heat-resistant and salt-resistant polymer according to claim 1, characterized in that: The alkanes of the brominated straight-chain alkanes include alkanes of C12 to C18.

3. The method for preparing the heat-resistant and salt-resistant polymer according to claim 1, characterized in that: The auxiliary agent includes a molecular weight regulator; and / or The molecular weight regulator comprises at least one of sodium formate, sodium acetate and isopropanol; and / or The added amount of the molecular weight regulator accounts for 0.002% to 0.008% of the total mass of the acrylamide, acrylic acid, heat-resistant monomer and salt-resistant monomer.

4. The method for preparing a heat-resistant and salt-resistant polymer according to claim 1, characterized in that: The auxiliary agent includes an initiator; and / or The initiator comprises a mixture of ammonium persulfate and sodium bisulfite, wherein the mass ratio of the ammonium persulfate to the sodium bisulfite is (0.5-1.5): (0.5-1.5); and / or The added amount of the initiator accounts for 0.06%-0.2% of the total mass of the acrylamide, acrylic acid, temperature-resistant monomer and salt-resistant monomer.

5. The method for preparing a heat-resistant and salt-resistant polymer according to claim 1, characterized in that: The temperature-resistant monomer comprises: at least one of 2-acrylamido-2-methylpropanesulfonic acid and N-vinyl pyrrolidone; and / or The mass ratio of acrylamide, acrylic acid, heat-resistant monomer and salt-resistant monomer is: (70-75): (20-25): (4-6): (0.5-1).

6. The method for preparing a heat-resistant and salt-resistant polymer according to claim 1, characterized in that: The pH value of the first solution is 7-9.

7. The method for preparing a heat-resistant and salt-resistant polymer according to claim 1, characterized in that: The reaction temperature is 30-50°C; and / or The reaction time is 2 to 8 hours.

8. A temperature-resistant and salt-resistant polymer, characterized in that: The polymer is prepared by the preparation method of the temperature-resistant and salt-resistant polymer according to any one of claims 1 to 7.

9. The heat-resistant and salt-resistant polymer according to claim 8, characterized in that: The structural formula of the polymer includes: The first structural formula: Among them, x / (y+z+m)=70%~75%, y / (y+z+m)=20%~25%, z / (y+z+m)=4%~6%, m / (y+z+m)=0.5%~1%, n is 11~17; Second structural formula: Among them, x / (y+z+m)=70% to 75%, y / (y+z+m)=20% to 25%, z / (y+z+m)=4% to 6%, m / (y+z+m)=0.5% to 1%, and n is 11 to 17.

10. An application of a temperature-resistant and salt-resistant polymer, characterized in that: The polymer comprises the polymer described in any one of claims 8 to 9, and the application comprises: using the polymer for chemical flooding in oil and gas production.

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