Branched ultrahigh-salt and ultrahigh-temperature resistant polyacrylamide polymer as well as preparation method and application thereof

Abstract

The invention relates to a branched ultrahigh-salt and ultrahigh-temperature resistant polyacrylamide polymer as well as a preparation method and application thereof. The preparation method comprises the following steps: obtaining the polyacrylamide polymer with a branched structure by adopting a reducing agent octamethylpentaethylenehexamine; the branched polymer has a larger hydrodynamic volume and a denser intermolecular network structure, has better shear resistance, and can obtain a higher resistance factor and a higher residual resistance factor in a porous medium; and the problems of polymer molecule curl and obvious solution viscosity reduction caused by the electrostatic shielding effect can be weakened under the high-salt condition.

Description

Technical Field

[0001] The invention relates to a branched ultrahigh salt and ultrahigh temperature resistant polyacrylamide polymer and a preparation method and application thereof, belonging to the technical field of polymer synthesis. Background Art

[0002] Polymer flooding is an economical and effective method to improve crude oil recovery in tertiary oil recovery. Commonly used flooding polymers are mainly partially hydrolyzed polyacrylamide and its derivatives, which are highly hydrophilic, easy to form hydrogen bonds with water, easily soluble in water, and have a large hydrodynamic volume after hydration, which plays a role in viscosity enhancement. However, in brine with high salinity, divalent cations will neutralize the carboxyl anion effect of polymer molecules, causing the polymer molecules to curl up, and the acrylamide group will hydrolyze at high temperature, reducing the viscosity of the polymer solution. Therefore, it is necessary to add functional monomers to enhance its temperature and salt resistance and seek suitable initiators to increase the molecular weight of the polymer to achieve a higher viscosity enhancement effect. Existing polyacrylamide polymers are mostly linear structures. Under conditions of high salinity and high salinity, this type of polymer shows poor salt resistance, poor dispersion, and poor temperature resistance. It cannot meet the requirements of salinity above 32000mg / L and high temperature above 85℃ for Class III oil reservoirs, and is not suitable for promotion and application.

[0003] Chinese patent document CN118027942A discloses a novel salt-resistant polymer oil-displacing agent and a preparation method thereof. The novel salt-resistant polymer oil-displacing agent is obtained by adding quaternized polysulfone, epoxy nano-silica, coal tar resin, and 2-acrylamide-2-methylpropane sulfonic acid into a stirrer and stirring. During the stirring and mixing process, the epoxy nano-silica reacts with the hydroxyl groups in the quaternized polysulfone and the amino groups in the coal tar resin to generate a ring-opening reaction, and cross-linking is generated between the three, thereby enhancing the rigidity of the oil-displacing agent and providing good temperature and salt resistance. The quaternary ammonium salt polysulfone and the coal tar resin themselves have good salt resistance, but the salt resistance of the oil-displacing agent is still relatively low.

[0004] Chinese patent document CN117720683A discloses a method for preparing a heat-resistant and salt-resistant amphoteric polymer oil-displacing agent, which utilizes its steric effect and electrostatic action to improve the salt resistance and temperature resistance of the polymer, and introduces a new weak cationic monomer VI-L, so that the protonated tertiary amine on the imidazole ring of VI-L and the sulfonic acid group on AMPS interact electrostatically, thereby increasing the viscosity and salt resistance of the polymer. However, the heat and salt resistance still need to be improved.

[0005] In summary, there are almost no reports on ultra-high temperature and ultra-high salt resistant polymer oil displacement agents that can withstand temperatures above 95°C and have a resistance to complex salt mineralization of up to 58002 mg / L. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature, and a preparation method and application thereof.

[0007] The polymer prepared by the present invention has a branched structure, a larger fluid dynamics volume and a denser intermolecular network structure, a higher molecular weight and excellent viscosity-increasing properties, and has a significant viscosity-increasing effect in a high-temperature 95°C, 58002mg / L high-mineralization salt water (the solution viscosity at a polymer concentration of 2000mg / L still reaches 22.52mPa·s), exhibits excellent temperature resistance, salt resistance and shear recovery performance, has low cost, a simple synthesis method and is easy to use.

[0008] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical scheme:

[0009] A method for preparing a branched polyacrylamide polymer resistant to ultrahigh salt and ultrahigh temperature, comprising the following steps:

[0010] (1) mixing pentaethylenehexamine, formaldehyde and formic acid and heating them under reflux to obtain a reducing agent, octamethylpentaethylenehexamine;

[0011] (2) dissolving acrylamide, sulfonic acid monomer and functional monomer in deionized water, adding the reducing agent of step (1), adjusting the pH, cooling the mixed solution to below room temperature, transferring it to an insulated container, and introducing nitrogen;

[0012] (3) adding an oxidant to an insulated container and continuing to introduce nitrogen to react to obtain a transparent polymer gel;

[0013] (4) soaking and crushing the polymer gel obtained in step (3), filtering to obtain a white solid, and drying to obtain a branched polyacrylamide polymer resistant to ultrahigh salt and ultrahigh temperature.

[0014] Preferably, according to the present invention, in step (1), the volume ratio of pentaethylenehexamine, formaldehyde and formic acid is 1:(5-15):(10-30).

[0015] Preferably according to the present invention, in step (1), the volume ratio of pentaethylenehexamine, formaldehyde and formic acid is 1:10:20.

[0016] Preferably, in step (1), the heating reflux reaction is carried out at 85-95° C. for 20-30 h.

[0017] Preferably, according to the present invention, in step (1), after the reaction is completed, the pH is adjusted to 12 with saturated sodium hydroxide to obtain a mixed solution, the mixed solution is extracted with chloroform, the organic extract is collected and dried, and rotary evaporated to obtain the reducing agent octamethylpentaethylenehexamine.

[0018] Preferably according to the present invention, in step (2), the sulfonic acid monomer is 2-acrylamido-2-methylpropanesulfonic acid, and the functional monomer is acrylic acid or methacrylic acid. Preferably, the functional monomer is methacrylic acid, and is purified by rotary evaporation.

[0019] Preferably according to the present invention, in step (2), the oxidant is ammonium persulfate or potassium persulfate, and more preferably, the oxidant is potassium persulfate.

[0020] Preferably according to the present invention, in step (2), the mass of acrylamide monomer accounts for 30% to 70% of the total mass of monomers, preferably 40% to 60%, and more preferably 50%.

[0021] Preferably according to the present invention, in step (2), the functional monomer accounts for 0% to 5% of the total weight of the monomers.

[0022] More preferably, in step (2), the functional monomer accounts for 0% to 2% of the total weight of the monomers.

[0023] Preferably according to the present invention, in step (2), the total solid content of the monomers after being dissolved in water is 15 wt% to 30 wt%, preferably 20 wt%.

[0024] Preferably, according to the present invention, in step (2), adjusting the pH is to add sodium hydroxide solution to adjust the pH to 5 to 9, preferably 7 to 7.5.

[0025] Preferably according to the present invention, in step (3), the molar ratio of the reducing agent to the oxidizing agent is between 0.3:1 and 1.5:1, preferably between 0.6:1 and 1.2:1.

[0026] Preferably, according to the present invention, in step (3), the total amount of the oxidant and the reducing agent is 0.01 wt% to 0.05 wt%, preferably 0.02 wt% to 0.035 wt%, of the total mass of the monomers.

[0027] Preferably, according to the present invention, in step (3), the reaction is carried out at a temperature of 12 to 21° C. for 6 to 14 hours, and the time for introducing nitrogen is 0.5 to 1.0 hour.

[0028] According to a preferred embodiment of the present invention, in step (4), the obtained polymer gel is immersed in ethanol or acetone and crushed, and the white solid obtained by filtration is dried at 70-90° C. for 1-5 h.

[0029] A branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature is prepared by the method.

[0030] The branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature is used as an oil displacement agent.

[0031] According to the preferred embodiment of the present invention, the specific application method is as follows:

[0032] The branched polyacrylamide polymer that is resistant to ultra-high salt and ultra-high temperature is prepared into a 5000 mg / L polymer mother liquor, stirred at 500 r / min for 2 hours, and diluted into a 2000 mg / L polymer solution after standing for 24 hours, and then used for oil recovery under high temperature and high salt conditions.

[0033] The technical features and advantages of the present invention are as follows:

[0034] 1. The present invention changes the traditional linear structure of polyacrylamide polymers and adopts a reducing agent octamethylpentaethylenehexamine to obtain a branched structure polyacrylamide polymer; the branched polymer has a larger fluid dynamic volume and a denser intermolecular network structure, has better shear resistance, and can obtain a higher resistance factor and residual resistance factor in porous media, and can reduce the problem of polymer molecule curling and solution viscosity significantly reduced due to electrostatic shielding under high salt conditions.

[0035] 2. The branched ultra-high salt and ultra-high temperature resistant polyacrylamide polymer of the present invention introduces ionic groups with strong hydration properties into the molecular structure. The electrostatic repulsion and hydration of the ionic groups on the macromolecular chain will increase the hydrodynamic volume of the polymer molecules, making the solution have high viscosity. The viscosity-increasing effect is significant in 58002mg / L high-mineralization salt water (the solution viscosity is 39.65mPa·s when the polymer concentration is 2000mg / L)

[0036] 3. The ultra-high salt and ultra-high temperature resistant polyacrylamide-type oil recovery polymer of the present invention has extremely strong heat and salt resistance, and has a significant viscosity-increasing effect in 95°C high temperature, 58002mg / L high mineralization brine (the solution viscosity is still 22.52mPa·s when the polymer concentration is 2000mg / L).

[0037] 4. The ultra-high salt and ultra-high temperature resistant polyacrylamide-type oil displacement polymer of the present invention has extremely strong salt resistance and still has a high viscosity retention rate even in different types of ultra-high concentration salt solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the mass spectrum of octamethylpentaethylenehexamine obtained in Example 1.

[0039] Figure 2 This is the nuclear magnetic resonance spectrum of branched polyacrylamide polymers that are resistant to ultra-high salt and ultra-high temperature.

[0040] Figure 3 This is the infrared spectrum of branched polyacrylamide polymers that are resistant to ultra-high salt and ultra-high temperature.

[0041] Figure 4This is the shear resistance performance diagram of CX7#.

[0042] Figure 5 This is the characteristic viscosity diagram of CX7#. DETAILED DESCRIPTION

[0043] The present invention can be better understood according to the following examples. However, it is easy for those skilled in the art to understand that the contents described in the examples are only used to illustrate the present invention, and should not and will not limit the present invention described in detail in the claims.

[0044] Example 1

[0045] Preparation of octamethylpentaethylenehexamine:

[0046] In a three-necked flask, pentaethylenehexamine, formaldehyde and formic acid were added in a volume ratio of 1:10:20, and heated under reflux at 90°C for 24 hours. After the reaction, the pH was adjusted to 12 with saturated sodium hydroxide to obtain a mixed solution. The mixed solution was extracted with chloroform, and the organic extract was collected, dried and rotary evaporated to obtain the reducing agent octamethylpentaethylenehexamine C1#.

[0047] The mass spectrum of the reducing agent octamethylpentaethylenehexamine is shown in Figure 1 , indicating that the present invention successfully prepared the reducing agent octamethylpentaethylenehexamine.

[0048] Example 2

[0049] The preparation method of branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature comprises the following steps:

[0050] In the reactor, acrylamide and 2-acrylamido-2-methylpropanesulfonic acid were added in a mass ratio of 1:1, deionized water was added, the monomer solid content was controlled to 20wt%, and then C1# obtained in Example 1 was added as a reducing agent, and the solid matter was completely dissolved by stirring. Sodium hydroxide solution was added to the system to adjust the pH to 7.2, and the system was cooled to 12°C. After the temperature stabilized, the solution was transferred to an insulated container, and the oxidant potassium persulfate was added after nitrogen was passed for 0.5h. Among them, the molar ratio of the reducing agent to the oxidant was 0.6:1, and the total amount of the oxidant and the reducing agent was 0.02wt% of the total mass of the monomer. Stop passing nitrogen, continue the adiabatic reaction under this condition for 6h, place the obtained transparent rubber block in ethanol and soak and crush, filter the obtained white powder solid and dry it at 80°C for 3h to obtain the product CX1#, a polyacrylamide oil displacement polymer resistant to ultra-high salt and ultra-high temperature.

[0051] Example 3

[0052] The preparation method of branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature comprises the following steps:

[0053] In the reactor, acrylamide and 2-acrylamido-2-methylpropanesulfonic acid were added in a mass ratio of 1:1, deionized water was added, the monomer solid content was controlled to be 20wt%, and then C1# obtained in Example 1 was added as a reducing agent, and the solid matter was completely dissolved by stirring. Sodium hydroxide solution was added to the system to adjust the pH to 7.2, and the system was cooled to 15°C. After the temperature stabilized, the solution was transferred to an insulated container, and the oxidant potassium persulfate was added after nitrogen was passed for 0.5h. Among them, the molar ratio of the reducing agent to the oxidant was 0.8:1, and the total amount of the oxidant and the reducing agent was 0.025wt% of the total mass of the monomer. Stop passing nitrogen, continue the adiabatic reaction under this condition for 8h, place the obtained transparent glue block in ethanol and soak and crush, filter the obtained white powder solid and dry it at 80°C for 3h to obtain the product CX2#, a polyacrylamide oil displacement polymer resistant to ultra-high salt and ultra-high temperature.

[0054] Example 4

[0055] The preparation method of branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature comprises the following steps:

[0056] In the reactor, acrylamide and 2-acrylamido-2-methylpropanesulfonic acid were added in a mass ratio of 1:1, deionized water was added, the monomer solid content was controlled to 20wt%, and then C1# obtained in Example 1 was added as a reducing agent, and the solid matter was completely dissolved by stirring. Sodium hydroxide solution was added to the system to adjust the pH to 7.2, and the system was cooled to 18°C. After the temperature stabilized, the solution was transferred to an insulated container, and the oxidant potassium persulfate was added after nitrogen was passed for 0.5h. Among them, the molar ratio of the reducing agent to the oxidant was 1:1, and the total amount of the oxidant and the reducing agent was 0.03wt% of the total mass of the monomer. Stop passing nitrogen, continue the adiabatic reaction under this condition for 10h, place the obtained transparent rubber block in ethanol and soak and crush, filter the obtained white powder solid and dry it at 80°C for 3h to obtain the product CX3#, a polyacrylamide oil displacement polymer resistant to ultra-high salt and ultra-high temperature.

[0057] The NMR spectrum of polymer CX3# is shown in Figure 2 , infrared spectrum see Figure 3 .

[0058] Example 5

[0059] The preparation method of branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature comprises the following steps:

[0060] In the reactor, acrylamide and 2-acrylamido-2-methylpropanesulfonic acid were added in a mass ratio of 1:1, deionized water was added, the monomer solid content was controlled to 20wt%, and then C1# obtained in Example 1 was added as a reducing agent, and the solid matter was completely dissolved by stirring. Sodium hydroxide solution was added to the system to adjust the pH to 7.3, and the system was cooled to 21°C. After the temperature stabilized, the solution was transferred to an insulated container, and the oxidant potassium persulfate was added after nitrogen was passed for 0.5h. Among them, the molar ratio of the reducing agent to the oxidant was 1.2:1, and the total amount of the oxidant and the reducing agent was 0.035wt% of the total mass of the monomer. Stop passing nitrogen, continue the adiabatic reaction under this condition for 12h, place the obtained transparent rubber block in ethanol and soak and crush, filter the obtained white powder solid and dry it at 80°C for 3h to obtain the product CX4#, a polyacrylamide oil displacement polymer resistant to ultra-high salt and ultra-high temperature.

[0061] Example 6

[0062] The preparation method of branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature comprises the following steps:

[0063] In the reactor, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid were added in a mass ratio of 25:24:1, and deionized water was added to control the monomer solid content to 20wt%. Then, C1# obtained in Example 1 was added as a reducing agent, and the solid matter was completely dissolved by stirring. Sodium hydroxide solution was added to the system to adjust the pH to 7.3, and the system was cooled to 12°C. After the temperature stabilized, the solution was transferred to an insulated container, and the oxidant potassium persulfate was added after nitrogen was passed for 0.5h. Among them, the molar ratio of the reducing agent to the oxidant was 0.8:1, and the total amount of the oxidant and the reducing agent was 0.03wt% of the total mass of the monomer. Stop passing nitrogen, continue the adiabatic reaction under this condition for 14h, place the obtained transparent rubber block in ethanol and soak and crush, filter the obtained white powder solid and dry it at 80°C for 3h to obtain the product CX5#, a polyacrylamide oil displacement polymer resistant to ultra-high salt and ultra-high temperature.

[0064] Example 7

[0065] The preparation method of branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature comprises the following steps:

[0066] In the reactor, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid are added in a mass ratio of 25:24:1, and deionized water is added to control the monomer solid content to 20wt%. Then, C1# obtained in Example 1 is added as a reducing agent, and the solid matter is completely dissolved by stirring. Sodium hydroxide solution is added to the system to adjust the pH to 7.3, and the system is cooled to 15°C. After the temperature stabilizes, the solution is transferred to an insulated container, and the oxidant potassium persulfate is added after nitrogen is passed for 0.5h. Among them, the molar ratio of the reducing agent to the oxidant is 0.6:1, and the total amount of the oxidant and the reducing agent is 0.035wt% of the total mass of the monomer. Stop passing nitrogen, continue the adiabatic reaction under this condition for 7h, place the obtained transparent glue block in ethanol and soak and crush, filter the obtained white powder solid and dry it at 80°C for 3h to obtain the product CX6#, a polyacrylamide oil displacement polymer resistant to ultra-high salt and ultra-high temperature.

[0067] Example 8

[0068] The preparation method of branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature comprises the following steps:

[0069] In the reactor, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid were added in a mass ratio of 25:24:1, and deionized water was added to control the monomer solid content to 20wt%. Then, C1# obtained in Example 1 was added as a reducing agent, and the solid matter was completely dissolved by stirring. Sodium hydroxide solution was added to the system to adjust the pH to 7.3, and the system was cooled to 18°C. After the temperature stabilized, the solution was transferred to an insulated container, and the oxidant potassium persulfate was added after nitrogen was passed for 0.5h. Among them, the molar ratio of the reducing agent to the oxidant was 1.2:1, and the total amount of the oxidant and the reducing agent was 0.02wt% of the total mass of the monomer. Stop passing nitrogen, continue the adiabatic reaction under this condition for 9h, place the obtained transparent glue block in ethanol and soak and crush, filter the obtained white powder solid and dry it at 80°C for 3h to obtain the product CX7#, a polyacrylamide oil displacement polymer resistant to ultra-high salt and ultra-high temperature.

[0070] The NMR spectrum of polymer CX7# is shown in Figure 2 , infrared spectrum see Figure 3 .

[0071] Example 9

[0072] The preparation method of branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature comprises the following steps:

[0073] In the reactor, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid were added in a mass ratio of 25:24:1, and deionized water was added to control the monomer solid content to 20wt%. Then, C1# obtained in Example 1 was added as a reducing agent, and the solid matter was completely dissolved by stirring. Sodium hydroxide solution was added to the system to adjust the pH to 7.3, and the system was cooled to 21°C. After the temperature stabilized, the solution was transferred to an insulated container, and the oxidant potassium persulfate was added after nitrogen was passed for 0.5h. Among them, the molar ratio of the reducing agent to the oxidant was 1:1, and the total amount of the oxidant and the reducing agent was 0.025wt% of the total mass of the monomer. Stop passing nitrogen, continue the adiabatic reaction under this condition for 11h, place the obtained transparent glue block in ethanol and soak and crush, filter the obtained white powder solid and dry it at 80°C for 3h to obtain the product CX8#, a polyacrylamide oil displacement polymer resistant to ultra-high salt and ultra-high temperature.

[0074] Example 10

[0075] The preparation method of branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature comprises the following steps:

[0076] In the reactor, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid were added in a mass ratio of 25:23:2, and deionized water was added to control the monomer solid content to 20wt%. Then, C1# obtained in Example 1 was added as a reducing agent, and the solid matter was completely dissolved by stirring. Sodium hydroxide solution was added to the system to adjust the pH to 7.4, and the system was cooled to 12°C. After the temperature stabilized, the solution was transferred to an insulated container, and the oxidant potassium persulfate was added after nitrogen was passed for 0.5h. Among them, the molar ratio of the reducing agent to the oxidant was 1:1, and the total amount of the oxidant and the reducing agent was 0.035wt% of the total mass of the monomer. Stop passing nitrogen, continue the adiabatic reaction under this condition for 13h, place the obtained transparent rubber block in ethanol and soak and crush, filter the obtained white powder solid and dry it at 80°C for 3h to obtain the product CX9#, a polyacrylamide oil displacement polymer resistant to ultra-high salt and ultra-high temperature.

[0077] The NMR spectrum of polymer CX9# is shown in Figure 2 , infrared spectrum see Figure 3 .

[0078] Embodiment 11

[0079] The preparation method of branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature comprises the following steps:

[0080] In the reactor, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid are added in a mass ratio of 25:23:2, and deionized water is added to control the monomer solid content to 20wt%. Then, C1# obtained in Example 1 is added as a reducing agent, and the solid matter is completely dissolved by stirring. Sodium hydroxide solution is added to the system to adjust the pH to 7.4, and the system is cooled to 15°C. After the temperature stabilizes, the solution is transferred to an insulated container, and the oxidant potassium persulfate is added after nitrogen is passed for 0.5h. Among them, the molar ratio of the reducing agent to the oxidant is 1.2:1, and the total amount of the oxidant and the reducing agent is 0.03wt% of the total mass of the monomer. Stop passing nitrogen, continue the adiabatic reaction under this condition for 6h, place the obtained transparent glue block in ethanol and soak and crush, filter the obtained white powder solid and dry it at 80°C for 3h to obtain the product CX10#, a polyacrylamide oil displacement polymer resistant to ultra-high salt and ultra-high temperature.

[0081] Example 12

[0082] The preparation method of branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature comprises the following steps:

[0083] In the reactor, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid are added in a mass ratio of 25:23:2, and deionized water is added to control the monomer solid content to 20wt%. Then, C1# obtained in Example 1 is added as a reducing agent, and the solid matter is completely dissolved by stirring. Sodium hydroxide solution is added to the system to adjust the pH to 7.4, and the system is cooled to 18°C. After the temperature stabilizes, the solution is transferred to an insulated container, and the oxidant potassium persulfate is added after nitrogen is passed for 0.5h. Among them, the molar ratio of the reducing agent to the oxidant is 0.6:1, and the total amount of the oxidant and the reducing agent is 0.025wt% of the total mass of the monomer. Stop passing nitrogen, continue the adiabatic reaction under this condition for 8h, place the obtained transparent glue block in ethanol and soak and crush, filter the obtained white powder solid and dry it at 80°C for 3h to obtain the product CX11#, a polyacrylamide oil displacement polymer resistant to ultra-high salt and ultra-high temperature.

[0084] Example 13

[0085] The preparation method of branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature comprises the following steps:

[0086] In the reactor, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid are added in a mass ratio of 25:23:2, and deionized water is added to control the monomer solid content to 20wt%. Then, C1# obtained in Example 1 is added as a reducing agent, and the solid matter is completely dissolved by stirring. Sodium hydroxide solution is added to the system to adjust the pH to 7.4, and the system is cooled to 21°C. After the temperature stabilizes, the solution is transferred to an insulated container, and the oxidant potassium persulfate is added after nitrogen is passed for 0.5h. Among them, the molar ratio of the reducing agent to the oxidant is 0.8:1, and the total amount of the oxidant and the reducing agent is 0.02wt% of the total mass of the monomer. Stop passing nitrogen, continue the adiabatic reaction under this condition for 10h, place the obtained transparent glue block in ethanol and soak and crush, filter the obtained white powder solid and dry it at 80°C for 3h to obtain the product CX12#, a polyacrylamide oil displacement polymer resistant to ultra-high salt and ultra-high temperature.

[0087] Comparative Example 1

[0088] The same preparation method as described in Example 7, except that:

[0089] The C1 prepared in Example 1 was replaced with sodium bisulfite as a reducing agent to obtain a polyacrylamide-based oil recovery polymer DX# that is resistant to ultra-high salt and ultra-high temperature.

[0090] Experimental example: performance testing

[0091] 1. Polymer salt resistance test

[0092] Mineralized water with a mineralization degree of 58002 mg / L was prepared, and its composition was shown in Table 1. It was diluted in different proportions to obtain mineralized aqueous solutions with different mineralization degrees.

[0093] Table 1 Composition of mineralized water ingredients

[0094]

[0095] The above-mentioned mineralized water solutions with different mineralization degrees were used to prepare a CX7# solution with a concentration of 2000 mg / L, and its viscosity was tested; at the same time, the above-mentioned mineralized water with different mineralization degrees were used to prepare commercially available polyacrylamide (molecular weight of 20 million) solutions and DX# solutions with a concentration of 2000 mg / L, respectively, and their viscosities were tested and compared with CX7#. The results are shown in Table 2.

[0096] Table 2 Viscosity of CX7#, DX# and commercially available polyacrylamide in mineralized water at different concentrations

[0097]

[0098] As can be seen from Table 2, the viscosity of CX7# in mineralized water is much higher than that of commercially available linear polyacrylamide. Since the sulfonic acid group in the AMPS added in the embodiment is a strong polar group, it has strong hydrophilicity and strong electrostatic repulsion, which can increase the hydrodynamic volume of the polymer and improve salt resistance; at the same time, octamethylpentaethylenehexamine is used as a reducing agent, giving CX7# a branched structure, which can also increase the hydrodynamic volume of the polymer. The increase in hydrodynamic volume leads to an increase in solution viscosity, which makes CX7# have excellent salt resistance, while DX# uses sodium bisulfite as a reducing agent to obtain a linear polymer, and the viscosity of DX# is still less than that of CX7#.

[0099] 2. Temperature resistance test

[0100] CX7# and DX# solutions with a concentration of 2000 mg / L were prepared using 58002 mg / L mineral water, and their apparent viscosities were measured at different temperatures.

[0101] Table 3 Viscosity of CX7# and DX# at different temperatures

[0102]

[0103] It can be seen in the temperature change process that the viscosity of the polymer solution in the mineralized water decreases with the increase of temperature. This phenomenon can be explained from two aspects. On the one hand, with the increase of temperature, the irregular thermal motion of the polymer molecules in the solution intensifies, and the molecular conformation is easier to change, and the entanglement points between the polymer molecules are easier to be opened, resulting in a decrease in the force and entanglement density between the polymer molecules; on the other hand, the increase in temperature makes the polymer molecular chain more likely to curl up, the hydrodynamic radius of the polymer molecules becomes smaller, and the hydration effect is weakened, which further leads to an increase in the distance between molecules and a decrease in the entanglement density. The increase in the distance between molecules and the decrease in the entanglement density at the microscopic level are manifested as an increase in the apparent viscosity at the macroscopic level. Although the viscosity of the copolymer decreases during the heating process, the viscosity retention rate of the CX7# polymer at 95°C is still 56.80%, and the viscosity is 22.52mPa·s, which far exceeds the viscosity requirement for tertiary oil recovery (viscosity greater than 15mPa·s), which is enough to show that the polymer has good temperature resistance.

[0104] 3. Shear resistance test

[0105] Use 58002mg / L mineral water to prepare a CX7# solution with a concentration of 2000mg / L, and change the shear rate at 25℃ to measure its shear resistance.

[0106] The test results are as follows Figure 4 As shown, in the first shearing process, the shear rate is fixed at 7.34s -1, at this time, the solution viscosity is relatively stable. When entering the second shearing stage, the shear rate increases greatly, and the unwinding speed of the molecular chain also accelerates. Therefore, the viscosity of the solution decreases in this stage. After entering the third stage, it returns to 7.34s -1 At the shear rate of 1.5, the solution viscosity recovered rapidly and reached a new equilibrium state very quickly. After two high-speed shearing, the CX7# polymer was able to basically recover to its original viscosity, showing excellent shear recovery performance.

[0107] 4. Viscosity average molecular weight

[0108] According to the technical requirements of polyacrylamide for oil displacement in the enterprise standard Q / SH CG0159-2021 of China Petrochemical Corporation, the intrinsic viscosity of CX7# was measured using an Ubbelohde viscometer. The intrinsic viscosity of CX7# was obtained as shown in the following figure: Figure 5 As shown, its intrinsic viscosity is 2246mL / g, and the viscosity average molecular weight is calculated according to formula (1-1):

[0109]

[0110] The viscosity average molecular weight of the obtained polymer was 17.46 million.

[0111] The various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further explain various possible combinations.

Claims

1. A method for preparing a branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature, comprising the following steps: (1) mixing pentaethylenehexamine, formaldehyde and formic acid and heating them under reflux to obtain a reducing agent, octamethylpentaethylenehexamine; (2) dissolving acrylamide, sulfonic acid monomer and functional monomer in deionized water, adding the reducing agent of step (1), adjusting the pH, cooling the mixed solution to below room temperature, transferring it to an insulated container, and introducing nitrogen; (3) adding an oxidant to an insulated container and continuing to introduce nitrogen to react to obtain a transparent polymer gel; (4) soaking and crushing the polymer gel obtained in step (3), filtering to obtain a white solid, and drying to obtain a branched polyacrylamide polymer resistant to ultrahigh salt and ultrahigh temperature.

2. The preparation method according to claim 1, characterized in that: In step (1), the volume ratio of pentaethylenehexamine, formaldehyde and formic acid is 1:(5-15):(10-30).

3. The preparation method according to claim 1, characterized in that: In step (1), the heating reflux reaction is carried out at 85-95° C. for 20-30 hours. After the reaction is completed, the pH is adjusted to 12 with saturated sodium hydroxide to obtain a mixed solution. The mixed solution is extracted with chloroform, and the organic extract is collected and dried and rotary evaporated to obtain the reducing agent octamethylpentaethylenehexamine.

4. The preparation method according to claim 1, characterized in that: In step (2), the sulfonic acid monomer is 2-acrylamide-2-methylpropanesulfonic acid, the functional monomer is methacrylic acid, and the oxidant is ammonium persulfate or potassium persulfate.

5. The preparation method according to claim 1, characterized in that: In step (2), the mass of acrylamide monomer accounts for 30% to 70% of the total mass of monomers, the functional monomer accounts for 0% to 2% of the total mass of monomers, the total solid content of the monomers after being dissolved in water is 15wt% to 30wt%, and the pH is adjusted by adding sodium hydroxide solution to adjust the pH to 5 to 9, preferably 7 to 7.

5.

6. The preparation method according to claim 1, characterized in that: In step (3), the molar ratio of the reducing agent to the oxidizing agent is between 0.3:1 and 1.5:1, and the total amount of the oxidizing agent and the reducing agent is 0.01 wt% to 0.05 wt% of the total weight of the monomers, preferably 0.02 wt% to 0.035 wt%.

7. The preparation method according to claim 1, characterized in that: In step (3), the reaction is carried out at a temperature of 12 to 21° C. for 6 to 14 hours, and the time for introducing nitrogen is 0.5 to 1.0 hour.

8. The preparation method according to claim 1, characterized in that: In step (4), the obtained polymer gel is immersed in ethanol or acetone and crushed, and the white solid obtained by filtration is dried at 70-90° C. for 1-5 h.

9. A branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature, prepared by the method according to any one of claims 1 to 8.

10. Use of the branched ultra-high salt and ultra-high temperature resistant polyacrylamide polymer according to claim 9 as an oil displacement agent; The specific application methods are as follows: The branched polyacrylamide polymer that is resistant to ultra-high salt and ultra-high temperature is prepared into a 5000 mg / L polymer mother liquor, stirred at 500 r / min for 2 hours, and diluted into a 2000 mg / L polymer solution after standing for 24 hours, and then used for oil recovery under high temperature and high salt conditions.

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