A branched type superhigh salt resistant and superhigh temperature resistant polyacrylamide polymer, a preparation method and application thereof

Abstract

The application relates to a branched ultrahigh-salt-resistant and ultrahigh-temperature-resistant polyacrylamide polymer and a preparation method and application thereof. The branched polyacrylamide polymer is obtained by using a reducing agent octamethylpentavinylhexamine; the branched polymer has a larger hydrodynamic volume and a denser intermolecular network structure, has better shear resistance, can obtain higher resistance factors and residual resistance factors in a porous medium, and can weaken the problems of polymer molecule curling and significant reduction of solution viscosity caused by electrostatic shielding under high-salt conditions.

Description

Technical Field

[0001] This invention relates to a branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature, its preparation method and application, belonging to the field of polymer synthesis technology. Background Technology

[0002] Polymer flooding is an economical and effective method for improving crude oil recovery in tertiary oil recovery. Commonly used flooding polymers are mainly partially hydrolyzed polyacrylamide and its derivatives. These polymers are highly hydrophilic, readily forming hydrogen bonds with water, and are easily soluble in water. After hydration, they exhibit a large hydrodynamic volume, thus acting as a thickener. However, in highly saline solutions, divalent cations neutralize the carboxyl anions in the polymer molecules, causing molecular coiling. Furthermore, at high temperatures, acrylamide groups undergo hydrolysis, reducing the viscosity of the polymer solution. Therefore, it is necessary to add functional monomers to enhance its temperature and salt resistance and to seek suitable initiators to increase the polymer's molecular weight to achieve a higher thickening effect. Existing polyacrylamide polymers are mostly linear in structure. Under high salinity conditions, these polymers exhibit poor salt resistance, poor dispersion, and poor temperature resistance, failing to meet the requirements of salinity above 32000 mg / L and high temperatures above 85℃ in Class III reservoirs, thus hindering their widespread application.

[0003] Chinese patent document CN118027942A discloses a novel salt-resistant polymer oil displacement agent and its preparation method. The method involves adding quaternized polysulfone, epoxy nano-silica, coal tar pitch resin, and 2-acrylamide-2-methylpropanesulfonic acid to a stirrer and stirring to obtain the novel salt-resistant polymer oil displacement agent. During the mixing process, the epoxy nano-silica reacts with the hydroxyl groups in the quaternized polysulfone and the amino groups in the coal tar pitch resin through ring-opening, resulting in cross-linking and enhanced rigidity, thus exhibiting good temperature and salt resistance. While quaternized polysulfone and coal tar pitch resin themselves possess good salt resistance, the salt resistance of this oil displacement agent remains relatively low.

[0004] Chinese patent document CN117720683A discloses a method for preparing a temperature- and salt-resistant amphoteric polymer oil displacement agent. It utilizes the steric effect and electrostatic interaction to improve the salt and temperature resistance of the polymer. A novel weakly cationic monomer VI-L is introduced, which allows the protonated tertiary amine on the imidazole ring of VI-L to electrostatically interact with the sulfonic acid group on AMPS, increasing the polymer viscosity and salt resistance. However, the temperature and salt resistance still need to be improved.

[0005] In summary, there are almost no reports of polymer flooding agents that can withstand temperatures above 95°C and have a compound salt salinity of up to 58002 mg / L, and that are resistant to ultra-high temperature and ultra-high salt. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature conditions, its preparation method, and its applications.

[0007] The polymer prepared by this invention has a branched structure, with a larger hydrodynamic volume and a denser intermolecular network structure. It has a high molecular weight and excellent thickening properties. It exhibits significant thickening effect in brine with a high temperature of 95℃ and a high salinity of 58002 mg / L (the solution viscosity at a polymer concentration of 2000 mg / L still reaches 22.52 mPa·s). It also shows excellent temperature resistance, salt resistance and shear recovery performance. The polymer is low in cost, simple to synthesize and easy to use.

[0008] To achieve the aforementioned objective, the present invention employs the following technical solution:

[0009] A method for preparing a branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature includes the following steps:

[0010] (1) Pentylenehexamine, formaldehyde and formic acid are mixed and heated under reflux to prepare the reducing agent octamethylpentylenehexamine;

[0011] (2) Dissolve acrylamide, sulfonic acid monomer and functional monomer in deionized water, add the reducing agent from step (1), adjust the pH, cool the mixed solution to below room temperature, transfer it to an insulated container, and purge with nitrogen.

[0012] (3) Add an oxidant to an insulated container and continue to pass nitrogen gas through the reaction to obtain a transparent polymer gel;

[0013] (4) Soak and crush the polymer gel obtained in step (3), filter to obtain a white solid, dry to obtain a branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature.

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

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

[0016] According to a preferred embodiment of the present invention, in step (1), the heating and reflux reaction is carried out at 85-95°C for 20-30 hours.

[0017] According to a preferred embodiment of 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] According to a preferred embodiment of 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 it is purified by rotary evaporation.

[0019] According to a preferred embodiment of the present invention, in step (2), the oxidant is ammonium persulfate or potassium persulfate, and more preferably, the oxidant is potassium persulfate.

[0020] According to a preferred embodiment of 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] According to a preferred embodiment of the present invention, in step (2), the functional monomer accounts for 0% to 5% of the total mass of the monomer.

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

[0023] According to a preferred embodiment of the present invention, in step (2), the total solid content of the monomer after dissolving in water is 15wt% to 30wt%, preferably 20wt%.

[0024] According to a preferred embodiment of the present invention, in step (2), the pH is adjusted by adding sodium hydroxide solution to adjust the pH to 5-9, preferably 7-7.5.

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

[0026] According to a preferred embodiment of the present invention, in step (3), the total amount of oxidant and reducing agent is 0.01wt% to 0.05wt% of the total mass of the monomer, preferably 0.02wt% to 0.035wt%.

[0027] According to a preferred embodiment of the present invention, in step (3), the reaction is carried out at a temperature of 12-21°C for 6-14 hours, and the nitrogen gas is introduced for 0.5-1.0 hours.

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

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

[0030] The aforementioned branched polyacrylamide polymers, resistant to ultra-high salt and ultra-high temperature conditions, are used as oil displacement agents.

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

[0032] A branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature was prepared into a polymer mother liquor of 5000 mg / L, stirred at 500 r / min for 2 h, and then diluted to a polymer solution of 2000 mg / L after standing for 24 h. Oil displacement was then carried out under high temperature and high salt conditions.

[0033] Technical features and advantages of the present invention:

[0034] 1. This invention changes the traditional linear structure of polyacrylamide polymers by using octamethylpentaethylenehexamine as a reducing agent to obtain branched polyacrylamide polymers. Branched polymers have larger hydrodynamic volume and denser intermolecular network structure, better shear resistance, and can obtain higher resistance factor and residual resistance factor in porous media. Under high salt conditions, it can reduce the problems of polymer molecule curling and significant reduction in solution viscosity caused by electrostatic shielding.

[0035] 2. The branched polyacrylamide polymer of this invention introduces strongly hydratable ionic groups into its molecular structure. The electrostatic repulsion and hydration of these ionic groups on the macromolecular chain increase the hydrodynamic volume of the polymer molecules, resulting in a high-viscosity solution. The viscosity-enhancing effect is significant in high-mineralized brine (58002 mg / L), where the solution viscosity at a polymer concentration of 2000 mg / L is 39.65 mPa·s.

[0036] 3. The polyacrylamide-based oil displacement polymer of the present invention, which is resistant to ultra-high salt and ultra-high temperature, has extremely strong temperature and salt resistance. It has a significant thickening effect in brine with a high temperature of 95°C and a high salinity of 58002 mg / L (the solution viscosity at a polymer concentration of 2000 mg / L still reaches 22.52 mPa·s).

[0037] 4. The polyacrylamide-based oil displacement polymer of the present invention, which is resistant to ultra-high salt and ultra-high temperature, has extremely strong salt resistance and still has a high viscosity retention rate even in different types of ultra-high concentration salt solutions. Attached Figure Description

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

[0039] Figure 2 The NMR spectrum of a branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature.

[0040] Figure 3 Infrared spectra of branched polyacrylamide polymers resistant to ultra-high salt and ultra-high temperature.

[0041] Figure 4The diagram shows the shear resistance of CX7#.

[0042] Figure 5 The characteristic viscosity graph for CX7#. Detailed Implementation

[0043] The present invention can be better understood from the following embodiments. However, those skilled in the art will readily understand that the descriptions in the embodiments are for illustrative purposes only and should not, and will not, limit the invention as detailed in the claims.

[0044] Example 1

[0045] Preparation of octamethylpentaethylenehexamine:

[0046] Pentaethylenehexamine, formaldehyde, and formic acid were added to a three-necked flask in a volume ratio of 1:10:20. The mixture was heated under reflux at 90°C for 24 hours. After the reaction was completed, 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 prepared reducing agent octamethylpentaethylenehexamine is shown in the figure. Figure 1 This indicates that the reducing agent octamethylpentaethylenehexamine was successfully prepared by the present invention.

[0048] Example 2

[0049] The preparation method of branched polyacrylamide polymers resistant to ultra-high salt and ultra-high temperature is as follows:

[0050] Acrylamide and 2-acrylamido-2-methylpropanesulfonic acid were added to a reactor at a mass ratio of 1:1, followed by deionized water to control the monomer solid content at 20 wt%. Then, C1# prepared in Example 1 was added as a reducing agent, and the mixture was stirred until the solids were completely dissolved. Sodium hydroxide solution was added 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 nitrogen gas was purged for 0.5 h before adding potassium persulfate as an oxidant. The molar ratio of reducing agent to oxidant was 0.6:1, and the total amount of oxidant and reducing agent was 0.02 wt% of the total monomer mass. Nitrogen gas purging was stopped, and the reaction was continued under these conditions for 6 h under insulated conditions. The resulting transparent gel block was soaked in ethanol and pulverized. The resulting white powder was dried at 80°C for 3 h to obtain the product: CX1#, a polyacrylamide-based oil displacement polymer resistant to ultra-high salt and ultra-high temperature conditions.

[0051] Example 3

[0052] The preparation method of branched polyacrylamide polymers resistant to ultra-high salt and ultra-high temperature is as follows:

[0053] Acrylamide and 2-acrylamido-2-methylpropanesulfonic acid were added to a reactor at a mass ratio of 1:1, followed by deionized water to control the monomer solid content at 20 wt%. Then, C1# prepared in Example 1 was added as a reducing agent, and the mixture was stirred until the solids were completely dissolved. Sodium hydroxide solution was added 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 nitrogen gas was purged for 0.5 h before adding potassium persulfate as an oxidant. The molar ratio of reducing agent to oxidant was 0.8:1, and the total amount of oxidant and reducing agent was 0.025 wt% of the total monomer mass. Nitrogen gas purging was stopped, and the reaction was continued under these conditions for 8 h under insulated conditions. The resulting transparent gel block was soaked in ethanol and pulverized. The resulting white powder was dried at 80°C for 3 h to obtain the product, a polyacrylamide-based oil displacement polymer CX2# resistant to ultra-high salt and ultra-high temperature conditions.

[0054] Example 4

[0055] The preparation method of branched polyacrylamide polymers resistant to ultra-high salt and ultra-high temperature is as follows:

[0056] Acrylamide and 2-acrylamido-2-methylpropanesulfonic acid were added to a reactor at a mass ratio of 1:1, followed by deionized water to control the monomer solid content at 20 wt%. Then, C1# prepared in Example 1 was added as a reducing agent, and the mixture was stirred until the solids were completely dissolved. Sodium hydroxide solution was added 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 nitrogen gas was purged for 0.5 h before adding potassium persulfate as an oxidant. The molar ratio of reducing agent to oxidant was 1:1, and the total amount of oxidant and reducing agent was 0.03 wt% of the total monomer mass. Nitrogen gas purging was stopped, and the reaction was continued under these conditions for 10 h under insulated conditions. The resulting transparent gel block was soaked in ethanol and pulverized. The resulting white powder was dried at 80°C for 3 h to obtain the product, a polyacrylamide-based oil displacement polymer CX3# resistant to ultra-high salt and ultra-high temperature conditions.

[0057] The NMR spectrum of polymer CX3# is shown below. Figure 2 Infrared spectrum (see) Figure 3 .

[0058] Example 5

[0059] The preparation method of branched polyacrylamide polymers resistant to ultra-high salt and ultra-high temperature is as follows:

[0060] Acrylamide and 2-acrylamido-2-methylpropanesulfonic acid were added to a reactor at a mass ratio of 1:1, followed by deionized water to control the monomer solid content at 20 wt%. Then, C1# prepared in Example 1 was added as a reducing agent, and the mixture was stirred until the solids were completely dissolved. 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 nitrogen gas was purged for 0.5 h before adding potassium persulfate as an oxidant. The molar ratio of reducing agent to oxidant was 1.2:1, and the total amount of oxidant and reducing agent was 0.035 wt% of the total monomer mass. Nitrogen gas purging was stopped, and the reaction was continued under these conditions for 12 h under insulated conditions. The resulting transparent gel block was soaked in ethanol and pulverized. The resulting white powder was dried at 80°C for 3 h to obtain the product, a polyacrylamide-based oil displacement polymer CX4# resistant to ultra-high salt and ultra-high temperature conditions.

[0061] Example 6

[0062] The preparation method of branched polyacrylamide polymers resistant to ultra-high salt and ultra-high temperature is as follows:

[0063] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid were added to a reactor at a mass ratio of 25:24:1, along with deionized water to control the monomer solid content at 20 wt%. Then, C1# prepared in Example 1 was added as a reducing agent, and the mixture was stirred until the solids were completely dissolved. Sodium hydroxide solution was added 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 nitrogen gas was purged for 0.5 h before adding potassium persulfate as an oxidant. The molar ratio of reducing agent to oxidant was 0.8:1, and the total amount of oxidant and reducing agent was 0.03 wt% of the total monomer mass. Nitrogen gas purging was stopped, and the reaction was continued under these conditions for 14 h under insulated conditions. The resulting transparent gel block was soaked in ethanol and pulverized. The resulting white powder was dried at 80°C for 3 h to obtain the product: CX5#, a polyacrylamide-based oil displacement polymer resistant to ultra-high salt and ultra-high temperature conditions.

[0064] Example 7

[0065] The preparation method of branched polyacrylamide polymers resistant to ultra-high salt and ultra-high temperature is as follows:

[0066] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid were added to a reactor at a mass ratio of 25:24:1, along with deionized water, to control the monomer solid content at 20 wt%. Then, C1# prepared in Example 1 was added as a reducing agent, and the mixture was stirred until the solids were completely dissolved. Sodium hydroxide solution was added to adjust the pH to 7.3, and the system was cooled to 15°C. After the temperature stabilized, the solution was transferred to an insulated container, and nitrogen gas was purged for 0.5 h before adding potassium persulfate as an oxidant. The molar ratio of reducing agent to oxidant was 0.6:1, and the total amount of oxidant and reducing agent was 0.035 wt% of the total monomer mass. Nitrogen gas purging was stopped, and the reaction was continued under these conditions for 7 h under insulated conditions. The resulting transparent gel block was soaked in ethanol and pulverized. The resulting white powder was dried at 80°C for 3 h to obtain the product: CX6#, a polyacrylamide-based oil displacement polymer resistant to ultra-high salt and ultra-high temperature conditions.

[0067] Example 8

[0068] The preparation method of branched polyacrylamide polymers resistant to ultra-high salt and ultra-high temperature is as follows:

[0069] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid were added to a reactor at a mass ratio of 25:24:1, along with deionized water, to control the monomer solid content at 20 wt%. Then, C1# prepared in Example 1 was added as a reducing agent, and the mixture was stirred until the solids were completely dissolved. Sodium hydroxide solution was added 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 nitrogen gas was purged for 0.5 h before adding potassium persulfate as an oxidant. The molar ratio of reducing agent to oxidant was 1.2:1, and the total amount of oxidant and reducing agent was 0.02 wt% of the total monomer mass. Nitrogen gas purging was stopped, and the reaction was continued under these conditions for 9 h under insulated conditions. The resulting transparent gel block was soaked in ethanol and pulverized. The resulting white powder was dried at 80°C for 3 h to obtain the product: CX7#, a polyacrylamide-based oil displacement polymer resistant to ultra-high salt and ultra-high temperature conditions.

[0070] The NMR spectrum of polymer CX7# is shown below. Figure 2 Infrared spectrum (see) Figure 3 .

[0071] Example 9

[0072] The preparation method of branched polyacrylamide polymers resistant to ultra-high salt and ultra-high temperature is as follows:

[0073] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid were added to a reactor at a mass ratio of 25:24:1, along with deionized water, to control the monomer solid content at 20 wt%. C1# prepared in Example 1 was then added as a reducing agent, and the mixture was stirred until the solids were completely dissolved. Sodium hydroxide solution was added 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 nitrogen gas was purged for 0.5 h before adding potassium persulfate as an oxidant. The molar ratio of reducing agent to oxidant was 1:1, and the total amount of oxidant and reducing agent was 0.025 wt% of the total monomer mass. Nitrogen gas purging was stopped, and the reaction was continued under these conditions for 11 h under insulated conditions. The resulting transparent gel block was soaked in ethanol, pulverized, and filtered. The resulting white powdery solid was dried at 80°C for 3 h to obtain the product: CX8#, a polyacrylamide-based oil displacement polymer resistant to ultra-high salt and ultra-high temperature conditions.

[0074] Example 10

[0075] The preparation method of branched polyacrylamide polymers resistant to ultra-high salt and ultra-high temperature is as follows:

[0076] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid were added to a reactor at a mass ratio of 25:23:2, along with deionized water, to control the monomer solid content at 20 wt%. Then, C1# prepared in Example 1 was added as a reducing agent, and the mixture was stirred until the solids were completely dissolved. Sodium hydroxide solution was added 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 nitrogen gas was purged for 0.5 h before adding potassium persulfate as an oxidant. The molar ratio of reducing agent to oxidant was 1:1, and the total amount of oxidant and reducing agent was 0.035 wt% of the total monomer mass. Nitrogen gas purging was stopped, and the reaction was continued under these conditions for 13 h under insulated conditions. The resulting transparent gel block was soaked in ethanol, pulverized, and filtered. The resulting white powdery solid was dried at 80°C for 3 h to obtain the product: CX9#, a polyacrylamide-based oil displacement polymer resistant to ultra-high salt and ultra-high temperature conditions.

[0077] The NMR spectrum of polymer CX9# is shown below. Figure 2 Infrared spectrum (see) Figure 3 .

[0078] Example 11

[0079] The preparation method of branched polyacrylamide polymers resistant to ultra-high salt and ultra-high temperature is as follows:

[0080] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid were added to a reactor at a mass ratio of 25:23:2, along with deionized water, to control the monomer solid content at 20 wt%. Then, C1# prepared in Example 1 was added as a reducing agent, and the mixture was stirred until the solids were completely dissolved. Sodium hydroxide solution was added to adjust the pH to 7.4, and the system was cooled to 15°C. After the temperature stabilized, the solution was transferred to an insulated container, and nitrogen gas was purged for 0.5 h before adding potassium persulfate as an oxidant. The molar ratio of reducing agent to oxidant was 1.2:1, and the total amount of oxidant and reducing agent was 0.03 wt% of the total monomer mass. Nitrogen gas purging was stopped, and the reaction was continued under these conditions for 6 h under insulated conditions. The resulting transparent gel block was soaked in ethanol and pulverized. The resulting white powder was dried at 80°C for 3 h to obtain the product: CX10#, a polyacrylamide-based oil displacement polymer resistant to ultra-high salt and ultra-high temperature conditions.

[0081] Example 12

[0082] The preparation method of branched polyacrylamide polymers resistant to ultra-high salt and ultra-high temperature is as follows:

[0083] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid were added to a reactor at a mass ratio of 25:23:2, along with deionized water, to control the monomer solid content at 20 wt%. Then, C1# prepared in Example 1 was added as a reducing agent, and the mixture was stirred until the solids were completely dissolved. Sodium hydroxide solution was added to adjust the pH to 7.4, and the system was cooled to 18°C. After the temperature stabilized, the solution was transferred to an insulated container, and nitrogen gas was purged for 0.5 h before adding potassium persulfate as an oxidant. The molar ratio of reducing agent to oxidant was 0.6:1, and the total amount of oxidant and reducing agent was 0.025 wt% of the total monomer mass. Nitrogen gas purging was stopped, and the reaction was continued under these conditions for 8 h under insulated conditions. The resulting transparent gel block was soaked in ethanol and pulverized. The resulting white powder was dried at 80°C for 3 h to obtain the product: CX11#, a polyacrylamide-based oil displacement polymer resistant to ultra-high salt and ultra-high temperature conditions.

[0084] Example 13

[0085] The preparation method of branched polyacrylamide polymers resistant to ultra-high salt and ultra-high temperature is as follows:

[0086] Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and methacrylic acid were added to a reactor at a mass ratio of 25:23:2, along with deionized water, to control the monomer solid content at 20 wt%. Then, C1# prepared in Example 1 was added as a reducing agent, and the mixture was stirred until the solids were completely dissolved. Sodium hydroxide solution was added to adjust the pH to 7.4, and the system was cooled to 21°C. After the temperature stabilized, the solution was transferred to an insulated container, and nitrogen gas was purged for 0.5 h before adding potassium persulfate as an oxidant. The molar ratio of reducing agent to oxidant was 0.8:1, and the total amount of oxidant and reducing agent was 0.02 wt% of the total monomer mass. Nitrogen gas purging was stopped, and the reaction was continued under these conditions for 10 h under insulated conditions. The resulting transparent gel block was soaked in ethanol, pulverized, and filtered. The resulting white powdery solid was dried at 80°C for 3 h to obtain the product: CX12#, a polyacrylamide-based oil displacement polymer resistant to ultra-high salt and ultra-high temperature conditions.

[0087] Comparative Example 1

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

[0089] By replacing C1 obtained in Example 1 with sodium bisulfite as a reducing agent, a polyacrylamide-based oil displacement polymer DX# with ultra-high salt and ultra-high temperature resistance was obtained.

[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 is shown in Table 1. Mineralized water solutions with different mineralization degrees were obtained by diluting it at different ratios.

[0093] Table 1 Composition of mineralized water ingredients

[0094]

[0095] CX7# solutions with a concentration of 2000 mg / L were prepared using the mineralized aqueous solutions with different mineralization degrees mentioned above, and their viscosity was tested. At the same time, commercially available polyacrylamide (molecular weight of 20 million) solutions and DX# solutions with a concentration of 2000 mg / L were prepared using the mineralized aqueous solutions with different mineralization degrees mentioned above, and their viscosity was tested and compared with CX7#. The results are shown in Table 2.

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

[0097]

[0098] As shown in Table 2, the viscosity of CX7# in mineralized water is much higher than that of commercially available linear polyacrylamide. This is because the sulfonic acid groups in the AMPS added in the examples are strongly polar groups, exhibiting strong hydrophilicity and electrostatic repulsion, which increases the polymer's hydrodynamic volume and improves its salt resistance. Simultaneously, the use of octamethylpentaethylenehexamine as a reducing agent imparts a branched structure to CX7#, further increasing the polymer's hydrodynamic volume. This increase in hydrodynamic volume leads to increased solution viscosity, resulting in CX7#'s excellent salt resistance. In contrast, DX#, using sodium bisulfite as a reducing agent, is a linear polymer, and its viscosity remains lower than that of CX7#.

[0099] 2. Temperature resistance test

[0100] CX7# and DX# solutions with a concentration of 2000 mg / L were prepared using 5800 mg / L mineralized water, and their apparent viscosity was measured at different temperatures.

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

[0102]

[0103] During the temperature variation process, it was observed that the viscosity of the polymer solution in the mineralized water decreased with increasing temperature. This phenomenon can be explained in two ways. Firstly, as the temperature rises, the random thermal motion of polymer molecules in the solution intensifies, and the molecular conformation is more easily altered. The entanglement points between polymer molecules are more easily opened, resulting in a decrease in the intermolecular forces and entanglement density. Secondly, the increase in temperature makes the polymer molecular chains more prone to coiling, reducing the hydrodynamic radius of polymer molecules, weakening hydration, and further leading to an increase in intermolecular distance and a decrease in entanglement density. The increase in intermolecular distance and decrease in entanglement density at the microscopic level are macroscopically manifested as an increase in apparent viscosity. Although the viscosity of the copolymer decreased during the heating process, the viscosity retention rate of CX7# polymer at 95℃ was still 56.80%, with a viscosity of 22.52 mPa·s, far exceeding the viscosity requirement for tertiary oil recovery (viscosity greater than 15 mPa·s). This sufficiently demonstrates the good temperature resistance of the polymer.

[0104] 3. Shear resistance test

[0105] A CX7# solution with a concentration of 2000 mg / L was prepared using 5800 mg / L mineralized water, and its shear resistance was measured by changing the shear rate at 25℃.

[0106] Test results are as follows Figure 4 As shown, the shear rate is fixed at 7.34 s during the first shearing process. -1At this point, the solution viscosity is relatively stable. However, upon entering the second shear stage, the shear rate increases significantly, and the unwinding speed of the molecular chains also accelerates. Therefore, the solution viscosity decreases during this stage. Upon entering the third stage, it recovers to 7.34 s. -1 At the high shear rate, the solution viscosity rapidly recovers and quickly reaches a new equilibrium state. After two high-speed shear cycles, the CX7# polymer essentially recovers to its original viscosity, demonstrating excellent shear recovery performance.

[0107] 4. Viscosity-average molecular weight

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

[0109]

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

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

Claims

1. A method for preparing a branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature conditions, comprising the following steps: (1) Pentaethylenehexamine, formaldehyde, and formic acid are mixed and heated under reflux to prepare the reducing agent octamethylpentaethylenehexamine; the volume ratio of pentaethylenehexamine, formaldehyde, and formic acid is 1:(5-15):(10-30), the heating and reflux reaction is carried out at 85-95℃ for 20-30h, 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, dried and rotary evaporated to obtain the reducing agent octamethylpentaethylenehexamine; (2) Dissolve acrylamide, sulfonic acid monomer and functional monomer in deionized water, add the reducing agent from step (1), adjust the pH, cool the mixed solution to below room temperature, transfer it to an insulated container, and purge with nitrogen. (3) Add an oxidant to an insulated container and continue to pass nitrogen gas through the reaction to obtain a transparent polymer gel; (4) Soak and crush the polymer gel obtained in step (3), filter to obtain a white solid, dry to obtain a branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature.

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

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

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

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

6. The preparation method according to claim 1, characterized in that, In step (4), the obtained polymer gel is soaked and pulverized in ethanol or acetone, and the white solid obtained by filtration is dried at 70-90℃ for 1-5 hours.

7. A branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature, prepared by the method described in any one of claims 1-6.

8. The application of the branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature as described in claim 7, used as an oil displacement agent; the specific application method is as follows: A branched polyacrylamide polymer resistant to ultra-high salt and ultra-high temperature was prepared into a polymer mother liquor of 5000 mg / L, stirred at 500 r / min for 2 h, and then diluted to a polymer solution of 2000 mg / L after standing for 24 h. Oil displacement was then carried out under high temperature and high salt conditions.

Images