An oil recovery agent for oil production and a method for preparing the same

Abstract

The present application relates to oil displacement agent technical field, specifically to a kind of oil exploitation class oil displacement agent and preparation method thereof, comprising the following steps: modified active agent is added to deionized water, stirring is dispersed completely, and active agent aqueous solution is obtained, nano-silica modified solvent is added to active agent aqueous solution, and oil displacement agent is obtained by stirring.The present application is grafted by nano-silica surface block structure, and hydrophobic monomer is oriented distribution at molecular chain end, can form high strength, high toughness interface film at oil-water interface quickly, significantly reduce interface interaction energy;While relying on the steric hindrance effect of block structure, reasonable flow control is formed in pore, inhibits oil displacement agent channeling, expands swept volume, modified nanoparticle and block polymer can enter small pore, rely on interface film strong force peeling and adsorbing oil;While reasonable particle size and space structure improve flow state in pore, improve the adaptability to low-permeability, complex pore reservoir.

Description

Technical Field

[0001] This invention relates to the field of oil displacement agents, and in particular to an oil displacement agent for petroleum extraction and its preparation method. Background Technology

[0002] As most of my country's major oilfields enter the later stages of development characterized by high water cut and high recovery rates, waterflooding recovery rates are low, with a large amount of residual oil remaining on the surface of rock pores and in low-permeability channels. Improving recovery rates has become a core requirement for ensuring stable crude oil production. Chemical flooding, as a key technology for tertiary oil recovery, mainly relies on polymers, surfactants, and composite systems to improve the mobility ratio and reduce the oil-water interfacial tension, thereby achieving efficient utilization of residual oil.

[0003] Current mainstream oil displacement agents often suffer from the problem of simultaneously achieving good interfacial activity and mobility control. While single surfactant systems can reduce interfacial tension, they are prone to channeling along high-permeability layers, resulting in limited affected volume. Polymer systems, although capable of regulating mobility, struggle to efficiently strip adsorbed crude oil. Furthermore, traditional oil displacement agents exhibit poor salt tolerance, easily experiencing molecular chain coiling, sudden viscosity drops, and surfactant deactivation in high-calcium and magnesium ion formations, making them unsuitable for high-salinity oil reservoir environments. Therefore, to address the problems described above, this invention proposes an oil displacement agent for petroleum extraction and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide an oil displacement agent for petroleum extraction and its preparation method, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing an oil displacement agent for petroleum extraction, comprising the following steps:

[0006] S1. Add the modified surfactant to deionized water and stir until completely dispersed to obtain an aqueous surfactant solution.

[0007] S2. Add the nano-silica modified solvent to the activator aqueous solution, stir for 30-60 min, adjust the pH to 7-8, and let it stand for 2-4 h to obtain the oil displacement agent.

[0008] The nano-silica modified solvent is prepared through the following steps:

[0009] S21. Add silica initiator, acrylamide, and catalytic system to a mixed solvent, and deoxygenate by liquid nitrogen freezing, vacuuming, and thawing cycles 2-3 times. Polymerize at 60-65℃ for 6-12 hours to obtain modified silica intermediate.

[0010] S22. In an oxygen-free atmosphere, add octyl acrylate hydrophobic monomer to the modified silica intermediate and polymerize at 60-65℃ for 6-10 hours. Add methanol to terminate the reaction and precipitate. Wash and dry the precipitate to obtain the silica graft.

[0011] S23. Disperse the silica graft in anhydrous ethanol, add the nanosheet aqueous dispersion, and stir for 2-2.5 h to obtain the nano-silica modified solvent.

[0012] The nanosheet aqueous dispersion is prepared through the following steps:

[0013] Trifluorotoluene, 4-cyano-4-(thiobenzoyl)valerate, sodium bicarbonate, and deionized water are mixed and heated to 30-35°C under nitrogen protection. A fluorinated monomer is then added dropwise. UV initiation was performed at a wavelength of 365 nm and a power of 400 W for 30-40 minutes, followed by the addition of zwitterionic monomers. Continue UV-initiated polymerization for 30-40 minutes, then centrifuge after the reaction ends and dialyze for 72-96 hours to obtain an aqueous dispersion of nanosheets.

[0014] As a preferred embodiment of the present invention, the silica initiator in step S21 is prepared through the following steps:

[0015] S211. Prepare a silica dispersion by mixing nano-silica with ethanol, add 3-aminopropyltriethoxysilane, reflux at 78-82℃ for 5-6 hours, wash with ethanol, centrifuge 2-3 times, and vacuum dry to obtain aminated silica.

[0016] S212. Disperse aminated silica in anhydrous ethanol, add 2-bromoisobutyryl bromide as an initiator precursor, add triethylamine dropwise at 0-2℃, and react at room temperature for 10-12 h.

[0017] S213. After the reaction is complete, the precipitate is collected by centrifugation. The precipitate is washed with ethanol and tetrahydrofuran alternately and then centrifuged again. The washed precipitate is then dried under vacuum to obtain the silica initiator.

[0018] As a preferred embodiment of the present invention, the modified surfactant in step S1 is prepared through the following steps:

[0019] S11. Add nanocellulose to anhydrous ethanol, adjust the pH to 3-4 with dilute hydrochloric acid, stir for 10-15 min to obtain a dispersion, add KH-570 to the dispersion, react at 60-65℃ for 3-4 h, after the reaction is complete, centrifuge to collect the precipitate, wash the precipitate 2-3 times with anhydrous ethanol to obtain modified nanocellulose.

[0020] S12. Add the modified nanocellulose to anhydrous ethanol, ultrasonically disperse for 20-25 min, stir and react at 50-55℃ for 2-2.5 h. After the reaction is complete, cool to room temperature and adjust the pH to 7-8 with sodium hydroxide solution to obtain the modified activator.

[0021] As a preferred embodiment of the present invention, the mass ratio of the modified activator to deionized water in step S1 is 1:(130-150), and the mass ratio of the modified activator to the nano-silica modified solvent in step S2 is 1:(0.6-0.8).

[0022] As a preferred embodiment of the present invention, in step S21, the mass ratio of silica initiator, acrylamide, catalytic system, and mixed solvent is 1:(8-12):(0.01-0.02):(80-100), wherein the catalytic system is composed of a mixture of cuprous bromide and pentamethyldiethylenetriamine in a mass ratio of 1:(1-1.22), and the mixed solvent is composed of anhydrous ethanol and deionized water in a mass ratio of 1:(3-4).

[0023] As a preferred embodiment of the present invention, in step S22, the mass ratio of modified silica intermediate, octyl acrylate hydrophobic monomer, and methanol is 1:(2-4):(20-25); in step S23, the mass ratio of silica graft, nanosheet aqueous dispersion, and anhydrous ethanol is 1:(0.2-0.4):(40-50).

[0024] As a preferred embodiment of the present invention, the mass ratio of nano-silica, ethanol, and 3-aminopropyltriethoxysilane in step S211 is 1:(15-20):(0.2-0.3).

[0025] As a preferred embodiment of the present invention, in step S212, the mass ratio of aminated silica, anhydrous ethanol, 2-bromoisobutyryl bromide, and triethylamine is 1:(15-20):(0.15-0.25):(0.2-0.3), wherein the dropping rate of triethylamine is set to 0.5-1.0 mL / min; in step S213, the mass ratio of ethanol, tetrahydrofuran, and the precipitate is (8-10):1.

[0026] As a preferred embodiment of the present invention, in step S11, the mass ratio of nanocellulose, anhydrous ethanol, and KH-570 is 1:(90-100):(0.1-0.15); in step S12, the mass ratio of anhydrous ethanol and modified nanocellulose is (40-50):(0.15-0.5).

[0027] As a preferred technical solution of the present invention, an oil displacement agent for oil extraction is prepared according to the preparation method described above.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. This invention utilizes a block structure grafted onto the surface of nano-silica to directionally distribute hydrophobic monomers at the ends of molecular chains, enabling the rapid formation of a high-strength, high-toughness interfacial film at the oil-water interface, significantly reducing interfacial interaction energy. Simultaneously, relying on the steric hindrance effect of the block structure, it forms reasonable flow control within the pores, inhibiting the cross-flow of oil displacement agents and expanding the swept volume. Modified nanoparticles and block polymers can enter micropores, relying on the strong exfoliation of adsorbed oil through the interfacial film. Furthermore, the reasonable particle size and spatial structure improve the flow state within the pores, enhancing adaptability to low-permeability, complex-pore reservoirs.

[0030] 2. In this invention, the fluorine-containing structure and zwitterionic structure can form a stable hydration layer in a salt ion environment to resist interference from calcium and magnesium ions; the modified nanocellulose and fluorine-containing nanosheets work synergistically to enable the oil displacement agent to maintain good dispersibility and interfacial activity in high-salinity formation water, breaking through the limitation that traditional oil displacement agents are only suitable for low-salinity oil reservoirs. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the preparation process of the oil displacement agent in this invention;

[0032] Figure 2 This is a schematic diagram of the preparation process of the nano-silica modified solvent in this invention;

[0033] Figure 3 This is a schematic diagram of the preparation process of the silica initiator in this invention;

[0034] Figure 4 This is a schematic diagram of the preparation process of the modified surfactant in this invention;

[0035] Figure 5 This is a schematic diagram of the preparation process of the nanosheet aqueous dispersion in this invention;

[0036] Figure 6 The image shows a transmission electron microscope image of the nanosheet aqueous dispersion prepared in Example 1.

[0037] Figure 7 This is a comparison diagram of the interfacial behavior of the oil displacement agent and simulated crude oil in Example 1 and Comparative Example 1. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0039] Please see Figures 1-7 This invention provides a technical solution for an oil displacement agent used in petroleum extraction and its preparation method:

[0040] Example 1:

[0041] A method for preparing an oil displacement agent for petroleum extraction includes the following steps:

[0042] I. Preparation of silica initiator:

[0043] S211. Take 10.0g of nano silica and add 150.0g of anhydrous ethanol to prepare a silica dispersion. Add 2.0g of 3-aminopropyltriethoxysilane and reflux at 78℃ for 5h. Wash with ethanol, centrifuge twice, and vacuum dry at 60℃ to obtain aminated silica.

[0044] S212. Take 10.0g of aminated silica, disperse it in 150.0g of anhydrous ethanol, add 1.5g of 2-bromoisobutyryl bromide, and add 2.0g of triethylamine dropwise at a rate of 0.5mL / min under 0℃ ice bath conditions. After the addition is complete, react at room temperature for 10h.

[0045] S213. After the reaction is complete, the precipitate is collected by centrifugation. Each 1g of precipitate is washed alternately with 8g of anhydrous ethanol and 8g of tetrahydrofuran, centrifuged 3 times, and dried under vacuum at 60℃ to obtain the silica initiator.

[0046] II. Preparation of modified surfactants:

[0047] S11. Take 5.0g of nanocellulose, add 450.0g of anhydrous ethanol, adjust the pH to 3 with dilute hydrochloric acid, stir for 10min to obtain a dispersion, dilute 0.5g of KH-570 with 10g of anhydrous ethanol and add it to the dispersion, react at 60℃ for 3h, centrifuge to collect the precipitate, wash twice with anhydrous ethanol, and dry to obtain modified nanocellulose.

[0048] S12. Take 15.0g of petroleum sulfonate and 5.0g of sodium lignosulfonate, add 200.0g of anhydrous ethanol, stir at 40℃ for 1h to obtain a mixed solution, add 0.75g of modified nanocellulose, ultrasonically disperse for 20min, stir at 50℃ for 2h, cool to room temperature and adjust pH to 7 with dilute sodium hydroxide solution to obtain the modified activator.

[0049] III. Preparation of solvents modified with nano-silica:

[0050] S21. Take 8.0g of silica initiator, 64.0g of acrylamide, and 0.08g of catalytic system (0.04g of cuprous bromide and 0.04g of pentamethyldiethylenetriamine), add 640.0g of mixed solvent (160.0g of anhydrous ethanol and 480.0g of deionized water), and deoxygenate by two cycles of liquid nitrogen freezing-vacuuming-thawing. Then, polymerize in a sealed environment at 60℃ for 6 hours to obtain the modified silica intermediate.

[0051] S22. In an oxygen-free atmosphere, add 16.0g of octyl acrylate hydrophobic monomer to 8g of modified silica intermediate, polymerize at 60℃ for 6h, add 160g of methanol to terminate the reaction and precipitate, wash the precipitate with ethanol 3 times and then vacuum dry to obtain silica graft.

[0052] S23. Mix 90g trifluorotoluene, 0.25g 4-cyano-4-(thiobenzoyl)valerate, 0.08g sodium bicarbonate and 100g deionized water. Heat to 30℃ under nitrogen protection. First, add 7g of fluorinated monomer dropwise and initiate the polymerization under UV light at a wavelength of 365nm and a power of 400W for 30min. Then, add 11g of zwitterionic monomer dropwise and continue UV initiation polymerization for 30min. After the reaction is completed, centrifuge and dialyze for 72h to obtain an aqueous dispersion of nanosheets. Take 10.0g of silica graft and disperse it in 400.0g of anhydrous ethanol. Add 2.0g of the aqueous dispersion of nanosheets and stir at room temperature for 2h to obtain a nano-silica modified solvent.

[0053] IV. Preparation of oil displacement agents:

[0054] S1. Take 3g of modified activator and add 390g of deionized water according to the ratio of modified activator to nano silica modified solvent = 1:0.6, stir until completely dispersed, and obtain an aqueous solution of activator.

[0055] S2. Add 1.8g of nano-silica modified solvent to the activator aqueous solution, stir for 30min, adjust the pH of the system to 7, and let it stand for 2h to obtain the oil displacement agent for oil extraction.

[0056] Example 2:

[0057] A method for preparing an oil displacement agent for petroleum extraction includes the following steps:

[0058] I. Preparation of silica initiator:

[0059] S211. Take 10.0g of nano-silica, add 175.0g of anhydrous ethanol to prepare a silica dispersion, add 2.5g of 3-aminopropyltriethoxysilane, reflux at 80℃ for 5.5h, wash with ethanol, centrifuge twice, and vacuum dry at 60℃ to obtain aminated silica.

[0060] S212. Take 10.0g of aminated silica and disperse it in 175.0g of anhydrous ethanol. Add 2.0g of 2-bromoisobutyryl bromide and add 2.5g of triethylamine dropwise at a rate of 0.75mL / min under ice bath conditions at 1℃. After the addition is complete, react at room temperature for 11h.

[0061] S213. After the reaction is complete, the precipitate is collected by centrifugation. Each 1g of precipitate is washed with 9g of anhydrous ethanol and 9g of tetrahydrofuran alternately, centrifuged 3 times, and dried under vacuum at 60℃ to obtain the silica initiator.

[0062] II. Preparation of modified surfactants:

[0063] S11. Take 5.0g of nanocellulose, add 475.0g of anhydrous ethanol, adjust the pH to 3.5 with dilute hydrochloric acid, stir for 12min to obtain a dispersion, dilute 0.625g of KH-570 with 10g of anhydrous ethanol and add it to the dispersion, react at 63℃ for 3.5h, collect the precipitate by centrifugation, wash 3 times with anhydrous ethanol, and dry to obtain modified nanocellulose.

[0064] S12. Take 17.5g of petroleum sulfonate and 5.0g of sodium lignosulfonate, add 225.0g of anhydrous ethanol, stir at 43℃ for 1.3h to obtain a mixed solution, add 1.625g of modified nanocellulose, ultrasonically disperse for 22min, stir at 53℃ for 2.3h, cool to room temperature and adjust the pH to 7.5 with dilute sodium hydroxide solution to obtain the modified activator.

[0065] III. Preparation of solvents modified with nano-silica:

[0066] S21. Take 8.0g of silica initiator, 80.0g of acrylamide, and 0.12g of catalytic system (0.057g of cuprous bromide and 0.063g of pentamethyldiethylenetriamine), add 720.0g of mixed solvent (160.0g of anhydrous ethanol and 560.0g of deionized water), and deoxygenate by three cycles of liquid nitrogen freezing-vacuuming-thawing. Then, polymerize in a sealed environment at 60℃ for 9h to obtain the modified silica intermediate.

[0067] S22. In an oxygen-free atmosphere, add 24.0g of octyl acrylate hydrophobic monomer to 8g of modified silica intermediate, polymerize at 63℃ for 8h, add 176g of methanol to terminate the reaction and precipitate, wash the precipitate with ethanol 3 times and then vacuum dry to obtain silica graft.

[0068] S23. Mix 100g trifluorotoluene, 0.3g 4-cyano-4-(thiobenzoyl)valerate, 0.1g sodium bicarbonate and 100g deionized water. Heat to 33℃ under nitrogen protection. First, add 8g of fluorinated monomer dropwise and initiate the polymerization with UV light at a wavelength of 365nm and a power of 400W for 35min. Then, add 12g of zwitterionic monomer dropwise and continue UV initiation polymerization for 35min. After the reaction is completed, centrifuge and dialyze for 84h to obtain an aqueous dispersion of nanosheets. Take 10.0g of silica graft and disperse it in 450.0g of anhydrous ethanol. Add 3.0g of the aqueous dispersion of nanosheets and stir at room temperature for 2.3h to obtain a nano-silica modified solvent.

[0069] IV. Preparation of oil displacement agents:

[0070] S1. Take 3g of modified activator and add 420g of deionized water according to the ratio of modified activator to nano silica modified solvent = 1:0.7, stir until completely dispersed, and obtain an aqueous solution of activator.

[0071] S2. Add 2.1g of nano-silica modified solvent to the activator aqueous solution, stir for 45min, adjust the pH of the system to 7.5, and let it stand for 3h to obtain the oil displacement agent for oil extraction.

[0072] Example 3:

[0073] A method for preparing an oil displacement agent for petroleum extraction includes the following steps:

[0074] I. Preparation of silica initiator:

[0075] S211. Take 10.0g of nano-silica, add 200.0g of anhydrous ethanol to prepare a silica dispersion, add 3.0g of 3-aminopropyltriethoxysilane, reflux at 82℃ for 6h, wash with ethanol, centrifuge 3 times, and vacuum dry at 60℃ to obtain aminated silica.

[0076] S212. Take 10.0g of aminated silica, disperse it in 200.0g of anhydrous ethanol, add 2.5g of 2-bromoisobutyryl bromide, and add 3.0g of triethylamine dropwise at a rate of 1.0mL / min under ice bath conditions at 2℃. After the addition is complete, react at room temperature for 12h.

[0077] S213. After the reaction is complete, the precipitate is collected by centrifugation. Each 1g of precipitate is washed alternately with 10g of anhydrous ethanol and 10g of tetrahydrofuran, centrifuged 3 times, and dried under vacuum at 60℃ to obtain the silica initiator.

[0078] II. Preparation of modified surfactants:

[0079] S11. Take 5.0g of nanocellulose, add 500.0g of anhydrous ethanol, adjust the pH to 4 with dilute hydrochloric acid, stir for 15min to obtain a dispersion, dilute 0.75g of KH-570 with 10g of anhydrous ethanol and add it to the dispersion, react at 65℃ for 4h, collect the precipitate by centrifugation, wash 3 times with anhydrous ethanol, and dry to obtain modified nanocellulose.

[0080] S12. Take 20.0g of petroleum sulfonate and 5.0g of sodium lignosulfonate, add 250.0g of anhydrous ethanol, stir at 45℃ for 1.5h to obtain a mixed solution, add 2.5g of modified nanocellulose, ultrasonically disperse for 25min, stir at 55℃ for 2.5h, cool to room temperature and adjust the pH to 8 with dilute sodium hydroxide solution to obtain the modified activator.

[0081] III. Preparation of solvents modified with nano-silica:

[0082] S21. Take 8.0g of silica initiator, 96.0g of acrylamide, and 0.16g of catalytic system (0.072g of cuprous bromide and 0.088g of pentamethyldiethylenetriamine), add 800.0g of mixed solvent (160.0g of anhydrous ethanol and 640.0g of deionized water), and deoxygenate by three cycles of liquid nitrogen freezing-vacuuming-thawing. Then, polymerize in a sealed environment at 65℃ for 12h to obtain a modified silica intermediate.

[0083] S22. In an oxygen-free atmosphere, add 32.0g of octyl acrylate hydrophobic monomer to 8g of modified silica intermediate, polymerize at 65℃ for 10h, add 200g of anhydrous methanol to terminate the reaction and precipitate, wash the precipitate three times with ethanol and then vacuum dry to obtain silica graft.

[0084] S23. Mix 110g trifluorotoluene, 0.35g 4-cyano-4-(thiobenzoyl)valerate, 0.12g sodium bicarbonate and 100g deionized water. Heat to 35℃ under nitrogen protection. First, add 9g of fluorinated monomer dropwise and initiate the polymerization with UV light at a wavelength of 365nm and a power of 400W for 40min. Then, add 13g of zwitterionic monomer dropwise and continue UV initiation polymerization for 40min. After the reaction is completed, centrifuge and dialyze for 96h to obtain an aqueous dispersion of nanosheets. Take 10.0g of silica graft and disperse it in 500.0g of anhydrous ethanol. Add 4.0g of the aqueous dispersion of nanosheets and stir at room temperature for 2.5h to obtain a nano-silica modified solvent.

[0085] IV. Preparation of oil displacement agents:

[0086] S1. Take 3g of modified activator and add 450g of deionized water according to the ratio of modified activator to nano silica modified solvent = 1:0.8, stir until completely dispersed, and obtain an aqueous solution of activator.

[0087] S2. Add 2.4g of nano-silica modified solvent to the activator aqueous solution, stir for 60min, adjust the pH of the system to 8, and let it stand for 4h to obtain the oil displacement agent for oil extraction.

[0088] Comparative Example 1:

[0089] Compared to Example 1, Comparative Example 1 replaced the nano-silica modified solvent with a solvent composed of anhydrous ethanol, nano-silica and polyacrylamide in a mass ratio of 1:0.4:0.1, while the remaining steps were exactly the same as in Example 1.

[0090] Comparative Example 2:

[0091] Comparative Example 2 differs from Example 1 in that the nano-silica initiator is replaced with an equal mass of nano-silica, while the remaining steps are exactly the same as in Example 1.

[0092] Comparative Example 3:

[0093] Compared to Example 1, Comparative Example 3 replaced the modified activator with an activator composed of petroleum sulfonate and sodium lignin sulfonate in a mass ratio of 1:0.6, while the remaining steps were exactly the same as in Example 1.

[0094] I. Oil-water interfacial tension testing

[0095] The pendant drop method was used to capture the droplet morphology formed by the oil displacement agent and simulated crude oil using an interfacial tensiometer, and the interfacial tension of the oil-water two phases was calculated. The lower the interfacial tension, the stronger the stripping and emulsification ability of the oil displacement agent on the crude oil.

[0096] Take the oil displacement agents from Examples 1-3 and Comparative Examples 1-3 respectively, dilute them with simulated reservoir formation water to 0.5wt% (the actual concentration used on site), stir evenly, and let stand for 10 minutes to obtain the oil displacement agent solution to be tested. Take 20mL of the oil displacement agent solution to be tested and add it to the sample bottle. Insert the capillary of the interfacial tension meter into the solution, and use a pipette to draw 5μL of simulated crude oil and squeeze it out from the tip of the capillary to form a stable droplet. Start the instrument to calculate the interfacial tension and continuously detect it for 30 minutes. Record the equilibrium interfacial tension (mN / m).

[0097] II. Oil Displacement Efficiency Testing

[0098] Artificial core displacement experiments were used to simulate reservoir formation conditions and determine the remaining oil recovery rate after water flooding and displacement by the oil displacement agent. The oil displacement efficiency = (mass of crude oil displaced by the oil displacement agent / original oil content of the core) × 100%. The higher the value, the better the actual oil recovery effect.

[0099] A piece of material is 30cm long, 2.5cm in diameter, with a porosity of 30%-35% and a permeability of 50×10⁻⁶. -3 μm2 The core was vacuumed for 4 hours, saturated with simulated formation water, and the saturated water volume was recorded. The core pore volume (PV) was calculated. Simulated crude oil was injected into the core at a rate of 0.1 mL / min until no water droplets flowed out of the core outlet. The injected crude oil volume was recorded, and the original oil content of the core was calculated. Simulated formation water was injected into the core at a rate of 0.2 mL / min until no crude oil flowed out of the outlet. The mass of crude oil removed by water displacement was recorded, and the water drive recovery rate was calculated. Maintaining a displacement rate of 0.2 mL / min, 1.0 PV of the test oil displacement agent was injected into the core. After injection, the outlet was closed, and the well was shut off for 24 hours. Then, simulated formation water was injected again at a rate of 0.2 mL / min until no crude oil flowed out of the outlet. The total mass of crude oil removed by the oil displacement agent plus subsequent water displacement was recorded. The specific test results are shown in Table 1 below.

[0100] Table 1: Test Table of Interfacial Tension and Oil Displacement Efficiency of Oil Displacement Agents

[0101] Implementation Interfacial tension (mN / m) Oil displacement efficiency (%) Example 1 <![CDATA[3.2×10 -4 ]]> 58.6 Example 2 <![CDATA[2.7×10 -4 ]]> 60.3 Example 3 <![CDATA[3.5×10 -4 ]]> 57.8 Comparative Example 1 <![CDATA[8.6×10 -2 ]]> 35.2 Comparative Example 2 <![CDATA[1.5×10 -3 ]]> 42.5 Comparative Example 3 <![CDATA[9.8×10 -4 ]]> 48.3

[0102] As can be seen from the data in Table 1, the oil displacement agents prepared in Examples 1-3 of this invention are significantly better than those in Comparative Examples 1-3 in terms of interfacial tension and oil displacement efficiency. Example 2 exhibits the best overall performance, indicating that after block grafting and modification of nanocellulose, the oil displacement agent can significantly reduce the oil-water interfacial tension and possess stronger crude oil emulsification and stripping capabilities. Regarding oil displacement efficiency, all examples achieved over 57.8%, with Example 2 reaching a maximum of 60.3%, while the highest among the comparative examples was only 48.3%. This demonstrates that the structural design of this invention effectively improves the swept volume and oil washing efficiency. Comparative Example 1, lacking grafting modification, had the worst interfacial activity and oil displacement effect. Comparative Example 2, lacking an initiator, resulted in insufficient grafting and a significant decrease in performance. Comparative Example 3, without modified nanocellulose, had weaker interfacial tension and oil displacement efficiency than the examples. Overall, this indicates that high-density grafting on the nano-silica surface, hydrophobic monomer end positioning, and the combination of modified activators are key to improving oil displacement performance.

[0103] III. System Stability Testing

[0104] By conducting high-temperature static and centrifugation acceleration experiments, we can observe whether the oil displacement agent system exhibits stratification, precipitation, or agglomeration, thereby determining its storage stability and on-site compatibility. The longer the stability period, the stronger its practicality.

[0105] 1. Take 20 mL of the oil displacement agent stock solution of Examples 1-3 and Comparative Examples 1-3 respectively, add it to a stoppered graduated test tube, seal it and let it stand at room temperature; observe the state of the system on days 1, 7, 30 and 60 respectively, and record whether there is layering, precipitation, floating oil or agglomeration. Determine the stable period: the longest standing time without obvious changes is the room temperature stable period.

[0106] 2. Take 20 mL of the oil displacement agent stock solution to be tested and add it to a stoppered graduated test tube. After sealing, place it in a 60℃ constant temperature drying oven. Take it out on the 1st, 7th, 30th and 60th days respectively, cool it to room temperature and observe the state of the system. Record the longest time without stratification and precipitation as the high temperature stability period.

[0107] 3. Take 10 mL of the oil displacement agent stock solution to be tested and add it to a centrifuge tube. Place the tube in a high-speed centrifuge and centrifuge at 8000 r / min for 30 min. After taking it out, observe whether the system separates into layers or precipitates. If there is no obvious separation and the precipitation volume is ≤0.5%, the system is centrifugally stable; otherwise, it is unstable.

[0108] IV. Salt Tolerance Test

[0109] Simulated formation water with different salt concentrations was prepared, and the interfacial tension and system stability were tested after diluting the oil displacement agent. The performance retention ability of the oil displacement agent in a high-salt environment was determined. The higher the salt concentration tolerance, the wider the range of oil reservoir types it is suitable for.

[0110] Salt solutions with concentrations of 10000, 20000, 30000, and 40000 mg / L were prepared. The oil displacement agent to be tested was diluted to 0.5 wt% with salt solutions of different concentrations and labeled as sample 1, 2, 3, and 4, respectively. After stirring evenly, the solutions were allowed to stand for 10 min. The equilibrium interfacial tension of the oil displacement agent at each salt concentration was measured (according to the oil-water interfacial tension test method). The appearance of the oil displacement agent system at each salt concentration was observed, and the highest salt concentration at which no stratification, precipitation, or agglomeration occurred was recorded as the salt tolerance threshold for system stability. The specific test results are shown in Table 2 below.

[0111] Table 2: Stability and Salt Tolerance Test Table of Oil Displacement Agents

[0112]

[0113] As can be seen from the data in Table 2, the system stability and salt tolerance of Examples 1-3 of this invention are comprehensively superior to those of Comparative Examples 1-3, with Example 2 showing the most outstanding performance. This indicates that the modified grafting and compounding can significantly inhibit particle agglomeration and stratification. In the centrifugation test, none of the examples showed stratification, while the comparative examples showed varying degrees of stratification, verifying that the system compatibility is better. In terms of salt tolerance, Example 2 has a stable salt tolerance threshold of 40,000 mg / L, Examples 1 and 3 can reach 30,000 mg / L, while the comparative examples only reach a maximum of 20,000 mg / L. This shows that the present invention can maintain interfacial activity and system stability in high-salt reservoir environments. Comparative Example 1 has the worst stability and salt tolerance due to the lack of modified structure. Comparative Example 2 did not use an initiator, so the particles were prone to agglomeration and had weak salt tolerance. Comparative Example 3 lacked modified nanocellulose, so its salt resistance and stabilization effects were limited. In summary, the present invention, through silica-initiated grafting, block structure design, and modified nanocellulose compounding, significantly improves the long-term storage, high-temperature adaptability, and high-salt tolerance of the oil displacement agent, which can meet the needs of complex reservoirs.

[0114] Figure 6 The images show transmission electron microscopy (TEM) images of the nanosheet aqueous dispersion prepared in Example 1. These images visually represent the microstructure, size, and dispersion state of the nanosheets. As can be seen from the images, the nanosheets exhibit a uniform two-dimensional sheet structure with regular morphology, clear edges, and no obvious breakage, curling, or large-area stacking. The individual sheets are uniform in size and relatively thin, consistent with the typical characteristics of nanosheets formed by the copolymerization of fluorinated monomers and zwitterionic monomers. The nanosheets show excellent dispersibility in the aqueous dispersion system, with no obvious agglomeration or clumping. The interparticle spacing is moderate and the distribution is uniform, demonstrating that trifluorotoluene and 4... cyano-4-(thiobenzoyl)valerate, sodium bicarbonate, and other raw materials can efficiently complete the copolymerization reaction under nitrogen protection and ultraviolet initiation conditions to form a stable nanosheet structure. At the same time, the nanosheets are free of obvious impurities and impurities, and have good crystallinity and structural integrity, indicating that the centrifugation and dialysis purification steps effectively remove unreacted monomers and by-products. This microstructure ensures that the nanosheets can be stably dispersed in the anhydrous ethanol and silica graft system, providing a good foundation for the subsequent preparation of nano-silica modified solvents, and also providing structural support for improving the interfacial activity, salt resistance and stability of oil displacement agents.

[0115] Figure 7 The diagram shows a comparison of the interfacial behavior of the oil displacement agent in Example 1 and Comparative Example 1 with simulated crude oil. It clearly reflects the difference in their effects at the oil-water interface. In Example 1 (corresponding to 2 in the diagram), after the oil displacement agent comes into contact with crude oil, the interface spreads rapidly, the interfacial layer is blurred but uniform in thickness, and the crude oil is quickly emulsified and dispersed, forming a stable oil-water mixture system without obvious stratification or crude oil aggregation. This indicates that it can significantly reduce interfacial tension, efficiently remove adsorbed crude oil from the rock surface, and possesses excellent oil washing and emulsification capabilities. In contrast, after the oil displacement agent in Comparative Example 1 (corresponding to 1 in the diagram) comes into contact with crude oil, the interface is clearly defined, and the crude oil exhibits... Agglomerated aggregates are difficult to emulsify and disperse, the interface layer is rough and easily shrinks, the system quickly separates into oil and water, and the interfacial activity is extremely poor. In comparison, Example 1, due to the use of nano-silica graft modification and the combination of modified activator, can form a dense adsorption layer at the interface, which significantly reduces the interfacial tension. Comparative Example 1, without graft modification, is only a simple compound system and cannot effectively change the interfacial properties, making it difficult for crude oil to be activated. This interfacial behavior directly corresponds to the difference in oil displacement efficiency. Example 1 has a stronger interfacial effect and a better oil displacement effect, verifying the key role of the modification process of this invention in improving the interfacial performance of the oil displacement agent.

[0116] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.

Claims

1. A method for preparing an oil displacement agent for petroleum extraction, characterized in that, Includes the following steps: S1. Add the modified surfactant to deionized water and stir until completely dispersed to obtain an aqueous surfactant solution; S2. Add the nano-silica modified solvent to the activator aqueous solution, stir for 30-60 min, adjust the pH to 7-8, and let it stand for 2-4 h to obtain the oil displacement agent; In step S1, the mass ratio of the modified surfactant to deionized water is 1:(130-150), and the mass ratio of the modified surfactant to the nano-silica modified solvent in step S2 is 1:(0.6-0.8). The nano-silica modified solvent is prepared through the following steps: S21. Add silica initiator, acrylamide, and catalytic system to a mixed solvent, and deoxygenate by liquid nitrogen freezing, vacuuming, and thawing cycles 2-3 times. Polymerize at 60-65℃ for 6-12 hours to obtain modified silica intermediate. S22. In an oxygen-free atmosphere, add octyl acrylate hydrophobic monomer to the modified silica intermediate and polymerize at 60-65℃ for 6-10 hours. Add methanol to terminate the reaction and precipitate. Wash and dry the precipitate to obtain silica graft. S23. Disperse the silica graft in anhydrous ethanol, add the nanosheet aqueous dispersion, and stir for 2-2.5 h to obtain a nano-silica modified solvent. In step S21, the mass ratio of silica initiator, acrylamide, catalytic system, and mixed solvent is 1:(8-12):(0.01-0.02):(80-100). The catalytic system is composed of a mixture of cuprous bromide and pentamethyldiethylenetriamine in a mass ratio of 1:(1-1.22). The mixed solvent is composed of anhydrous ethanol and deionized water in a mass ratio of 1:(3-4). In step S22, the mass ratio of modified silica intermediate, octyl acrylate hydrophobic monomer, and methanol is 1:(2-4):(20-25). In step S23, the mass ratio of silica graft, nanosheet aqueous dispersion, and anhydrous ethanol is 1:(0.2-0.4):(40-50). The nanosheet aqueous dispersion is prepared through the following steps: Trifluorotoluene, 4-cyano-4-(thiobenzoyl)valerate, sodium bicarbonate, and deionized water are mixed and heated to 30-35°C under nitrogen protection. The fluorinated monomer CH2=C(R) is then added dropwise. 1 COOCH2CH2(CF2) n F, n=6, R 1 =H or CH2, UV initiation for 30-40 min at a wavelength of 365 nm and a power of 400 W, followed by dropwise addition of the zwitterionic monomer CH2=C(R) 2 COO(CH2)2N + (R 3 (R) 4 (CH2) m SO3 - m=8, R 2 =H or CH3, R 3 R 4 Each is an independent C1-C3 alkyl group. The polymerization was continued under UV initiation for 30-40 min. After the reaction was completed, the mixture was centrifuged and dialyzed for 72-96 h to obtain an aqueous dispersion of nanosheets. The mass ratio of trifluorotoluene, 4-cyano-4-(thiobenzoyl)valerate, sodium bicarbonate, fluorinated monomer, zwitterionic monomer and deionized water is (90-110):(0.25-0.35):(0.08-0.12):(7-9):(11-13):100; The silica initiator in step S21 is prepared through the following steps: S211. Nano silica and ethanol are mixed to prepare a silica dispersion. 3-aminopropyltriethoxysilane is added and the mixture is refluxed at 78-82℃ for 5-6 hours. After washing with ethanol and centrifuging 2-3 times, the aminated silica is obtained by vacuum drying. S212. Aminated silica is dispersed in anhydrous ethanol, 2-bromoisobutyryl bromide is added as an initiator precursor, and triethylamine is added dropwise at 0-2℃. The reaction is carried out at room temperature for 10-12 h. S213. After the reaction is complete, the precipitate is collected by centrifugation. The precipitate is washed with ethanol and tetrahydrofuran alternately and then centrifuged. The washed precipitate is then dried under vacuum to obtain the silica initiator. In step S211, the mass ratio of nano-silica, ethanol, and 3-aminopropyltriethoxysilane is 1:(15-20):(0.2-0.3). The modified surfactant in step S1 is prepared through the following steps: S11. Add nanocellulose to anhydrous ethanol, adjust the pH to 3-4 with dilute hydrochloric acid, stir for 10-15 min to obtain a dispersion, add KH-570 to the dispersion, react at 60-65℃ for 3-4 h, after the reaction is completed, centrifuge to collect the precipitate, wash the precipitate 2-3 times with anhydrous ethanol to obtain modified nanocellulose. S12. Take petroleum sulfonate and sodium lignosulfonate, add anhydrous ethanol, stir to obtain a mixed solution, then add modified nanocellulose, ultrasonically disperse for 20-25 min, stir and react at 50-55℃ for 2-2.5 h, after the reaction is completed, cool to room temperature, adjust the pH to 7-8 with sodium hydroxide solution to obtain the modified activator. In step S11, the mass ratio of nanocellulose, anhydrous ethanol, and KH-570 is 1:(90-100):(0.1-0.15).

2. The method for preparing an oil displacement agent for petroleum extraction according to claim 1, characterized in that: In step S212, the mass ratio of aminated silica, anhydrous ethanol, 2-bromoisobutyryl bromide, and triethylamine is 1:(15-20):(0.15-0.25):(0.2-0.3), wherein the dropping rate of triethylamine is set to 0.5-1.0 mL / min. In step S213, the mass ratio of ethanol, tetrahydrofuran, and precipitate is (8-10):

1.

3. An oil displacement agent for petroleum extraction, characterized in that, The oil displacement agent for oil extraction is prepared according to the preparation method described in any one of claims 1-2.

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