A shale oil carbon dioxide flooding surfactant and its preparation method

Abstract

The present application discloses a shale oil carbon dioxide flooding surfactant and its preparation method, belonging to the field of surfactant technology. The shale oil carbon dioxide flooding surfactant comprises, by weight, 100 parts of water, 40-60 parts of a fluorinated copolymer, 15-25 parts of sodium dodecylbenzene sulfonate, 10-20 parts of a silicone-containing polyoxyethylene ether surfactant, and 5-10 parts of nanoparticles. By compounding the fluorinated copolymer with sodium dodecylbenzene sulfonate, the silicone-containing polyoxyethylene ether surfactant, and the nanoparticles, the surfactant has high salt and temperature resistance to adapt to the environment of shale oil reservoirs. On the other hand, it synergistically improves surface activity, reduces interfacial tension, changes rock surface wettability, and enhances system stability, thereby achieving a higher recovery rate.

Description

Technical Field

[0001] The present application relates to a shale oil carbon dioxide flooding surfactant and a preparation method thereof, belonging to the technical field of surfactants. Background Art

[0002] Shale reservoirs usually have poor physical properties, extremely small pores and throats, and shale oil exists in a complex form in the formation, usually in a high-temperature, high-pressure, and high-salt environment. Conventional water injection, chemical injection, thermal oil recovery, microbial oil recovery and other measures often fail to achieve good development results.

[0003] CO2 injection huff-and-puff oil recovery technology is a development technology widely used to improve the recovery rate of low-permeability oil reservoirs and tight oil reservoirs. Gas injection development can effectively improve reservoir physical properties, reduce reservoir crude oil viscosity, and expand the volume of crude oil. Compared with water drive, gas injection development has become an important measure to effectively improve the recovery rate of shale oil reservoirs.

[0004] To improve recovery, various additives are often used to assist CO2 in further enhancing oil recovery. Surfactants are among the most commonly used additives. On the one hand, upon contact with CO2, surfactants generate a large amount of foam in situ, which can selectively block high-permeability channel flow, improve formation heterogeneity, and expand the swept volume. On the other hand, surfactants can also reduce interfacial tension, emulsify and disperse crude oil, and reduce heavy oil viscosity during oil recovery. For example, the surfactants disclosed in patent CN105257264A include silane surfactants and polyether surfactants. The selected silane surfactants and polyether surfactants can reduce the minimum miscibility pressure between CO2 and the original phase, thereby improving the original recovery factor. However, these surfactants are only suitable for conventional oil reservoirs. In the unique high-temperature, high-pressure, and high-salinity environments of shale oil reservoirs, the effectiveness of these surfactants is significantly reduced, making it difficult to meet the requirements of shale oil recovery. Therefore, a surfactant that matches them is needed to meet the requirements of shale oil CO2 flooding. Summary of the Invention

[0005] In order to solve the above problems, a shale oil carbon dioxide flooding surfactant and a preparation method thereof are provided. The shale oil carbon dioxide flooding surfactant is prepared by compounding a fluorine-containing copolymer with sodium dodecylbenzene sulfonate, a silicone-containing polyoxyethylene ether surfactant and nanoparticles. On the one hand, the surfactant has high salt resistance and temperature resistance to adapt to the environment of shale oil reservoirs; on the other hand, it synergistically improves surface activity, reduces interfacial tension, changes rock surface wettability, enhances system stability and expands oil displacement swept volume, thereby achieving a higher recovery rate.

[0006] According to one aspect of the present application, a shale oil carbon dioxide flooding surfactant is provided, which comprises, by weight, 100 parts of water, 40-60 parts of a fluorinated copolymer, 15-25 parts of sodium dodecylbenzenesulfonate, 10-20 parts of a polyoxyethylene ether surfactant containing a silyl group, and 5-10 parts of nanoparticles;

[0007] The nanoparticles include nano-silicon dioxide and nano-aluminum oxide, the nano-silicon dioxide includes modified nano-silicon dioxide and unmodified nano-silicon dioxide, and the modified nano-silicon dioxide is obtained by modification with a silane coupling agent;

[0008] The preparation method of the fluorine-containing copolymer comprises the following steps:

[0009] S01: Add diethylaminoethyl methacrylate, N-isopropylacrylamide and dodecafluoroheptyl methacrylate into a reaction vessel in sequence, add deionized water, stir evenly and heat to 60-80°C;

[0010] S02 was added to the reaction vessel to initiator, stirred under nitrogen atmosphere for 5-7 hours, and cooled to room temperature to obtain a crude product;

[0011] The crude product S03 was purified by dialysis and freeze-dried to obtain a fluorinated copolymer.

[0012] Specifically, by compounding the fluorinated copolymer with sodium dodecylbenzenesulfonate, silicone-containing polyoxyethylene ether surfactants and nanoparticles, the surfactant has high salt resistance and temperature resistance on the one hand, so as to adapt to the environment of shale oil reservoirs; on the other hand, it synergistically improves surface activity, reduces interfacial tension, changes the wettability of the rock surface, and enhances the stability of the system, thereby achieving a higher recovery rate.

[0013] Specifically, the fluoropolymer provided herein is formed by free radical polymerization of diethylaminoethyl methacrylate, N-isopropylacrylamide, and dodecafluoroheptyl methacrylate. The polymer chain incorporates an amino ester structure with certain reactivity and adjustable properties from diethylaminoethyl methacrylate, an amide structure from N-isopropylacrylamide, and a fluorocarbon chain structure from dodecafluoroheptyl methacrylate that enhances heat resistance and modifies surface properties. This results in high heat resistance and significant advantages for applications such as shale oil CO2 flooding.

[0014] Optionally, the molar ratio of diethylaminoethyl methacrylate to N-isopropylacrylamide is (3-5):1; the molar ratio of diethylaminoethyl methacrylate to dodecafluoroheptyl methacrylate is (1-3):1; the initiator is ammonium persulfate, and the mass of the initiator is 1-1.5% of the total mass of the monomers.

[0015] Specifically, the present application makes specific restrictions on the molar ratio of each monomer and the amount of initiator added to obtain a fluorine-containing polymer that meets the requirements.

[0016] Optionally, the mass ratio of the nano-silicon dioxide to the nano-aluminum oxide is (2-5):1.

[0017] Specifically, the present application uses nanoparticles to compound with various components. On the one hand, the nanoparticles can be adsorbed on the surface of rock pores, changing the surface properties of the rock, making it more hydrophilic, thereby reducing the amount of crude oil adsorbed on the rock surface, which is beneficial to the displacement of crude oil; it can also play a role in blocking hyperpermeability channels while enhancing the stability of the entire surfactant system; the synergistic effect of nanoparticles and surfactants can further reduce the oil-water interfacial tension.

[0018] Specifically, the present application uses a compound of nano-silica and nano-alumina. On the one hand, both have high chemical stability and thermal stability, and can be better integrated into the surfactant system, enhancing the stability of the system and preventing premature precipitation and agglomeration of surfactants and other components; on the other hand, they can change the pore structure and rock surface properties through adsorption, filling, etc., thereby improving the recovery rate of crude oil.

[0019] Optionally, the modified nano-silica is prepared by modifying silica with an aminosilane coupling agent.

[0020] Specifically, the present application modifies nano-silica by using an aminosilane coupling agent. On the one hand, it can improve its dispersibility and avoid agglomeration; on the other hand, it can enhance the interaction between the components. After the nano-silica particles are amino-modified, the amino groups on their surface can interact with the acidic groups in the fluorine-containing copolymer and the sulfonic acid groups of sodium dodecylbenzenesulfonate, thereby better stabilizing the system structure and enhancing the synergistic effect in reducing interfacial tension and other aspects.

[0021] The preparation method of modified nano-silica is as follows: nano-silica is dispersed in anhydrous ethanol to obtain a suspension, 3-aminopropyltriethoxysilane is added, stirred and dispersed evenly, and the temperature is raised to 60-80°C, and the reaction is carried out for 3-6 hours to obtain modified nano-silica.

[0022] Specifically, the mass ratio of nano-silica to 3-aminopropyltriethoxysilane is (3~6):1.

[0023] Specifically, the particle size of nano-silicon dioxide is 20-50 nm, and the particle size of nano-aluminum oxide is 50-100 nm.

[0024] Optionally, the preparation method of the polyoxyethylene ether surfactant containing silicone groups comprises the following steps:

[0025] S1: Add γ-glycidyloxypropyltrimethoxysilane and polyethylene glycol monomethyl ether into a reaction vessel, add a catalyst, stir, and react at 70-90°C under a nitrogen atmosphere for 3-5 hours;

[0026] S2: adding methanol to the reaction system, reacting at 70-90°C for 2-3 hours under a nitrogen atmosphere to obtain a crude product;

[0027] S3 is subjected to reduced pressure distillation, dialysis and concentration to obtain a polyoxyethylene ether surfactant containing a silicone group.

[0028] Specifically, a silane coupling reaction is first used to allow the silyl group of γ-glycidyloxypropyltrimethoxysilane (GPTMS) to react with the hydroxyl group of polyethylene glycol monomethyl ether (MPEG) to form an intermediate with silyl groups and polyoxyethylene ether chain segments while retaining the epoxy group; then an epoxy ring-opening reaction is carried out, and methanol is added to open the epoxy group, further increasing the hydrophilicity of the product and the flexibility of the molecular chain, thereby generating a crude product of polyoxyethylene ether surfactant containing silyl groups; finally, after post-processing and purification, low-boiling point impurities are first removed by vacuum distillation, and then unreacted small molecule raw materials and catalysts and other impurities are further removed by dialysis using a dialysis bag, ultimately obtaining a relatively pure polyoxyethylene ether surfactant containing silyl groups.

[0029] Optionally, the molar ratio of γ-glycidyloxypropyltrimethoxysilane to polyethylene glycol monomethyl ether is 1:(1-1.3); the mass of the catalyst is 0.5-1% of the total mass of γ-glycidyloxypropyltrimethoxysilane and polyethylene glycol monomethyl ether; and the molar ratio of methanol to polyethylene glycol monomethyl ether is (1-2):1.

[0030] Optionally, the catalyst comprises tetrabutylammonium hydroxide.

[0031] Specifically, tetrabutylammonium hydroxide can effectively catalyze the reaction between silyl groups and hydroxyl groups under mild reaction conditions, accelerate the reaction rate without introducing excessive impurities that affect product performance.

[0032] According to one aspect of the present application, a method for preparing the above-mentioned shale oil carbon dioxide flooding surfactant is also provided, comprising the following steps:

[0033] (1) Add the fluorinated copolymer into water and stir evenly;

[0034] (2) Add sodium dodecylbenzenesulfonate and polyoxyethylene ether surfactant containing silicone group in sequence and stir evenly;

[0035] (3) Ultrasonic dispersion of the nanoparticles in water to form a dispersion, adding the mixed solution in step (2), stirring, and homogenizing the mixture 2 to 3 times in a high-pressure homogenizer;

[0036] (4) Adjust the pH value, cool to room temperature, and filter to obtain the shale oil carbon dioxide flooding surfactant.

[0037] Optionally, the temperature of water in step (1) is 40-50°C.

[0038] Optionally, the pressure of the circulating homogenization in step (3) is 1000-2000 PSI; and the pH value in step (4) is 6-8.

[0039] Specifically, the homogenization treatment in step (3) can effectively disperse and mix the various components therein better, avoid uneven phenomena such as agglomeration and stratification, and thus make the prepared surfactant product have good and stable performance, so that it can play a better effect in the subsequent application in the shale oil carbon dioxide flooding process.

[0040] The beneficial effects of this application include but are not limited to:

[0041] 1. The shale oil CO2 flooding surfactant disclosed herein is formulated by compounding a fluorinated copolymer with sodium dodecylbenzenesulfonate, a silicone-containing polyoxyethylene ether surfactant, and nanoparticles. This surfactant, on the one hand, exhibits high salt and temperature tolerance, adapting to the shale oil reservoir environment; and, on the other hand, synergistically improves surface activity, reduces interfacial tension, enhances system stability, and expands the flooding volume, thereby achieving a higher oil recovery rate.

[0042] 2. The shale oil CO2 flooding surfactant provided herein comprises a fluoropolymer whose polymer chain includes an amino ester structure imparting certain reactivity and adjustable properties from diethylaminoethyl methacrylate, an amide structure contributed by N-isopropylacrylamide, and a fluorocarbon chain structure introduced by dodecafluoroheptyl methacrylate, which enhances temperature resistance and modifies surface properties. As a result, the fluoropolymer is not only CO2-sensitive but also exhibits advantages such as reduced surface tension, enhanced compatibility with CO2, and improved temperature resistance. The fluoropolymer and sodium dodecylbenzenesulfonate act synergistically to enhance oil displacement efficiency.

[0043] 3. The shale oil CO2 flooding surfactants described in this application, the siloxy-containing polyoxyethylene ether surfactants, due to their unique siloxy structure and polyoxyethylene ether chain segments, exhibit excellent compatibility with CO2 and excel in reducing interfacial tension and improving wettability. The synergistic effect of the nanoparticles and surfactants can, on the one hand, reduce the adhesion between the oil film and the rock, facilitating the detachment of oil droplets and improving oil displacement efficiency; and, on the other hand, help reduce oil-water interfacial tension and maintain system stability.

[0044] 4. The preparation method of the shale oil carbon dioxide flooding surfactant according to the present application is simple and easy to promote and apply on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0046] Figure 1 This is the H-NMR spectrum of the fluorinated copolymer involved in Example 1 of the present application.

[0047] Figure 2 This is the H-NMR spectrum of the polyoxyethylene ether surfactant containing silicone groups involved in Example 1 of the present application. DETAILED DESCRIPTION

[0048] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0049] Unless otherwise specified, the raw materials in the examples and comparative examples of the present application were purchased through commercial channels.

[0050] Unless otherwise specified, the methods used in the examples and comparative examples of this application are conventional methods in the prior art. The preparation method of the modified nano-silica involved in the following examples and comparative examples is as follows: disperse nano-silica in anhydrous ethanol to obtain a suspension, add 3-aminopropyltriethoxysilane, stir and disperse evenly, and heat to 70°C and react for 5 hours to obtain modified nano-silica. The mass ratio of nano-silica to 3-aminopropyltriethoxysilane is 5:1, and the particle size of nano-silica is 30nm; the particle size of nano-alumina involved in the following examples and comparative examples is 60nm.

[0051] Example 1

[0052] A method for preparing a shale oil carbon dioxide flooding surfactant comprises the following steps:

[0053] (1) Weigh each raw material by weight, add 40 parts of fluorinated copolymer to 100 parts of water at a temperature of 40°C, and stir evenly;

[0054] (2) Add 15 parts of sodium dodecylbenzenesulfonate and 10 parts of polyoxyethylene ether surfactant containing silicone group in sequence and stir evenly;

[0055] (3) Ultrasonic dispersion of 5 parts of nanoparticles in water to form a dispersion, and adding the mixed solution in step (2), wherein the nanoparticles include modified nano-silica and nano-alumina, and the mass ratio of modified nano-silica to nano-alumina is 2:1; after stirring, the mixture is homogenized twice in a high-pressure homogenizer at a pressure of 1000 PSI;

[0056] (4) Adjust the pH value to 6, cool to room temperature and filter to obtain a shale oil carbon dioxide flooding surfactant with a mass fraction of 30%.

[0057] The preparation method of the fluorine-containing copolymer comprises the following steps:

[0058] S01: Diethylaminoethyl methacrylate, N-isopropylacrylamide, and dodecafluoroheptyl methacrylate are sequentially added into a reaction vessel, deionized water is added, the mixture is stirred evenly, and the temperature is raised to 60°C; wherein the molar ratio of diethylaminoethyl methacrylate to dodecafluoroheptyl methacrylate is 1:1; and the molar ratio of diethylaminoethyl methacrylate to N-isopropylacrylamide is 3:1;

[0059] S02 is added into the reaction vessel as initiator ammonium persulfate, the mass of the initiator is 1% of the mass of the monomers,

[0060] The reaction was stirred under nitrogen atmosphere for 5 h, and then cooled to room temperature to obtain a crude product.

[0061] The crude product S03 was purified by dialysis and freeze-dried to obtain a fluorinated copolymer.

[0062] The preparation method of the polyoxyethylene ether surfactant containing silicone group comprises the following steps:

[0063] S1: adding γ-glycidyloxypropyltrimethoxysilane and polyethylene glycol monomethyl ether to a reaction vessel in a molar ratio of γ-glycidyloxypropyltrimethoxysilane to polyethylene glycol monomethyl ether of 1:1; adding a catalyst, tetrabutylammonium hydroxide, the mass of the catalyst being 0.5% of the total mass of γ-glycidyloxypropyltrimethoxysilane and polyethylene glycol monomethyl ether, stirring, and reacting at 70°C for 3 hours under a nitrogen atmosphere;

[0064] S2: adding methanol to the reaction system at a molar ratio of methanol to polyethylene glycol monomethyl ether of 1:1, and reacting at 70°C for 2 h under a nitrogen atmosphere to obtain a crude product;

[0065] S3 is subjected to reduced pressure distillation, dialysis and concentration to obtain a polyoxyethylene ether surfactant containing a silicone group.

[0066] refer to Figure 1 、 2 It can be seen that the fluorine-containing copolymer and the silicone-containing polyoxyethylene ether surfactant of the present application have been successfully synthesized.

[0067] Example 2

[0068] A method for preparing a shale oil carbon dioxide flooding surfactant comprises the following steps:

[0069] (1) Weigh all the raw materials by weight, add 60 parts of fluorinated copolymer to 100 parts of water at a temperature of 50°C, and stir evenly;

[0070] (2) Add 25 parts of sodium dodecylbenzenesulfonate and 20 parts of polyoxyethylene ether surfactant containing silicone group in sequence and stir evenly;

[0071] (3) Ultrasonic dispersion of 10 parts of nanoparticles in water to form a dispersion, and adding the mixed solution in step (2), wherein the nanoparticles include modified nano-silica and nano-alumina, and the mass ratio of modified nano-silica to nano-alumina is 5:1; after stirring, the mixture is homogenized three times in a high-pressure homogenizer at a pressure of 2000 PSI;

[0072] (4) The pH value was adjusted to 8, cooled to room temperature, and filtered to obtain a shale oil carbon dioxide flooding surfactant with a mass fraction of 30%.

[0073] The preparation method of the fluorine-containing copolymer comprises the following steps:

[0074] S01: Diethylaminoethyl methacrylate, N-isopropylacrylamide, and dodecafluoroheptyl methacrylate are sequentially added into a reaction vessel, deionized water is added, the mixture is stirred evenly, and the temperature is raised to 80°C; wherein the molar ratio of diethylaminoethyl methacrylate to dodecafluoroheptyl methacrylate is 3:1; and the molar ratio of diethylaminoethyl methacrylate to N-isopropylacrylamide is 5:1;

[0075] S02 Add initiator ammonium persulfate into the reaction vessel, the mass of the initiator is 1.5% of the mass of the monomers,

[0076] The reaction was stirred under nitrogen atmosphere for 7 h, and then cooled to reflux to room temperature to obtain a crude product;

[0077] The crude product S03 was purified by dialysis and freeze-dried to obtain a fluorinated copolymer.

[0078] The preparation method of the polyoxyethylene ether surfactant containing silicone group comprises the following steps:

[0079] S1: adding γ-glycidyloxypropyltrimethoxysilane and polyethylene glycol monomethyl ether to a reaction vessel in a molar ratio of γ-glycidyloxypropyltrimethoxysilane to polyethylene glycol monomethyl ether of 1:1.3; adding a catalyst, tetrabutylammonium hydroxide, the mass of the catalyst being 1% of the total mass of γ-glycidyloxypropyltrimethoxysilane and polyethylene glycol monomethyl ether, stirring, and reacting at 90°C under a nitrogen atmosphere for 5 hours;

[0080] S2: adding methanol to the reaction system at a molar ratio of methanol to polyethylene glycol monomethyl ether of 2:1, and reacting at 90°C for 3 h under a nitrogen atmosphere to obtain a crude product;

[0081] S3 is subjected to reduced pressure distillation, dialysis and concentration to obtain a polyoxyethylene ether surfactant containing a silicone group.

[0082] Example 3

[0083] A method for preparing a shale oil carbon dioxide flooding surfactant comprises the following steps:

[0084] (1) Weigh all the raw materials by weight, add 50 parts of fluorinated copolymer to 100 parts of water at a temperature of 45°C, and stir evenly;

[0085] (2) Add 20 parts of sodium dodecylbenzenesulfonate and 15 parts of polyoxyethylene ether surfactant containing silicone group in sequence and stir evenly;

[0086] (3) Ultrasonic dispersion of 7 parts of nanoparticles in water to form a dispersion, and adding the mixed solution in step (2), wherein the nanoparticles include modified nano-silica and nano-alumina, and the mass ratio of modified nano-silica to nano-alumina is 3:1; after stirring, the mixture is circulated and homogenized three times in a high-pressure homogenizer at a pressure of 1500 PSI;

[0087] (4) Adjust the pH value to 7, cool to room temperature and filter to obtain a shale oil carbon dioxide flooding surfactant with a mass fraction of 30%.

[0088] The preparation method of the fluorine-containing copolymer comprises the following steps:

[0089] S01: Diethylaminoethyl methacrylate, N-isopropylacrylamide, and dodecafluoroheptyl methacrylate are sequentially added into a reaction vessel, deionized water is added, the mixture is stirred evenly, and the temperature is raised to 70°C; wherein the molar ratio of diethylaminoethyl methacrylate to dodecafluoroheptyl methacrylate is 2:1; and the molar ratio of diethylaminoethyl methacrylate to N-isopropylacrylamide is 4:1;

[0090] S02 is added into the reaction vessel as initiator ammonium persulfate, the mass of the initiator is 1.2% of the mass of the monomers,

[0091] The reaction was stirred under nitrogen atmosphere for 6 h, and then cooled to reflux to room temperature to obtain a crude product;

[0092] The crude product S03 was purified by dialysis and freeze-dried to obtain a fluorinated copolymer.

[0093] The preparation method of the polyoxyethylene ether surfactant containing silicone group comprises the following steps:

[0094] S1: adding γ-glycidyloxypropyltrimethoxysilane and polyethylene glycol monomethyl ether to a reaction vessel in a molar ratio of γ-glycidyloxypropyltrimethoxysilane to polyethylene glycol monomethyl ether of 1:1.1; adding a catalyst, tetrabutylammonium hydroxide, in a mass of 0.7% of the total mass of γ-glycidyloxypropyltrimethoxysilane and polyethylene glycol monomethyl ether, stirring, and reacting at 80°C under a nitrogen atmosphere for 4 hours;

[0095] S2: adding methanol to the reaction system at a molar ratio of methanol to polyethylene glycol monomethyl ether of 1.5:1, and reacting at 80°C for 2.5 hours under a nitrogen atmosphere to obtain a crude product;

[0096] S3 is subjected to reduced pressure distillation, dialysis and concentration to obtain a polyoxyethylene ether surfactant containing a silicone group.

[0097] Example 4

[0098] The difference between Example 4 and Example 3 is that unmodified nano-silica is used to replace modified nano-silica in the nanoparticles, and the rest are the same.

[0099] Comparative Example 1

[0100] The difference between Comparative Example 1 and Example 3 is that the fluorine-containing copolymer is not included, and the rest are the same.

[0101] Comparative Example 2

[0102] The difference between Comparative Example 2 and Example 3 is that sodium dodecylbenzenesulfonate is not included, and the rest are the same.

[0103] Comparative Example 3

[0104] The difference between Comparative Example 3 and Example 3 is that nanoparticles are not included, and the rest are the same.

[0105] Comparative Example 4

[0106] The difference between Comparative Example 4 and Example 3 is that the fluorine-containing copolymer is 55 parts and the polyoxyethylene ether surfactant containing silicone group is not included, and the rest are the same.

[0107] Comparative Example 5

[0108] The difference between Comparative Example 5 and Example 3 is that the monomer dodecafluoroheptyl methacrylate is not included in the preparation process of the fluorine-containing copolymer, and the rest are the same.

[0109] Comparative Example 6

[0110] The difference between Comparative Example 6 and Example 3 is that the proportion of nanoparticles remains unchanged and only nano-aluminum oxide is included, and the rest are the same.

[0111] Test Example 1: Temperature and salt resistance test

[0112] 0.1 g of the shale oil CO2 flooding surfactants prepared in the Examples and Comparative Examples were weighed and dissolved in 100 mL of aqueous solutions of varying salinity. The solutions were allowed to stand at different temperatures for 72 hours, and the state of the solutions was observed. The test results are shown in Table 1.

[0113] Table 1 Test results of temperature and salt resistance

[0114]

[0115] It can be seen from Table 1 that Examples 1 to 3 are all capable of shale oil carbon dioxide flooding. The surfactant can withstand high temperatures exceeding 135°C and has a salinity greater than 25×10 4 mg / L of brine, the high temperature and salt resistance of Example 4, Comparative Example 5, and Comparative Example 1 are slightly reduced compared with Examples 1 to 3; the high temperature and salt resistance of Comparative Example 1 and Comparative Example 2 are significantly reduced compared with Examples 1 to 3. The reason for this is that Comparative Example 1 does not include a fluorinated copolymer, and Comparative Example 2 does not include sodium dodecylbenzenesulfonate. The lack of the synergistic effect of the fluorinated polymer and sodium dodecylbenzenesulfonate results in a significant reduction in their heat and salt resistance.

[0116] Test Example 2 Oil-water interfacial tension test

[0117] 0.1 g of the shale oil carbon dioxide flooding surfactant prepared in the above examples and comparative examples was weighed and dissolved in 100 mL of a shale oil with a salinity of 25×10 4 mg / L(20×10 4 The interfacial tension (IFT) of the shale oil was measured at 125°C using a spinning drop interfacial tensiometer in a brine solution containing 10000 mg / L NaCl, 30,000 mg / L CaCl₂, and 20,000 mg / L MgCl₂. The results are shown in Table 2.

[0118] Table 2 Oil-water interfacial tension test results

[0119]

[0120] It can be seen from Table 2 that the shale oil carbon dioxide flooding surfactant provided in the embodiment of the present application can be reduced to 10 -3 In the range of mN / m, the oil-water interfacial tension is the largest in Comparative Example 1. The reason for this is that it does not include a fluorine-containing copolymer, and the ability to reduce the surface tension is greatly reduced.

[0121] Test case 3: core huff-and-puff experiment

[0122] A long core flooding experiment was conducted using a sandfill tube with a length of 1000 mm and a diameter of 25.4 mm to determine the minimum miscible pressure and recovery factor of the system. The specific steps include:

[0123] (1) Adding the shale oil carbon dioxide flooding surfactants of the embodiment and the comparative example into a high-pressure closed container respectively;

[0124] (2) Liquid carbon dioxide is then pumped into a high-pressure sealed container, with the mass of the shale oil carbon dioxide flooding surfactant being 20% ​​of the mass of the liquid carbon dioxide. The container is then heated and pressurized to transform it into a supercritical state, and the pressure is controlled to reach the desired experimental pressure;

[0125] (3) Sand filling. Fill the core tube model with quartz sand of 80-120 mesh. Fill the core tube model with sand in small amounts and multiple times, and continuously tap the core tube to ensure that the sand is filled tightly.

[0126] (4) Vacuum and weigh. Vacuum the sand filling tube and weigh the dry weight of the core tube after 4 hours.

[0127] (5) Saturated water: saturate the sand-filled tube model with water, weigh the wet weight, and calculate the pore volume, porosity, and water permeability. If the permeability is between 1000mD and 1500mD, proceed to the next step; otherwise, repeat steps (1) and (2).

[0128] (6) Saturated oil: The oil sample was heated to the experimental temperature of 80 °C, and the sand-filled tube saturated with water was used to drive the oil into the water. The oil-saturated oil speed was 0.5 mL min -1 , until no water comes out;

[0129] (7) CO2 injection for oil displacement: Connect the instrument and place it in a constant temperature box. When the experimental temperature is reached, start the displacement experiment. Set the back pressure required for the experiment, open the valve of the high-pressure sealed container and the six-way valve, and keep the constant injection rate at 0.3 mL min -1 , every time 0.05PV is injected, the oil production and displacement pump reading are recorded, and the inlet and outlet pressures of the long core are collected by the pressure acquisition box. When the cumulative gas injection exceeds 1.2PV pore volume, the displacement is stopped;

[0130] (8) Cleaning the sand filling pipe: After the displacement experiment is completed, take out the sand and clean the sand filling pipe with petroleum ether for use in the next set of experiments.

[0131] The test results are shown in Table 3.

[0132] Table 3 Core huff-and-puff test results

[0133]

[0134] As can be seen from Table 3, Examples 1 to 3 can effectively reduce the miscible pressure. The supercritical carbon dioxide carries the shale oil carbon dioxide flooding surfactant to contact the crude oil, reducing the interfacial tension at the interface between the carbon dioxide and the crude oil, thereby reducing its minimum miscible pressure, making it easy for the injected carbon dioxide to form a miscible zone with the crude oil, achieving miscible oil recovery, and thus improving the recovery rate.

[0135] The shale oil carbon dioxide flooding surfactant provided in this application has good high temperature resistance and salt resistance, can withstand temperatures exceeding 135°C, and has a mineralization greater than 25×10 4 mg / L brine has high oil-water interfacial activity and can reduce the oil-water interfacial tension with shale oil to 10 -3 mN / m range, which can effectively reduce the viscosity of crude oil, oil-gas interfacial tension and minimum miscibility pressure in the core pores, making it easier for crude oil to flow out of the core pores. The oil recovery efficiency can reach more than 69%, and it can be applied to the development of high-temperature and high-salinity shale oil reservoirs.

[0136] The foregoing is merely an embodiment of the present application, and the scope of protection of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc. made within the technical ideas and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A shale oil carbon dioxide flooding surfactant, characterized in that: The composition comprises, by weight, 100 parts of water, 40-60 parts of a fluorine-containing copolymer, 15-25 parts of sodium dodecylbenzenesulfonate, 10-20 parts of a polyoxyethylene ether surfactant containing a silyl group, and 5-10 parts of nanoparticles; The nanoparticles include nano-silicon dioxide and nano-aluminum oxide, the nano-silicon dioxide includes modified nano-silicon dioxide and unmodified nano-silicon dioxide, and the modified nano-silicon dioxide is obtained by modification with a silane coupling agent; The preparation method of the fluorine-containing copolymer comprises the following steps: S01: Add diethylaminoethyl methacrylate, N-isopropylacrylamide and dodecafluoroheptyl methacrylate into a reaction vessel in sequence, add deionized water, stir evenly and heat to 60-80°C; S02 was added to the reaction vessel to initiator, stirred under nitrogen atmosphere for 5-7 hours, and cooled to room temperature to obtain a crude product; The crude product S03 was purified by dialysis and freeze-dried to obtain a fluorinated copolymer; The mass ratio of the nano-silica to the nano-alumina is (2-5):1; the modified nano-silica is prepared by modifying the silica with an aminosilane coupling agent; The preparation method of the polyoxyethylene ether surfactant containing silicone group comprises the following steps: S1: Add γ-glycidyloxypropyltrimethoxysilane and polyethylene glycol monomethyl ether into a reaction vessel, add a catalyst, stir, and react at 70-90°C under a nitrogen atmosphere for 3-5 hours; S2: adding methanol to the reaction system, reacting at 70-90°C for 2-3 hours under a nitrogen atmosphere to obtain a crude product; S3 is subjected to reduced pressure distillation, dialysis and concentration to obtain a polyoxyethylene ether surfactant containing a silicone group.

2. The shale oil carbon dioxide flooding surfactant according to claim 1, characterized in that The molar ratio of diethylaminoethyl methacrylate to N-isopropylacrylamide is (3-5):1; the molar ratio of diethylaminoethyl methacrylate to dodecafluoroheptyl methacrylate is (1-3):1; the initiator is ammonium persulfate, and the mass of the initiator is 1-1.5% of the total mass of the monomers.

3. The shale oil carbon dioxide flooding surfactant according to claim 1, characterized in that The molar ratio of γ-glycidyloxypropyltrimethoxysilane to polyethylene glycol monomethyl ether is 1:(1-1.3); the mass of the catalyst is 0.5-1% of the total mass of γ-glycidyloxypropyltrimethoxysilane and polyethylene glycol monomethyl ether; and the molar ratio of methanol to polyethylene glycol monomethyl ether is (1-2):

1.

4. The shale oil carbon dioxide flooding surfactant according to claim 1, characterized in that The catalyst includes tetrabutylammonium hydroxide.

5. The method for preparing a shale oil carbon dioxide flooding surfactant according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Add the fluorinated copolymer into water and stir evenly; (2) Add sodium dodecylbenzenesulfonate and polyoxyethylene ether surfactant containing silicone group in sequence and stir evenly; (3) Ultrasonic dispersion of the nanoparticles in water to form a dispersion, adding the mixed solution in step (2), stirring, and homogenizing the mixture 2 to 3 times in a high-pressure homogenizer; (4) Adjust the pH value, cool to room temperature, and filter to obtain the shale oil carbon dioxide flooding surfactant.

6. The method for preparing a shale oil carbon dioxide flooding surfactant according to claim 5, characterized in that: The temperature of water in step (1) is 40-50°C.

7. The method for preparing a shale oil carbon dioxide flooding surfactant according to claim 5, characterized in that: The pressure of the circulating homogenization in step (3) is 1000~2000PSI; the pH value in step (4) is 6~8.

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