Salt-tolerant oil displacement system for alkali-free binary combination flooding and preparation method and application thereof

Abstract

The application relates to a salt-resistant oil displacement system for alkali-free binary compound flooding and a preparation method and application thereof, and belongs to the technical field of oil production. The oil displacement system is composed of the following components: 0.1-0.5 wt% of amino silane coupling agent modified xanthan gum, 0.1-0.5 wt% of a surfactant, 0.05-0.2 wt% of a high-temperature stabilizer, 0.05-0.1 wt% of chitosan quaternary ammonium salt, 0.05-0.1 wt% of silane coupling agent modified nano silicon dioxide, and the balance of water; the high-temperature stabilizer is one or more of polyvinyl alcohol, polyethylene glycol and polypropylene glycol. The oil displacement system provided by the application is compounded by taking xanthan gum as a core compound and a surfactant, is an oil displacement system for alkali-free binary compound flooding, utilizes the high-salt resistance of xanthan gum, and improves the defects of poor water solubility, easy decomposition at high temperature and easy degradation by bacteria, and has obvious improvement in profile control performance and can be used in a high-salt high-temperature environment.

Description

Technical Field

[0001] This application relates to an alkali-free binary composite flooding salt-tolerant oil displacement system, its preparation method and application, belonging to the field of oil production technology. Background Technology

[0002] Polymer flooding involves adding polymers to the aqueous phase to increase water viscosity, reduce the water-to-oil mobility ratio, and decrease the relative permeability of water, thereby adjusting the water absorption profile and increasing the swept volume of the aqueous phase. The polymer solution is a viscoelastic fluid; the tensile deformation and viscoelastic effect it generates cause residual oil that is difficult to be swept away in pores and fissures to become fibrous or piston-like in the channels and be displaced by the polymer solution, thus improving oil washing efficiency. However, in high-temperature, high-salinity reservoirs, polymer molecules are prone to coiling, leading to a weakened mobility control capability.

[0003] Partially hydrolyzed polyacrylamide (HPAM) is the most widely used synthetic polymer. Its raw materials are readily available, the synthesis method is simple, low-cost, and easy to industrialize. It also possesses good thickening properties, making it the most widely used polymer in polymer flooding applications. However, HPAM is highly susceptible to degradation and viscosity loss in porous media due to environmental factors such as high temperature, high mineralization, and microbial activity. Furthermore, it exhibits poor resistance to high salt and high temperatures.

[0004] like Figure 1 The natural polymer xanthan gum shown is a high-molecular-weight biopolysaccharide that has a double helix structure at low temperatures. However, as the temperature rises, the double helix structure gradually becomes a disordered helix, indicating that it is not resistant to high temperatures. However, xanthan gum has better high-salt resistance than HPAM. Xanthan gum is more stable than HPAM at higher mineralization levels, so it is more suitable for high-salt conditions. However, both xanthan gum and HPAM are prone to degradation under high-temperature conditions.

[0005] Compared to HPAM, xanthan gum has less application in polymer flooding. Existing patent CN111849447B discloses a method for modifying xanthan gum and a modified xanthan gum flooding agent. This method uses a phenylboronic acid polymer to modify xanthan gum, improving its viscosity, resistance to aging and degradation, and resistance to interference from ethylene glycol and 1,3-propanediol. However, it does not pay much attention to the performance requirements of the flooding agent in high-salt and high-temperature environments. Furthermore, it still suffers from the problem of xanthan gum being easily degraded by formation bacteria during use.

[0006] Therefore, it is necessary to provide an oil displacement system using xanthan gum as a polymer and alkali-free binary composite material under high salinity and high temperature conditions to improve the oil displacement effect. Summary of the Invention

[0007] To address the aforementioned issues, an alkali-free binary composite flooding system for salt-tolerant oil displacement, its preparation method, and its application are provided. This oil displacement system uses xanthan gum as the core complex and is compounded with surfactants. It is an alkali-free binary composite flooding system that utilizes the high salt tolerance of xanthan gum. Furthermore, it has been improved to address the shortcomings of xanthan gum, such as poor water solubility, easy decomposition at high temperatures, and susceptibility to microbial influences. This makes it adaptable to high-temperature and high-salt environments and exhibits good oil displacement performance, especially with significant improvements in profile control performance.

[0008] This application provides an alkali-free binary composite flooding system for salt-resistant oil displacement, characterized in that the oil displacement system is composed of the following components: 0.1~0.5wt% aminosilane coupling agent modified xanthan gum, 0.1~0.5wt% surfactant, 0.05~0.2wt% high temperature stabilizer, 0.05~0.1wt% chitosan quaternary ammonium salt, 0.05~0.1wt% silane coupling agent modified nano-silica, and the balance being water;

[0009] The high-temperature stabilizer is one or more of polyvinyl alcohol, polyethylene glycol, and polypropylene glycol.

[0010] Optionally, the aminosilane coupling agent in the aminosilane coupling agent modified xanthan gum is a bisaminosilane coupling agent;

[0011] The bis(amino)silane coupling agent is selected from one or more of N-β-aminoethyl-γ-aminopropyltrimethoxysilane, bis(γ-trimethoxysilyl)amine, and N-phenyl-γ-aminopropyltrimethoxysilane.

[0012] Optionally, the preparation method of the aminosilane coupling agent modified xanthan gum includes the steps of adding water to xanthan gum and stirring evenly, and then adding 2-5 wt% of aminosilane coupling agent to xanthan gum and stirring to react.

[0013] Optionally, the silane coupling agent modified nano-silica is γ-(methacryloyloxy)propyltrimethoxysilane modified nano-silica.

[0014] Optionally, the preparation method of the γ-(methacryloyloxy)propyltrimethoxysilane modified nano-silica includes:

[0015] Nano-silica was added to water and uniformly dispersed to obtain a silica suspension. After adding acidified γ-(methacryloyloxy)propyltrimethoxysilane to the silica suspension, the mixture was heated under reflux to obtain the γ-(methacryloyloxy)propyltrimethoxysilane-modified nano-silica.

[0016] Optionally, the molecular weight of the chitosan quaternary ammonium salt is 200,000 to 500,000; and / or,

[0017] The xanthan gum raw material has a molecular weight of 3 million to 5 million; and / or,

[0018] The average particle size of the nano-silica raw material is 100~300 nm; and / or,

[0019] The molecular weight of the high-temperature stabilizer is 10,000 to 30,000.

[0020] Optionally, the surfactant is selected from one or more of tetradecyl dipropyl hydroxypropanesulfonate betaine, hexadecyl dipropyl carboxybetaine, or octadecyl dipropyl hydroxypropanesulfonate betaine.

[0021] This application provides a method for preparing the above-mentioned alkali-free binary composite flooding salt-resistant oil displacement system. The preparation method includes the step of dissolving xanthan gum modified with aminosilane coupling agent, surfactant, high-temperature stabilizer, chitosan quaternary ammonium salt, and nano-silica modified with silane coupling agent in water to prepare a mixed solution.

[0022] This application provides the application of the above-mentioned alkali-free binary composite flooding salt-resistant oil displacement system in reservoir oil displacement.

[0023] Optionally, the reservoir temperature is ≥100℃ and the water salinity is ≥100000 mg / L.

[0024] The beneficial effects of this application include, but are not limited to:

[0025] 1. According to the alkali-free binary composite flooding salt-resistant oil displacement system, its preparation method and application, a high-temperature stabilizer is added in combination with chitosan quaternary ammonium salt and aminosilane coupling agent modified xanthan gum. The high-temperature stabilizer can improve the high-temperature resistance of xanthan gum, thereby reducing the impact of high-temperature degradation. The chitosan quaternary ammonium salt can bring antibacterial effect, reduce the degradation effect of bacteria on aminosilane coupling agent modified xanthan gum, so that the oil displacement system has high salt resistance, high temperature resistance and antibacterial degradation resistance.

[0026] 2. According to the alkali-free binary composite flooding salt-resistant oil displacement system and its preparation method and application in this application, xanthan gum is modified with aminosilane coupling agents, especially bis(γ-trimethoxysilylpropyl)amine, N-phenyl-γ-aminopropyltrimethoxysilane and other bisaminosilane coupling agents. Among them, the amino group has potential antibacterial effect, and the -OH generated after the methoxy group is hydrolyzed reacts with the hydroxyl group on the xanthan gum molecular chain, which has strong hydrophilicity and easily adsorbs water molecules, thereby improving its solubility. In addition, the surface activity of xanthan gum is improved due to the interaction between the methoxy group and the hydroxyl group after the methoxy group is hydrolyzed, thereby improving its compatibility with high temperature stabilizers and chitosan quaternary ammonium salts, and also improving its high temperature resistance and antibacterial effect.

[0027] 3. Based on the alkali-free binary composite flooding salt-resistant oil displacement system, its preparation method, and its application, silane coupling agent-modified nano-silica is further added to the system. On the one hand, the modified nano-silica has good compatibility with aminosilane coupling agent-modified xanthan gum, which has a certain effect on improving the high-temperature resistance of aminosilane coupling agent-modified xanthan gum. In addition, the harder silane coupling agent-modified nano-silica, combined with high molecular polymers such as aminosilane coupling agent-modified xanthan gum, high-temperature stabilizers, and chitosan quaternary ammonium salt, can more easily plug the large pores in the oil well during oil displacement, thereby facilitating the oil displacement effect in small pores and showing a significant improvement in profile control performance.

[0028] 4. According to the alkali-free binary composite flooding salt-resistant oil displacement system of this application, its preparation method and application, the surfactant selected is a betaine surfactant with a large molecular weight such as tetradecyl dipropyl hydroxypropanesulfonate betaine, hexadecyl dipropyl carboxybetaine or octadecyl dipropyl hydroxypropanesulfonate betaine. Combined with a high temperature stabilizer, it has a good high temperature resistance effect. In addition, the large-head betaine has good compatibility with cationic chitosan quaternary ammonium salt and high interfacial activity, which can significantly reduce the oil-water interfacial tension.

[0029] 5. According to the alkali-free binary composite flooding salt-resistant oil displacement system of this application, its preparation method and application, the use of γ-(methacryloyloxy)propyltrimethoxysilane to modify nano-silica can effectively improve the aggregation between silica particles, which is beneficial to its dispersibility. Moreover, it has good compatibility with aminosilane coupling agent modified xanthan gum, which is beneficial to its improvement of the high temperature resistance of aminosilane coupling agent modified xanthan gum. Attached Figure Description

[0030] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0031] Figure 1 This is a schematic diagram of the molecular structure of xanthan gum involved in this application. Detailed Implementation

[0032] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments. Unless otherwise specified, the raw materials and reagents in the embodiments of the present application are all purchased through commercial channels.

[0033] Example 1

[0034] An alkali-free binary composite oil displacement system is provided, comprising the following components: 0.4 wt% N-β-aminoethyl-γ-aminopropyltrimethoxysilane-modified xanthan gum, 0.5 wt% octadecyl dipropylhydroxypropanesulfonyl betaine, 0.1 wt% polyvinyl alcohol, 0.1 wt% chitosan quaternary ammonium salt, 0.05 wt% γ-(methacryloyloxy)propyltrimethoxysilane-modified nano silica, with the balance being water;

[0035] The preparation process of this oil displacement system is as follows:

[0036] 1) Preparation of N-β-aminoethyl-γ-aminopropyltrimethoxysilane modified xanthan gum: Add 10 g of xanthan gum (molecular weight 3 million to 5 million) to a beaker, then add 20 mL of water and stir well. Then add 5 wt% of N-β-aminoethyl-γ-aminopropyltrimethoxysilane, stir well, and dry in a desiccator to obtain N-β-aminoethyl-γ-aminopropyltrimethoxysilane modified xanthan gum for later use.

[0037] 2) Preparation of γ-(methacryloyloxy)propyltrimethoxysilane modified nano-silica: Add 100 mL of isopropanol to a beaker, adjust the pH to 5.0 with acetic acid, add 20 mL of water and stir well, then add 5 g of γ-(methacryloyloxy)propyltrimethoxysilane and stir well for later use; take another beaker and add 20 g of nano-silica powder (average particle size of 286 nm) and an appropriate amount of water, and use ultrasonic vibration to uniformly disperse to obtain a silica suspension for later use; slowly add the solution containing γ-(methacryloyloxy)propyltrimethoxysilane to the silica suspension, and reflux at 70℃ for 1 h; after the reaction is complete, filter the product, wash it 2-3 times with ethanol, and dry it in an oven at 105℃ until the weight basically no longer changes, to obtain γ-(methacryloyloxy)propyltrimethoxysilane modified nano-silica for later use;

[0038] 3 g of unmodified nano-silica was added to 100 mL of paraffin liquid. After ultrasonic dispersion and standing for 5 days, sedimentation was observed. 3 g of γ-(methacryloyloxy)propyltrimethoxysilane-modified nano-silica was added to 100 mL of paraffin liquid. After ultrasonic dispersion under the same conditions and standing for 20 days, no sedimentation was observed, indicating that the organic compatibility of γ-(methacryloyloxy)propyltrimethoxysilane-modified silica was improved.

[0039] 3) First, add the prescribed amount of water. While stirring, add the prescribed amounts of N-β-aminoethyl-γ-aminopropyltrimethoxysilane-modified xanthan gum, octadecyl dipropylhydroxypropanesulfonyl betaine, polyvinyl alcohol (molecular weight 10,000~30,000), chitosan quaternary ammonium salt (molecular weight 200,000~500,000), and γ-(methacryloyloxy)propyltrimethoxysilane-modified nano silica to the water in sequence. After stirring evenly, the alkali-free binary composite oil displacement system is obtained.

[0040] Example 2

[0041] An alkali-free binary composite oil displacement system is provided, comprising the following components: 0.5 wt% bis(γ-trimethoxysilylpropyl)amine modified xanthan gum, 0.3 wt% hexadecyl dipropyl carboxylic betaine, 0.2 wt% polyethylene glycol, 0.1 wt% chitosan quaternary ammonium salt, 0.1 wt% γ-(methacryloyloxy)propyltrimethoxysilane modified nano silica, with the balance being water;

[0042] The preparation process of this oil displacement system is as follows:

[0043] 1) Preparation of bis(γ-trimethoxysilylpropyl)amine modified xanthan gum: Add 10 g of xanthan gum (molecular weight 3 million to 5 million) to a beaker, then add 20 mL of water and stir well. Then add 3 wt% of bis(γ-trimethoxysilylpropyl)amine, stir well, and dry in a desiccator to obtain bis(γ-trimethoxysilylpropyl)amine modified xanthan gum for later use.

[0044] 2) Preparation of γ-(methacryloyloxy)propyltrimethoxysilane modified nano-silica: Add 100 mL of isopropanol to a beaker, adjust the pH to 5.0 with acetic acid, add 20 mL of water and stir well, then add 5 g of γ-(methacryloyloxy)propyltrimethoxysilane and stir well for later use; take another beaker and add 20 g of nano-silica powder (average particle size of 286 nm) and an appropriate amount of water, and use ultrasonic vibration to uniformly disperse to obtain a silica suspension for later use; slowly add the solution containing γ-(methacryloyloxy)propyltrimethoxysilane to the silica suspension, and reflux at 70℃ for 1 h; after the reaction is complete, filter the product, wash it 2-3 times with ethanol, and dry it in an oven at 105℃ until the weight basically no longer changes, to obtain γ-(methacryloyloxy)propyltrimethoxysilane modified nano-silica for later use;

[0045] 3 g of unmodified nano-silica was added to 100 mL of paraffin liquid. After ultrasonic dispersion and standing for 5 days, sedimentation was observed. 3 g of γ-(methacryloyloxy)propyltrimethoxysilane-modified nano-silica was added to 100 mL of paraffin liquid. After ultrasonic dispersion under the same conditions and standing for 20 days, no sedimentation was observed, indicating that the organic compatibility of γ-(methacryloyloxy)propyltrimethoxysilane-modified silica was improved.

[0046] 3) First, add the prescribed amount of water. While stirring, add the prescribed amounts of bis(γ-trimethoxysilylpropyl)amine modified xanthan gum, hexadecyl dipropyl carboxylic betaine, polyethylene glycol (molecular weight 10,000~30,000), chitosan quaternary ammonium salt (molecular weight 200,000~500,000), and γ-(methacryloyloxy)propyltrimethoxysilane modified nano silica to the water in sequence. After stirring evenly, the alkali-free binary composite oil displacement system is obtained.

[0047] Example 3

[0048] An alkali-free binary composite oil displacement system is provided, comprising the following components: 0.1 wt% N-β-aminoethyl-γ-aminopropyltrimethoxysilane-modified xanthan gum, 0.1 wt% tetradecyl dipropylhydroxypropanesulfonyl betaine, 0.05 wt% polypropylene glycol, 0.05 wt% chitosan quaternary ammonium salt, 0.05 wt% γ-(methacryloyloxy)propyltrimethoxysilane-modified nano silica, with the balance being water;

[0049] The preparation process of this oil displacement system is as follows:

[0050] 1) Preparation of N-phenyl-γ-aminopropyltrimethoxysilane modified xanthan gum: Add 10 g of xanthan gum (molecular weight 3 million to 5 million) to a beaker, then add 20 mL of water and stir well. Then add 2 wt% of N-phenyl-γ-aminopropyltrimethoxysilane, stir well, and dry in a desiccator to obtain N-phenyl-γ-aminopropyltrimethoxysilane modified xanthan gum for later use.

[0051] 2) Preparation of γ-(methacryloyloxy)propyltrimethoxysilane modified nano-silica: Add 100 mL of isopropanol to a beaker, adjust the pH to 5.0 with acetic acid, add 20 mL of water and stir well, then add 5 g of γ-(methacryloyloxy)propyltrimethoxysilane and stir well for later use; take another beaker and add 20 g of nano-silica powder (average particle size of 286 nm) and an appropriate amount of water, and use ultrasonic vibration to uniformly disperse to obtain a silica suspension for later use; slowly add the solution containing γ-(methacryloyloxy)propyltrimethoxysilane to the silica suspension, and reflux at 70℃ for 1 h; after the reaction is complete, filter the product, wash it 2-3 times with ethanol, and dry it in an oven at 105℃ until the weight basically no longer changes, to obtain γ-(methacryloyloxy)propyltrimethoxysilane modified nano-silica for later use;

[0052] 3 g of unmodified nano-silica was added to 100 mL of paraffin liquid. After ultrasonic dispersion and standing for 5 days, sedimentation was observed. 3 g of γ-(methacryloyloxy)propyltrimethoxysilane-modified nano-silica was added to 100 mL of paraffin liquid. After ultrasonic dispersion under the same conditions and standing for 20 days, no sedimentation was observed, indicating that the organic compatibility of γ-(methacryloyloxy)propyltrimethoxysilane-modified silica was improved.

[0053] 3) First, add the prescribed amount of water. While stirring, add the prescribed amounts of N-phenyl-γ-aminopropyltrimethoxysilane-modified xanthan gum, tetradecyl dipropylhydroxypropanesulfonyl betaine, polypropylene glycol (molecular weight 10,000~30,000), chitosan quaternary ammonium salt (molecular weight 200,000~500,000), and γ-(methacryloyloxy)propyltrimethoxysilane-modified nano silica to the water in sequence. After stirring evenly, the alkali-free binary composite oil displacement system is obtained.

[0054] Comparative Example 1

[0055] This comparative example is basically the same as Example 1, except that it does not contain chitosan quaternary ammonium salt.

[0056] Comparative Example 2

[0057] This comparative example is basically the same as Example 1, except that it does not contain polyvinyl alcohol.

[0058] Comparative Example 3

[0059] This comparative example is basically the same as Example 1, except that the silane coupling agent modified nano-silica is replaced with an equal amount of unmodified nano-silica.

[0060] Comparative Example 4

[0061] This comparative example is basically the same as Example 1, except that the aminosilane coupling agent modified xanthan gum is replaced with unmodified xanthan gum.

[0062] Test Example 1

[0063] Core-assisted oil recovery experiment: The artificial core dimensions were φ3.0*40 (cm), with a permeability of 2.87 μm. 2 The core samples had a porosity of 32.7%, a pore volume of 53.27 mL, an oil saturation of 78.2%, and a salinity of 100,000 mg / L. At 95℃, the core was vacuum-saturated with water and oil, aged for 24 h, and then subjected to water flooding. Once the water cut exceeded 98%, chemical flooding and subsequent water flooding were performed until no more oil was produced at the production end. The degree of oil recovery (%) was calculated based on the recovery rate at 98% water cut.

[0064] Viscosity measurement: at a temperature of 95℃ and a shear rate of 7.0 s⁻¹. -1 Under the specified conditions, the viscosity of the oil displacement system under test was determined using a rotational viscometer (DV-Ⅱ+Pro type rotational viscometer, Brookfield).

[0065] Oil-water interfacial tension measurement: Dehydrated crude oil from Shengli ST Oilfield, density (25℃) 0.982 g / cm³. 3 Viscosity (80℃) 18.52 mPa·s, freezing point -12.0℃, wax content 9.8%, gum and asphaltene content 12.8%. The oil-water interfacial tension was measured using a Texa-500 spin drop interfacial tension meter after being added to the oil displacement system to be tested at a test temperature of 95℃.

[0066] The test results of the example and comparative oil displacement systems are shown in Table 1 below.

[0067] Table 1. Test results of the oil displacement systems in the examples and comparative examples.

[0068]

[0069] As shown in Table 1, the oil displacement system provided in this application can significantly improve the oil-water interfacial tension under high salt and high temperature conditions, and has a good oil displacement effect.

[0070] According to the results of Comparative Example 1, the addition of chitosan quaternary ammonium salt can not only improve the antibacterial properties of xanthan gum and reduce bacterial degradation of xanthan gum, but also improve the recovery rate when used in combination with other components.

[0071] According to the comparison of the results of Comparative Example 2, the addition of polyvinyl alcohol can significantly improve the high temperature resistance of the oil displacement system, reduce the degradation of xanthan gum, thereby improving the degree of oil recovery, and maintain the solution viscosity well, which has a good effect on improving the oil-water interfacial tension.

[0072] According to the comparison of the results of Comparative Example 3, it can be seen that by modifying nano-silica, the compatibility of nano-silica with other components can be improved, especially the degree of recovery improvement is significantly improved. Modified nano-silica is easy to form polymer particles with water-blocking and profile control properties by modifying xanthan gum, chitosan quaternary ammonium salt, high temperature stabilizer, etc. with aminosilane coupling agent. Among them, hard nano-silica is more likely to block the large pores of the bottom layer during oil displacement, thus making it more conducive to the exploitation of oil reservoirs in small pores.

[0073] According to the results of Comparative Example 4, it can be seen that by modifying xanthan gum, its compatibility with high-temperature stabilizers, silane coupling agents modified nano-silica and chitosan quaternary ammonium salt can be improved, thereby improving the high-temperature resistance and antibacterial properties of xanthan gum, and facilitating the formation of polymer particles with blocking and profile control properties, thus improving the recovery rate and the oil-water interfacial tension is better improved.

[0074] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A salt-resistant oil displacement system for alkali-free binary composite flooding, characterized in that, The oil displacement system consists of the following components: 0.1-0.5 wt% aminosilane coupling agent modified xanthan gum, 0.1-0.5 wt% surfactant, 0.05-0.2 wt% high temperature stabilizer, 0.05-0.1 wt% chitosan quaternary ammonium salt, 0.05-0.1 wt% silane coupling agent modified nano silica, and the balance being water; The surfactant is selected from one or more of tetradecyl dipropyl hydroxypropanesulfonate betaine, hexadecyl dipropyl carboxybetaine, or octadecyl dipropyl hydroxypropanesulfonate betaine; The high-temperature stabilizer is one or more of polyvinyl alcohol, polyethylene glycol, and polypropylene glycol; The preparation method of the aminosilane coupling agent modified xanthan gum includes the steps of adding water to xanthan gum and stirring evenly, and then adding 2-5 wt% of aminosilane coupling agent to xanthan gum and stirring to react. The aminosilane coupling agent is one or more of N-β-aminoethyl-γ-aminopropyltrimethoxysilane, bis(γ-trimethoxysilylpropyl)amine, and N-phenyl-γ-aminopropyltrimethoxysilane. The silane coupling agent modified nano-silica is γ-(methacryloyloxy)propyltrimethoxysilane modified nano-silica. The preparation method of the γ-(methacryloyloxy)propyltrimethoxysilane modified nano-silica includes: adding nano-silica to water and dispersing it uniformly to obtain a silica suspension; adding acidified γ-(methacryloyloxy)propyltrimethoxysilane to the silica suspension; and then heating and refluxing to obtain the γ-(methacryloyloxy)propyltrimethoxysilane modified nano-silica.

2. The alkali-free binary composite flooding salt-resistant oil displacement system according to claim 1, characterized in that, The chitosan quaternary ammonium salt has a molecular weight of 200,000 to 500,000; and / or, The xanthan gum raw material has a molecular weight of 3 million to 5 million; and / or, The average particle size of the nano-silica raw material is 100~300 nm; and / or, The molecular weight of the high-temperature stabilizer is 10,000 to 30,000.

3. The preparation method of the alkali-free binary composite flooding salt-resistant oil displacement system as described in claim 1 or 2, characterized in that, The preparation method includes the step of dissolving xanthan gum modified with aminosilane coupling agent, surfactant, high temperature stabilizer, chitosan quaternary ammonium salt, and nano-silica modified with silane coupling agent in water to prepare a mixed solution.

4. The application of the alkali-free binary composite flooding salt-resistant oil displacement system as described in claim 1 or 2 in reservoir oil displacement.

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