Polymeric surfactant for enhanced oil recovery

Abstract

The application belongs to the technical field of oil exploitation, and particularly relates to a polymer surfactant for enhanced oil recovery. The polymer surfactant is prepared by the following method: S1, adding acrylamide, 2-acrylamido-2-methylpropanesulfonic acid sodium, and methyl methacrylate into deionized water, and stirring uniformly to obtain a mixed monomer solution; S2, adding modified nano-silicon dioxide and modified gemini surfactant into the mixed monomer solution, stirring uniformly, adding an initiator, and performing polymerization to obtain the polymer surfactant. The polymer surfactant has good high-temperature resistance and salt resistance, can effectively reduce the oil-water interfacial tension, and is helpful to improve the oil recovery ratio. The polymer surfactant can effectively improve the oil recovery ratio when used for oil displacement.

Description

Technical Field

[0001] This invention belongs to the field of petroleum extraction technology, specifically relating to a polymer additive for enhancing oil recovery. Background Technology

[0002] Oil extraction is the industrial process of extracting oil and natural gas from underground reservoirs. It mainly includes primary oil recovery, secondary oil recovery, and tertiary oil recovery. Primary oil recovery relies on natural energy sources such as rock expansion, edge water drive, gravity, and natural gas expansion, but its recovery rate is limited. Secondary oil recovery increases reservoir pressure by injecting gas or water, replenishing elastic energy, preventing the establishment of a new pressure balance in the formation, and ensuring a continuous flow of fluid to the well. While this can improve the recovery rate, it requires additional energy input and equipment support. Tertiary oil recovery uses physical and chemical methods to change the viscosity of crude oil and its adsorption to rocks, which can further improve the recovery rate. This includes chemical flooding, gas flooding, thermal recovery, and microbial flooding. Chemical flooding involves adding chemical agents (polyacrylamide polymers, surfactants, and alkalis) to the injected water to improve the properties between the displacing fluid and the reservoir fluid, thereby increasing the crude oil recovery rate. It has the advantages of low energy consumption, low cost, and high oil displacement efficiency, and is widely used in oil extraction.

[0003] Chinese patent application CN202311833269.3 discloses a polymer-based binary composite oil displacement system and its application. The system comprises the following components by weight: 0.05-2 parts polymer-based surfactant, 0.01-2 parts biosurfactant, 0.001-1 part anti-adsorption agent, and 95.00-99.939 parts water. This system exhibits excellent anti-adsorption properties, ultra-low interfacial tension, and good emulsification properties, along with superior thermal stability. Furthermore, it can further improve oil recovery, outperforming conventional polymer-based binary oil displacement systems, with a maximum oil recovery rate of 38.97%. Chinese patent application CN202510138762.6 discloses... A surfactant for enhancing oil recovery in oilfields and its preparation method are disclosed. The surfactant is prepared from the following materials in parts: 10-500 parts petroleum sulfonate, 20-450 parts alkylbenzene sulfonate, 10-590 parts fatty alcohol, 1-50 parts ethylene oxide, 1-90 parts silica nanoparticles, 2-79 parts haloalkanes, 20-90 parts sodium hydroxide, 1-80 parts sodium carbonate, 5-50 parts xanthan gum, 1-78 parts carbon nanotubes, and 100-1000 parts water. This surfactant effectively reduces the interfacial tension between oil and water, making it easier for crude oil to peel off from the rock surface, thus improving oil displacement efficiency and achieving a total oil recovery of 55.3%. However, this surfactant has insufficient salt and high-temperature resistance. Therefore, it is necessary to develop a surfactant that is salt-resistant, high-temperature resistant, and can efficiently enhance oil recovery. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a polymer surface agent for improving oil recovery. The polymer surface agent provided by this invention has good high-temperature resistance and salt resistance. This polymer surface agent can effectively reduce the interfacial tension between oil and water, which helps to improve the oil recovery rate. Using the polymer surface agent provided by this invention for oil displacement can effectively improve the oil recovery rate.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows: A polymeric surface agent for enhancing oil recovery, said surface agent being prepared by the following method: S1. Add acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, and methyl methacrylate to deionized water and stir until homogeneous to obtain a mixed monomer solution. S2. Add modified nano-silica and modified Gemini surfactant to the mixed monomer solution, stir evenly, add initiator, and carry out polymerization reaction to obtain polymer surfactant.

[0006] Further, in step S1, the mass ratio of acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, methyl methacrylate, and deionized water is 40-50:10-15:5-10:100.

[0007] Furthermore, in step S2, the mass ratio of modified nano-silica, modified gemini surfactant, initiator, and mixed monomer solution is 4-5:8-10:1-2:100.

[0008] Furthermore, the initiator mentioned in step S2 is ammonium persulfate.

[0009] Furthermore, the polymerization reaction in step S2 is carried out at a temperature of 85-90°C for 3-4 hours.

[0010] Further, the modified nano-silica in step S2 is prepared by the following method: nano-silica is added to the reaction solvent and dispersed evenly, a modified Gemini surfactant is added, the pH value is adjusted to 5-6, and the mixture is placed at 40-50℃ and stirred for 5-6 hours to obtain modified nano-silica.

[0011] Furthermore, the mass ratio of the nano-silica to the modified Gemini surfactant is 1:0.2-0.3; the reaction solvent is a 50-60wt% aqueous ethanol solution.

[0012] Further, the modified gemini surfactant described in step S2 is prepared by the following method: (1) Add 4-dodecylaniline and N,N'-carbonyldiimidazole to acetonitrile, place at 25-30℃ and stir for 5-6h, then add 1,3-dichloro-2-propanol, heat to 70-80℃ and stir for 4-5h to obtain dichlorododecylaniline; (2) Add dichlorododecylaniline and dimethylaminoethyl methacrylate to toluene, stir evenly, place at 80-90℃ and stir for 7-8 hours, then place under ice bath conditions and slowly add chlorosulfonic acid. After the addition is complete, place at 20-25℃ and stir for 4-5 hours, then add saturated sodium hydroxide solution to neutralize to pH 8-9 to obtain the Gemini surfactant. (3) Add the gemini surfactant and triethylamine to anhydrous tetrahydrofuran, stir until homogeneous, protect with nitrogen, and slowly add 3-chloropropyltrimethoxysilane. After the addition is complete, place at 40-50℃ and stir for 5-6 hours to obtain the modified gemini surfactant.

[0013] Further, the molar ratio of 4-dodecylaniline, 1,3-dichloro-2-propanol, and N,N'-carbonyldiimidazole in step (1) is 1:1.1-1.2:1.2-1.3.

[0014] Further, in step (2), the molar ratio of dichlorododecylaniline, dimethylaminoethyl methacrylate, and chlorosulfonic acid is 1:2.1-2.2:1.1-1.2.

[0015] Further, in step (3), the molar ratio of the gemini surfactant, 3-chloropropyltrimethoxysilane, and triethylamine is 1:1.1-1.2:1.3-1.4.

[0016] The present invention has the following beneficial effects: The modified gemini surfactant provided by this invention is prepared by reacting 4-dodecylaniline as a raw material with N,N'-carbonyldiimidazole, 1,3-dichloro-2-propanol, dimethylaminoethyl methacrylate, chlorosulfonic acid, sodium hydroxide, and 3-chloropropyltrimethoxysilane in sequence. The modified gemini surfactant molecule contains hydrophobic long-chain alkyl groups, hydrophilic and high-temperature resistant, salt-resistant sodium phenylsulfonate groups, hydrophilic gemini quaternary ammonium salt groups, diethyl groups, and siloxane bonds. The diethyl groups and siloxane bonds enable it to participate in the polymerization reaction, improving the crosslinking density and stability of the polymer surfactant. The hydrophobic long-chain alkyl groups, hydrophilic and high-temperature resistant, salt-resistant sodium phenylsulfonate groups, and hydrophilic gemini quaternary ammonium salt groups also endow the polymer surfactant with good high-temperature resistance, salt resistance, and surface activity, enabling it to effectively reduce the oil-water interfacial tension. This invention, through the modification of gemini surfactant... The silica-oxygen bonds in the surfactant react with nano-silica, thereby grafting hydrophobic long-chain alkyl groups, hydrophilic and high-temperature resistant, salt-resistant sodium phenylsulfonate groups, hydrophilic gemini quaternary ammonium salt groups, and diethyl groups onto its surface to obtain modified nano-silica. The diethyl groups enable it to participate in the polymerization reaction, improving the bonding force between nano-silica and the surfactant, which helps to enhance the stability of the surfactant and allows nano-silica to be better adsorbed onto the rock surface, reducing the amount of crude oil adsorbed, thereby improving the crude oil recovery rate. It can also work with the hydrophobic long-chain alkyl groups, sodium phenylsulfonate groups, and gemini quaternary ammonium salt groups to reduce the oil-water interfacial tension. The modified gemini surfactant and modified nano-silica provided by this invention can work together to improve the high-temperature and salt resistance of the surfactant and reduce the oil-water interfacial tension, thereby greatly improving the crude oil recovery rate.

[0017] The polymer surfactant provided by this invention has good high temperature resistance and salt resistance. This polymer surfactant can effectively reduce the interfacial tension between oil and water, which helps to improve the oil recovery rate. Using the polymer surfactant provided by this invention for oil displacement can effectively improve the oil recovery rate. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The technical features designed in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] In the technical solution of this invention, all chemical reagents used are commercially available, including acrylamide (CAS No. 79-06-1), sodium 2-acrylamido-2-methylpropanesulfonate (CAS No. 15214-89-8), methyl methacrylate (CAS No. 80-62-6), ammonium persulfate (CAS No. 7727-54-0), 4-dodecylaniline (CAS No. 104-42-7), N,N'-carbonyldiimidazole (CAS No. 530-62-1), and 1,3-dichloro-2-propanol (CA). CAS No. S 96-23-1; CAS No. Dimethylaminoethyl methacrylate 2867-47-2; CAS No. Chlorosine 7790-94-5; CAS No. Sodium hydroxide 1310-73-2; CAS No. 3-chloropropyltrimethoxysilane 2530-87-2; CAS No. Triethylamine 121-44-8; CAS No. Acetonitrile 75-05-8; CAS No. Toluene 108-88-3; CAS No. Tetrahydrofuran 109-99-9; CAS No. Ethanol 64-17-5. Example 1

[0020] This embodiment provides a method for preparing a modified gemini surfactant:

[0021] (1) Add 13.0 g of 4-dodecylaniline and 9.7 g of N,N'-carbonyldiimidazole to 300 mL of acetonitrile, place at 25 °C and stir for 6 h, then add 7.1 g of 1,3-dichloro-2-propanol, heat to 80 °C and stir for 4 h. After the reaction is complete, remove the acetonitrile and obtain 18.2 g of dichlorododecylaniline by extraction and concentration; wherein the molar ratio of 4-dodecylaniline, 1,3-dichloro-2-propanol and N,N'-carbonyldiimidazole is 1:1.1:1.2; Dichlorododecylaniline: ESI (m / z): 417.4 [M+H] + , 1 H-NMR (600MHz, DMSO-d6, δppm): 9.88 (s, 1H), 7.53 (d, J=8.5Hz, 2H), 7.14 (d, J=8.5Hz, 2H), 5.29-5.32 ( m, 1H), 3.76-3.82 (m, 4H), 2.52-2.55 (m, 2H), 1.62-1.66 (m, 2H), 1.25-1.30 (m, 18H), 0.88-0.91 (m, 3H); (2) Add 18.2g of dichlorododecylaniline and 14.4g of dimethylaminoethyl methacrylate to 300mL of toluene, stir evenly, place at 90℃ and stir for 8h, then place in an ice bath and slowly add 5.6g of chlorosulfonic acid. After the addition is complete, place at 25℃ and stir for 5h, add saturated sodium hydroxide solution to neutralize to pH 9. After the reaction is complete, remove toluene, stir and remove impurities by diethyl ether, filter and dry to obtain 29.5g of Gemini surfactant; wherein the molar ratio of dichlorododecylaniline, dimethylaminoethyl methacrylate and chlorosulfonic acid is 1:2.1:1.1; Gemini surfactant: ESI (m / z): 833.9 [M+H] + , 1 H-NMR (600MHz, DMSO-d6, δppm): 9.86 (s, 1H), 8.01-8.05 (d, J=8.5Hz, 1H), 7.84 (s, 1H), 7.56-7.59 (d, J=8.5Hz, 1H), 6.42-6.47 (m, 4H), 5.30-5.34 (m , 1H), 4.58-4.62 (m, 4H), 3.52-3.60 (m, 8H), 3.30 (s, 12H), 2.51-2.55 (m, 2 H), 2.02 (s, 6H), 1.61-1.64 (m, 2H), 1.25-1.30 (m, 18H), 0.88-0.90 (m, 3H); (3) Add 29.5g of Gemini surfactant and 4.7g of triethylamine to 250mL of anhydrous tetrahydrofuran, stir evenly, under nitrogen protection, slowly add 7.7g of 3-chloropropyltrimethoxysilane, after the addition is complete, place at 50℃ and stir for 6h. After the reaction is complete, remove the anhydrous tetrahydrofuran, stir to remove impurities with diethyl ether, filter and dry to obtain 30.1g of modified Gemini surfactant; wherein the molar ratio of Gemini surfactant, 3-chloropropyltrimethoxysilane and triethylamine is 1:1.1:1.3; Modified Gemini surfactant: ESI (m / z): 996.2 [M+H] + , 1H-NMR (600MHz, DMSO-d6, δppm): 8.00-8.03 (d, J=8.5Hz, 1H), 7.85 (s, 1H), 7.56-7.5 8 (d, J=8.5Hz, 1H), 6.43-6.48 (m, 4H), 5.91-5.94 (m, 1H), 4.59-4.62 (m, 4H), 4.34-4 .38 (m, 2H), 3.55 (s, 9H) 3.46-3.50 (m, 8H), 3.31 (s, 12H), 2.52-2.55 (m, 2H), 2.01 (s , 6H), 1.63-1.67 (m, 4H), 1.26-1.30 (m, 18H), 0.89-0.92 (m, 3H), 0.56-0.59 (m, 2H). Example 2

[0022] This embodiment provides a polymeric surfactant for improving oil recovery, which is prepared by the following method: S1. Add acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, and methyl methacrylate to deionized water and stir until homogeneous to obtain a mixed monomer solution; wherein the mass ratio of acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, methyl methacrylate, and deionized water is 50:15:10:100.

[0023] S2. Add modified nano-silica and modified gemini surfactant to the mixed monomer solution, stir evenly, add initiator, and carry out polymerization reaction to obtain polymer surfactant; wherein the mass ratio of modified nano-silica, modified gemini surfactant, initiator, and mixed monomer solution is 5:10:2:100; the initiator is ammonium persulfate; the polymerization reaction temperature is 85℃ and the time is 4h.

[0024] Modified nano-silica was prepared by the following method: nano-silica was added to the reaction solvent and dispersed evenly. Modified Gemini surfactant was added, the pH was adjusted to 6, and the mixture was placed at 50°C and stirred for 6 hours. After the reaction was completed, the modified nano-silica was obtained by filtration and drying. The mass ratio of nano-silica to modified Gemini surfactant was 1:0.3. The reaction solvent was a 50wt% aqueous ethanol solution. Example 3

[0025] This embodiment provides a polymeric surfactant for improving oil recovery, which is prepared by the following method: S1. Add acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, and methyl methacrylate to deionized water and stir until homogeneous to obtain a mixed monomer solution; wherein the mass ratio of acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, methyl methacrylate, and deionized water is 45:10:5:100.

[0026] S2. Add modified nano-silica and modified gemini surfactant to the mixed monomer solution, stir evenly, add initiator, and carry out polymerization reaction to obtain polymer surfactant; wherein the mass ratio of modified nano-silica, modified gemini surfactant, initiator, and mixed monomer solution is 4.5:9:1.5:100; the initiator is ammonium persulfate; the polymerization reaction temperature is 87℃ and the time is 3.5h.

[0027] Modified nano-silica was prepared by the following method: nano-silica was added to the reaction solvent and dispersed evenly. Modified Gemini surfactant was added, the pH value was adjusted to 5.5, and the mixture was placed at 45°C and stirred for 5 hours. After the reaction was completed, the modified nano-silica was obtained by filtration and drying. The mass ratio of nano-silica to modified Gemini surfactant was 1:0.25. The reaction solvent was a 55wt% aqueous ethanol solution. Example 4

[0028] This embodiment provides a polymeric surfactant for improving oil recovery, which is prepared by the following method: S1. Add acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, and methyl methacrylate to deionized water and stir until homogeneous to obtain a mixed monomer solution; wherein the mass ratio of acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, methyl methacrylate, and deionized water is 40:12:8:100.

[0029] S2. Add modified nano-silica and modified Gemini surfactant to the mixed monomer solution, stir evenly, add initiator, and carry out polymerization reaction to obtain polymer surfactant; wherein the mass ratio of modified nano-silica, modified Gemini surfactant, initiator, and mixed monomer solution is 4:8:1:100; the initiator is ammonium persulfate; the polymerization reaction temperature is 90℃ and the time is 3h.

[0030] Modified nano-silica was prepared by the following method: nano-silica was added to the reaction solvent and dispersed evenly. Modified Gemini surfactant was added, the pH value was adjusted to 5, and the mixture was placed at 40°C and stirred for 5.5 h. After the reaction was completed, the modified nano-silica was obtained by filtration and drying. The mass ratio of nano-silica to modified Gemini surfactant was 1:0.2. The reaction solvent was a 60 wt% aqueous ethanol solution. Example 5

[0031] This embodiment provides a polymeric surfactant for improving oil recovery, which is prepared by the following method: S1. Add acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, and methyl methacrylate to deionized water and stir until homogeneous to obtain a mixed monomer solution; wherein the mass ratio of acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, methyl methacrylate, and deionized water is 45:15:6:100.

[0032] S2. Add modified nano-silica and modified gemini surfactant to the mixed monomer solution, stir evenly, add initiator, and carry out polymerization reaction to obtain polymer surfactant; wherein the mass ratio of modified nano-silica, modified gemini surfactant, initiator, and mixed monomer solution is 5:9:2:100; the initiator is ammonium persulfate; the polymerization reaction temperature is 90℃ and the time is 3.5h.

[0033] Modified nano-silica was prepared by the following method: nano-silica was added to the reaction solvent and dispersed evenly. Modified Gemini surfactant was added, the pH value was adjusted to 5.5, and the mixture was placed at 40°C and stirred for 6 hours. After the reaction was completed, the modified nano-silica was obtained by filtration and drying. The mass ratio of nano-silica to modified Gemini surfactant was 1:0.25. The reaction solvent was a 50wt% aqueous ethanol solution.

[0034] Comparative Example 1 This comparative example provides a polymeric surfactant for enhancing oil recovery, which is prepared by the following method: S1. Add acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, and methyl methacrylate to deionized water and stir until homogeneous to obtain a mixed monomer solution; wherein the mass ratio of acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, methyl methacrylate, and deionized water is 50:15:10:100.

[0035] S2. Add modified nano-silica to the mixed monomer solution, stir evenly, add initiator, and carry out polymerization reaction to obtain a polymer surface agent; wherein the mass ratio of modified nano-silica, initiator, and mixed monomer solution is 5:2:100; the initiator is ammonium persulfate; the polymerization reaction temperature is 85℃ and the time is 4h.

[0036] Modified nano-silica was prepared by the following method: nano-silica was added to the reaction solvent and dispersed evenly. Modified Gemini surfactant was added, the pH was adjusted to 6, and the mixture was placed at 50°C and stirred for 6 hours. After the reaction was completed, the modified nano-silica was obtained by filtration and drying. The mass ratio of nano-silica to modified Gemini surfactant was 1:0.3. The reaction solvent was a 50wt% aqueous ethanol solution.

[0037] Comparative Example 2 This comparative example provides a polymeric surfactant for enhancing oil recovery, which is prepared by the following method: S1. Add acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, and methyl methacrylate to deionized water and stir until homogeneous to obtain a mixed monomer solution; wherein the mass ratio of acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, methyl methacrylate, and deionized water is 50:15:10:100.

[0038] S2. Add nano-silica and modified gemini surfactant to the mixed monomer solution, stir evenly, add initiator, and carry out polymerization reaction to obtain polymerizer; wherein the mass ratio of nano-silica, modified gemini surfactant, initiator, and mixed monomer solution is 5:10:2:100; the initiator is ammonium persulfate; the polymerization reaction temperature is 85℃ and the time is 4h.

[0039] Comparative Example 3 This comparative example provides a polymeric surfactant for enhancing oil recovery, which is prepared by the following method: S1. Add acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, and methyl methacrylate to deionized water and stir until homogeneous to obtain a mixed monomer solution; wherein the mass ratio of acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, methyl methacrylate, and deionized water is 50:15:10:100.

[0040] S2. Add nano-silica to the mixed monomer solution, stir evenly, add initiator, and carry out polymerization reaction to obtain a polymer surface agent; wherein the mass ratio of nano-silica, initiator, and mixed monomer solution is 5:2:100; the initiator is ammonium persulfate; the polymerization reaction temperature is 85℃ and the time is 4h.

[0041] Test case The performance of the surfactants provided in Examples 2 to 5 and Comparative Examples 1 to 3 was tested, including tests on high temperature resistance and salt resistance: a high-mineralization salt solution containing 20 × 10⁻⁶ g / L was prepared. 4 The mineralization is 25 × 10 mg / L NaCl, 30000 mg / L CaCl2, and 20000 mg / L MgCl2. 4mg / L, a surfactant (concentration 0.15%) was added to high-salinity brine solutions, and the solutions were allowed to stand for 72 hours at different temperatures (80℃, 120℃) to observe their state. Interfacial tension testing was performed according to SY / T5370-2018 "Methods for Determination of Surface and Interfacial Tension," using a high-salinity brine solution containing a surfactant (concentration 0.15%) and crude oil as samples. Oil recovery testing: Natural core samples (8cm long, inner diameter...) were used. The core sample was 2.5 cm thick, with a porosity of 15.7% and a permeability of 38.8 mD. The temperature was 55℃. The core flooding method was used, simulating the formation water salinity as 30000 mg / L. Water was injected to drive oil until the produced fluid water cut was >99%, and the water recovery rate was calculated. Then, the polymer surfactant (concentration of 0.15%) provided in Examples 2 to 5 and Comparative Examples 1 to 3 was injected again, and water was injected again until the produced fluid water cut was >99%, and the increase in recovery rate was calculated. The results are shown in Table 1 below.

[0042] Table 1

[0043] As shown in Table 1, the polymer surfactants prepared in Examples 2 to 4 of this invention have good high-temperature resistance and salt resistance, effectively reducing oil-water interfacial tension and helping to improve oil recovery. Using the polymer surfactants provided by this invention for oil displacement can effectively improve crude oil recovery. Compared with Comparative Examples 1 to 3, the modified gemini surfactant in Example 2 of this invention contains hydrophobic long-chain alkyl groups, hydrophilic and high-temperature resistant, salt-resistant sodium phenylsulfonate groups, hydrophilic gemini quaternary ammonium salt groups, diethyl groups, and siloxane bonds. The diethyl groups and siloxane bonds enable them to participate in the polymerization reaction, improving the crosslinking density and stability of the polymer surfactant. The hydrophobic long-chain alkyl groups, hydrophilic and high-temperature resistant, salt-resistant sodium phenylsulfonate groups, and hydrophilic gemini quaternary ammonium salt groups also endow the polymer surfactant with good high-temperature resistance, salt resistance, and surface activity, enabling it to effectively... The modified nano-silica in Example 2 of this invention is grafted with hydrophobic long-chain alkyl groups, hydrophilic and high-temperature resistant, salt-resistant sodium phenylsulfonate groups, hydrophilic gemini quaternary ammonium salt groups, and diethyl groups. The diethyl groups enable the modified nano-silica to participate in the polymerization reaction, improving the bonding force between the nano-silica and the polymer surfactant, which helps to enhance the stability of the polymer surfactant and allows the nano-silica to be better adsorbed onto the rock surface, reducing the amount of crude oil adsorbed, thereby improving the crude oil recovery rate. It can also work with the hydrophobic long-chain alkyl groups, sodium phenylsulfonate groups, and gemini quaternary ammonium salt groups to reduce the oil-water interfacial tension. The modified gemini surfactant and modified nano-silica in Example 2 of this invention can work together to improve the high-temperature and salt resistance of the polymer surfactant, reduce the oil-water interfacial tension, and thus greatly improve the crude oil recovery rate.

[0044] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0045] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A polymer surfactant for enhancing oil recovery, characterized in that, The polymer surfactant is prepared by the following method: S1. Add acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, and methyl methacrylate to deionized water and stir until homogeneous to obtain a mixed monomer solution. S2. Add modified nano-silica and modified Gemini surfactant to the mixed monomer solution, stir evenly, add initiator, and carry out polymerization reaction to obtain polymer surfactant. The modified nano-silica was prepared by the following method: nano-silica was added to the reaction solvent and dispersed evenly. Modified Gemini surfactant was added, the pH value was adjusted to 5-6, and the mixture was placed at 40-50℃ and stirred for 5-6 hours to obtain modified nano-silica.

2. The oil recovery enhancer according to claim 1, characterized in that, The mass ratio of acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate, methyl methacrylate, and deionized water in step S1 is 40-50:10-15:5-10:

100.

3. A polymeric surfactant for enhancing oil recovery according to claim 1, characterized in that, In step S2, the mass ratio of modified nano-silica, modified gemini surfactant, initiator, and mixed monomer solution is 4-5:8-10:1-2:

100.

4. A polymeric surfactant for enhancing oil recovery according to claim 1, characterized in that, The modified gemini surfactant mentioned in step S2 is prepared by the following method: (1) Add 4-dodecylaniline and N,N'-carbonyldiimidazole to acetonitrile, place at 25-30℃ and stir for 5-6h, then add 1,3-dichloro-2-propanol, heat to 70-80℃ and stir for 4-5h to obtain dichlorododecylaniline; (2) Add dichlorododecylaniline and dimethylaminoethyl methacrylate to toluene, stir evenly, place at 80-90℃ and stir for 7-8 hours, then place under ice bath conditions and slowly add chlorosulfonic acid. After the addition is complete, place at 20-25℃ and stir for 4-5 hours, then add saturated sodium hydroxide solution to neutralize to pH 8-9 to obtain the Gemini surfactant. (3) Add the gemini surfactant and triethylamine to anhydrous tetrahydrofuran, stir until homogeneous, protect with nitrogen, and slowly add 3-chloropropyltrimethoxysilane. After the addition is complete, place at 40-50℃ and stir for 5-6 hours to obtain the modified gemini surfactant.

5. A polymeric surfactant for enhancing oil recovery according to claim 4, characterized in that, The molar ratio of 4-dodecylaniline, 1,3-dichloro-2-propanol and N,N'-carbonyldiimidazole in step (1) is 1:1.1-1.2:1.2-1.

3.

6. A polymeric surfactant for enhancing oil recovery according to claim 4, characterized in that, The molar ratio of dichlorododecylaniline, dimethylaminoethyl methacrylate, and chlorosulfonic acid in step (2) is 1:2.1-2.2:1.1-1.

2.

7. A polymeric surfactant for enhancing oil recovery according to claim 4, characterized in that, The molar ratio of the gemini surfactant, 3-chloropropyltrimethoxysilane, and triethylamine in step (3) is 1:1.1-1.2:1.3-1.

4.

8. A polymeric surfactant for enhancing oil recovery according to claim 1, characterized in that, The initiator mentioned in step S2 is ammonium persulfate.

9. A polymeric surfactant for enhancing oil recovery according to claim 1, characterized in that, The polymerization reaction in step S2 is carried out at a temperature of 85-90°C for 3-4 hours.

10. A polymeric surfactant for enhancing oil recovery according to claim 1, characterized in that, The mass ratio of the nano-silica to the modified Gemini surfactant is 1:0.2-0.3; the reaction solvent is a 50-60 wt% aqueous ethanol solution.

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