Multi-component modified nano-SiO2 particles, method for constructing high-efficiency CO2 foaming agent, and CO2 foaming agent

Abstract

The present invention relates to a method for constructing a high-efficiency CO2 foaming agent using multi-componently modified nano-SiO2 particles, and a CO2 foaming agent. The nano-SiO2 particles are chemically modified in two steps to prepare heat-resistant and salt-resistant particles with foam stabilization properties. The particles are then combined with a low-concentration betaine and α-olefin sulfonate composite surfactant to construct a high-efficiency CO2 foaming agent. By subjecting the nano-SiO2 particles to "multi-component" modifications, such as chemical and physical modifications, the nano-SiO2 particles are adsorbed on the gas-liquid surface and closely arranged to form a strong interfacial film. The foaming system, consisting of the modified nano-SiO2 particles, the betaine surfactant, and the α-olefin sulfonate, produces a foaming agent at 80°C, 10 MPa, and a water salt content of 3×10 4 The half-life of CO2 foam formed under the conditions of 100 mg / L is more than 9 times higher than that of simple modified nanoparticles and more than 6 times higher than that of α-olefin sulfonate.

Description

Technical Field

[0001] The present invention relates to the technical field of enhanced oil recovery, and in particular to a multi-component modified nano-SiO2 particle suitable for medium-high temperature and medium-high salinity oil reservoirs, a method for constructing a high-efficiency CO2 foaming agent, and the CO2 foaming agent. Background Art

[0002] For low-permeability reservoirs where water injection is difficult, gas injection is an effective way to replenish formation energy. Injecting carbon dioxide into low-permeability reservoirs can effectively increase oil recovery while also achieving the goal of underground storage of carbon dioxide. However, due to the heterogeneity of the formation, the injection process can lead to the carbon dioxide entering through fractures or into formations with relatively high permeability but low oil saturation, reducing the formation's gas storage rate and weakening the CO2's effectiveness in enhancing oil recovery.

[0003] Foaming is an important method for inhibiting carbon dioxide gas cross-flow, and the key lies in the performance of the foaming agent. A good foaming agent has a high foaming rate and forms stable foam. Foam stability can be improved by optimizing the molecular structure of the surfactant, compounding surfactants with different molecular structures, and adding polymers to the foaming agent solution. In recent years, a popular method for improving foam stability is to stabilize the foam with nanoparticles, of which nano-SiO2 is the most commonly used particle. Ordinary nano-SiO2 contains a large number of hydroxyl groups on its surface, which is highly hydrophilic and not easily adsorbed to the gas-liquid interface. Only after modifying the particle surface to near neutral wettability can such particles form a highly elastic surface film at the gas-liquid interface, thereby achieving a good foam stabilization effect. Two types of modification methods have been developed. One is grafting, where silane coupling agents such as dimethyldimethoxysilane and dimethyldichlorosilane form covalent bonds with the numerous hydroxyl groups on the surface of nano-SiO2, thereby attaching hydrophobic groups to the nanoparticle surface. Examples include CN111171798A, CN112175600A, and CN113426367A. Controlling the degree of grafting can control the wettability of the particle surface. Grafted particles can stabilize foams alone or in combination with other surfactants. Another modification method involves mixing nano-SiO2 particles with a surfactant in an aqueous solution. The surfactant is then directed onto the particle surface through electrostatic attraction, hydrogen bonding, and other mechanisms, shifting the wettability of the particle surface from hydrophilic to neutral. (For example, see CN110540833A.)

[0004] By grafting nano-silica with silane coupling agents or adsorbing surfactants on nano-silica in aqueous solution, neutral wetting nano-silica with greatly improved foam stabilization performance can be formed. However, these nano-particles will quickly aggregate in brine containing calcium and magnesium ions due to the weakening of surface hydration. Therefore, these particles are difficult to migrate to deep formations and are unable to generate foam with CO2 in deep formations to regulate CO2 gas channeling. Summary of the Invention

[0005] In view of the above-mentioned status of the prior art, especially the problem that the effect of stabilizing CO2 foam with a single surfactant is not ideal and that nanoparticles are difficult to achieve both foam stabilization and temperature and salt resistance, the present invention proposes to chemically modify nano-SiO2 particles in two steps to make them have foam stabilization and temperature and salt resistance. The obtained multi-modified nano-SiO2 particles are compounded with a low-concentration betaine and α-olefin sulfonate composite surfactant to construct a high-efficiency CO2 foaming agent.

[0006] Therefore, an object of the present invention is to provide a multi-component modified nano-SiO2 particle and a preparation method thereof. After two-step chemical modification, the obtained nano-SiO2 particles not only have a foam stabilizing effect, but are also temperature and salt resistant.

[0007] The second object of the present invention is to provide a method for constructing a high-efficiency CO2 foaming agent, which can be constructed by compounding multi-modified nano-SiO2 particles with low-concentration betaine and α-olefin sulfonate composite surfactants.

[0008] The third object of the present invention is to provide a CO2 foaming agent system constructed by the above method.

[0009] The technical solution for achieving the above-mentioned invention object can be summarized as follows:

[0010] The invention discloses a multi-component modified nano-SiO2 particle, which is obtained by modifying nano-SiO2 particles with gamma-glycidyloxypropyltriethoxysilane and dimethyldiethoxysilane.

[0011] According to the present invention, preferably, the particle size of the nano-SiO2 is 10 to 100 nm, more preferably 10 to 15 nm.

[0012] According to the present invention, preferably, in the multi-modified nano-SiO2 particles, the content of γ-glycidyloxypropyltriethoxysilane is 5 to 15% of the mass of the nano-SiO2 particles, more preferably 10%;

[0013] According to the present invention, preferably, the content of dimethyldiethoxysilane in the multi-component modified nano-SiO2 particles is 1 to 3% of the mass of the nano-SiO2 particles, and more preferably 2%.

[0014] According to the present invention, preferably, the water phase wetting angle of the multi-modified nano-SiO2 particles is ≥40°.

[0015] According to the present invention, the method for preparing the multi-component modified nano-SiO2 particles comprises the following steps:

[0016] (1) Step 1 modification: reaction of nano-SiO2 particles with γ-glycidyloxypropyltriethoxysilane

[0017] Disperse nano-SiO2 particles in methanol, add γ-glycidoxypropyltriethoxysilane, and heat to 50-70°C for 8-12 hours;

[0018] (2) Step 2 modification: reaction of the modified product from step 1 with dimethyldiethoxysilane

[0019] Add dimethyltriethoxysilane to the modified product of step 1 and react at 50-70°C for 8-12 hours to obtain multi-component modified nano-SiO2 particles.

[0020] According to the present invention, the multi-component modified nano-SiO2 particles are used in a CO2 foaming agent system in the oil reservoir field.

[0021] According to the present invention, a method for constructing a high-efficiency CO2 foaming agent is also provided. The method comprises compounding the above-mentioned multi-modified nano-SiO2 particles with a betaine active agent and an α-olefin sulfonate composite surfactant.

[0022] According to the present invention, there is also provided a high-efficiency CO2 foaming agent constructed as above, comprising the following components in percentage by mass:

[0023] 0.1% to 1% multi-component modified nano-SiO2 particles, 0.01% to 0.1% betaine active agent, 0.01% to 0.3% α-olefin sulfonate, and the rest is water.

[0024] According to the present invention, preferably, the amount of the multi-component modified nano-SiO2 particles in the foaming agent is 0.2 to 0.6% of the mass of the foaming agent.

[0025] According to the present invention, preferably, the α-olefin sulfonate in the foaming agent is C 14-16 The amount of AOS, α-olefin sulfonate, used is 0.05-0.1% of the mass of the foaming agent.

[0026] According to the present invention, preferably, the betaine active agent in the foaming agent is at least one of cocamidopropyl betaine, oleamidopropyl betaine, and erucamidopropyl betaine, and oleamidopropyl betaine is most preferred;

[0027] Preferably, the amount of betaine active agent used is 20-40% of the concentration of α-olefin sulfonate, more preferably 30-35%.

[0028] The beneficial effects of the present invention are as follows:

[0029] 1. The particles used for foam stabilization must be able to continuously migrate in the formation to adjust the gas mobility in the deep reservoir. The salt content of oilfield water is generally greater than 5×103 mg / L, the poor stability of conventional nanoparticles in oilfield water restricts their practical application in oilfields. The multi-modified nano-SiO2 particles modified in two steps of the present invention can be heated to 80°C and with a salt content of 3×10 4 The nanoparticles were stable in water for more than 30 days at a concentration of 100 mg / L, meeting the requirements for nanoparticle migration to deep reservoirs. Unmodified nanoparticles, however, were stable for less than a day under the same conditions.

[0030] 2. The present invention has established a method for stabilizing foam by using nanoparticles and surfactants. The CO2 foaming agent is not only stable but also temperature and salt resistant. The CO2 foaming agent system composed of multi-component modified nano-SiO2 particles, betaine surfactant, and α-olefin sulfonate is stable at 80°C, 10MPa, and a salt content of 3×10 4 The half-life of CO2 foam formed under the conditions of 100 mg / L is more than 9 times higher than that of simple modified nanoparticles and more than 6 times higher than that of simple surfactant α-olefin sulfonate. DETAILED DESCRIPTION

[0031] The present invention proposes to prepare temperature-resistant and salt-resistant particles with foam stabilizing effect by chemically modifying nano-SiO2 particles in two steps, and to construct a high-efficiency CO2 foaming agent with a composite surfactant of low-concentration betaine and α-olefin sulfonate.

[0032] The multi-component modified nano-SiO2 particles of the present invention are obtained by modifying nano-SiO2 particles with gamma-glycidyloxypropyltriethoxysilane (KH561 coupling agent) and dimethyldiethoxysilane.

[0033] According to the present invention, the multi-component modified nano-SiO2 particles are obtained by two-step chemical modification, and the preparation method comprises the following steps:

[0034] (1) Step 1 modification: reaction of nano-SiO2 particles with γ-glycidyloxypropyltriethoxysilane

[0035] Disperse nano-SiO2 particles in methanol, add γ-glycidoxypropyltriethoxysilane (hereinafter referred to as modifier 1), and heat to 50-70°C for 8-12 hours;

[0036] In the first step of the modification process, the γ-glycidyloxypropyltriethoxysilane coupling agent reacts with the hydroxyl groups on the surface of the SiO2 particles and bonds to the SiO2 surface. At the same time, the epoxy groups at the end of the coupling agent molecules gradually open to form vicinal diols. These vicinal diol-containing groups have good water solubility and can prevent Ca 2+ Mg 2+ It reacts with the hydroxyl groups on the surface of SiO2 particles, thereby improving the temperature and salt resistance of nano-SiO2 particles.

[0037] (2) Step 2 modification: reaction of the modified product from step 1 with dimethyldiethoxysilane

[0038] Add dimethyltriethoxysilane to the modified product of step 1 and react at 50-70°C for 8-12 hours to obtain multi-component modified nano-SiO2 particles.

[0039] To control the water wetting angle on the surface of the nano-SiO2 particles, dimethyltriethoxysilane (hereinafter referred to as Modifier 2) is added to the modified product from Step 1 for a modification reaction. Dimethyltriethoxysilane reacts with the remaining hydroxyl groups on the surface of the nano-SiO2 particles and bonds to the particle surface, thereby increasing the particle surface wetting angle.

[0040] According to the present invention, the particles modified in the above two steps can be distributed on the gas-liquid surface to stabilize the foam. The higher the amount of modifier 1 added, the better the temperature and salt resistance of the modified nanoparticles. However, if the amount of modifier 1 added exceeds 15% of the mass of the nano-SiO2 particles, the residual hydroxyl content on the surface of the nano-SiO2 particles will decrease, which will affect the progress of the second step grafting reaction.

[0041] Therefore, in one or more preferred embodiments, in the multinarily modified nano-SiO2 particles, the content of γ-glycidyloxypropyltriethoxysilane is 5 to 15% of the mass of the nano-SiO2 particles, preferably 10%.

[0042] According to the present invention, the higher the amount of modifier 2 added, the more methyl groups are grafted onto the surface of the nano-SiO2 particles, and the larger the water phase wetting angle on the surface of the nano-SiO2 particles. However, if the amount of modifier 2 added exceeds 3% of the mass of the nano-SiO2 particles, the stability of the nano-SiO2 particles in salt water will be significantly reduced.

[0043] Therefore, in one or more preferred embodiments, the amount of the modifier 2 added is 1 to 3% of the mass of the nano-SiO2 particles, preferably 2%.

[0044] In one or more preferred embodiments, the particle size of the nano-SiO2 is 10 to 100 nm, preferably 10 to 15 nm.

[0045] In one or more preferred embodiments, the water wetting angle of the multi-modified nano-SiO2 particles is ≥40°.

[0046] A preferred preparation embodiment of the multi-component modified nano-SiO2 particles comprises the following steps:

[0047] (1) Step 1 modification: reaction of nano-SiO2 particles with γ-glycidyloxypropyltriethoxysilane

[0048] Weigh 10 grams of nano-SiO2 particles and add them to a three-necked flask equipped with a stirrer. Then add 90 grams of methanol and stir vigorously for 10 minutes to fully disperse the particles. Then add 0.5-1.5 grams of γ-glycidyl ether propyl triethoxysilane to the three-necked flask, stir for 10 minutes, and then heat to 60°C and react for 10 hours.

[0049] (2) Step 2 modification: reaction of the modified product from step 1 with dimethyldiethoxysilane

[0050] Add 0.1-0.5 g of dimethyltriethoxysilane to the modified product of step 1, and react at 60° C. with stirring for 10 h to obtain multi-component modified nano-SiO 2 particles.

[0051] According to the present invention, the multi-component modified nano-SiO2 particles are used in a CO2 foaming agent system in the oil reservoir field.

[0052] According to the present invention, a method for constructing a high-efficiency CO2 foaming agent is also provided. The method comprises compounding the above-mentioned multi-modified nano-SiO2 particles with a betaine active agent and an α-olefin sulfonate composite surfactant.

[0053] According to the present invention, there is also provided a high-efficiency CO2 foaming agent constructed as above, comprising the following components in percentage by mass:

[0054] 0.1% to 1% multi-component modified nano-SiO2 particles, 0.01% to 0.1% betaine active agent, 0.01% to 0.3% α-olefin sulfonate, and the rest is water.

[0055] In one or more preferred embodiments, the amount of the multi-component modified nano-SiO2 particles is 0.2-0.6% of the mass of the foaming agent.

[0056] According to the present invention, the α-olefin sulfonate in the foaming agent can be selected from C 14-16 AOS (carbon chain contains 14 to 16 carbons), which is the most common industrial product of α-olefin sulfonate;

[0057] In one or more preferred embodiments, the amount of α-olefin sulfonate used is 0.05 to 0.1% by mass of the foaming agent.

[0058] In one or more preferred embodiments, the betaine active agent in the foaming agent is at least one of cocamidopropyl betaine, oleamidopropyl betaine, and erucamidopropyl betaine, most preferably oleamidopropyl betaine;

[0059] Preferably, the amount of betaine active agent used is 20-40% of the concentration of α-olefin sulfonate, more preferably 30-35%.

[0060] The technical principles of the present invention are as follows:

[0061] (1) After nano-SiO2 is modified with γ-glycidyloxypropyltriethoxysilane, the groups containing vicinal diols grafted onto the surface of the particles have good water solubility. At the same time, these groups can "bury" the hydroxyl groups on the surface of nano-SiO2 particles, preventing Ca 2+ Mg 2+ The bridging effect on the hydroxyl groups on the surface of SiO2 particles improves the temperature and salt resistance of nano-SiO2 particles.

[0062] (2) The nanoparticles modified in a single step are highly hydrophilic and are not easily distributed to the gas-liquid interface to stabilize the foam; however, after the particles modified in a single step further react with dimethyldiethoxysilane, the water phase wetting angle can be increased to above 40° and the surface tension can be reduced to below 55 mN / m. Such particles themselves have a certain foaming ability.

[0063] (3) The betaine surfactant in the composite surfactant can further improve the surface wetting angle of the chemically modified nanoparticles obtained above by "in situ" modification. Generally speaking, the foaming performance of the nanoparticle surface is best when it is close to neutral wetting. In the above chemical modification process, reducing the amount of modifier 1 and increasing the amount of modifier 2 will increase the water-phase wetting angle of the obtained nanoparticles, but the hydration ability of the nanoparticles will decrease, and thus the stability in water will decrease. From a practical point of view, the surface wetting ability of the particles can only be changed to a limited extent by adding modifier 2. In order to further improve the foaming ability of the nanoparticles, the betaine surfactant is used to further regulate the wettability of the nanoparticle surface. The betaine surfactant is an amphoteric surfactant with an isoelectric point of pH 6.5, that is, the surfactant behaves as a cationic surfactant when the isoelectric point is less than 6.5. Since the pH value of the saturated CO2 aqueous solution is about 3-4, the betaine surfactant is positively charged under this condition and can be adsorbed on the negatively charged nano-SiO2 particle surface, thereby further improving the wetting angle of the nanoparticle surface. This adsorption is a dynamic physical adsorption, and controlling the betaine active agent within a low concentration range will not significantly change the stability of the nanoparticles. (4) The betaine active agent is adsorbed on the surface of the nanoparticles, which can reduce the electrostatic repulsion between the nano-SiO2 particles and the electrostatic repulsion between the nano-SiO2 particles and the α-olefin sulfonate, and promote the above substances to be closely arranged on the gas-liquid surface to form a high-strength interface film. The "multi-faceted" modification of the surface of the nano-SiO2 particles in the present invention, such as chemical modification and physical modification, is the fundamental reason for promoting the adsorption of nano-SiO2 particles on the gas-liquid surface and their close arrangement to form a strong interface film. (5) The synergistic effect of the betaine active agent and the α-olefin sulfonate can reduce the surface tension to below 28mN / m, which is also an important reason for promoting the easy formation and stability of the foam.

[0064] The following specific examples illustrate the performance of the modified nano-SiO2 particles, the betaine active agent and the α-olefin sulfonate composite active agent and the foaming agent constructed therefrom.

[0065] The modified nano-SiO2 particles are named NP-xy, where "x" represents the amount of modifier 1 added is x%, and "y" represents the amount of modifier 2 added is y%.

[0066] The simulated saline used in the evaluation consisted of 2.4×10 4 mg / L NaCl, 0.6×10 4 mg / L CaCl2, and the total salt content is 3×10 4 mg / L. Surface tension was measured by the pull-sheet method in simulated saline at 25°C. The wetting angle was measured by the sitting drop method in simulated saline at 25°C after the nanoparticles were centrifuged and pressed into thin sheets, with decane as the oil phase. The surface dilation modulus was measured using a KRUSS DSA100 in simulated saline at 25°C, with a sinusoidal oscillation signal frequency of 0.1 Hz. The thermal stability of the foaming agent was evaluated at a temperature of 80°C and a water salt content of 3×10 4 The foam performance was evaluated at 80°C, 8 MPa, and 3×10 4 It was carried out under the conditions of mg / L.

[0067] Example 1: Comparison of basic properties of nano-SiO2 particles prepared by adding different amounts of modifier 1

[0068] Nano-SiO2 particles were reacted with 3% to 15% γ-glycidyloxypropyltriethoxysilane to prepare modified nano-SiO2 particles NP-3-0, NP-5-0, NP-10-0 and NP-15-0. The results showed that the modified nano-SiO2 particles had the best thermal conductivity at 80℃ and a salt content of 3×10 4 The stability of the modified nanoparticles in mg / L water was measured, and parameters such as surface tension and wetting angle were determined. The relevant properties were compared with those of the unmodified nanoparticles NP-0-0. The results are shown in Table 1.

[0069] Table 1 Properties of nano-SiO2 particles modified in different single steps

[0070]

[0071] It can be seen that when the amount of Modifier 1 is higher than 10%, the modified particles obtained have good stability in simulated saline. In addition, comparison of parameters such as surface tension and wetting angle shows that the surface properties of the nanoparticles obtained after the first step of modification do not change significantly.

[0072] Example 2: The basic properties of nano-SiO2 particles prepared by fixing the amount of modifier 1 at 10% and comparing the basic properties of nano-SiO2 particles prepared by using different amounts of modifier 2

[0073] The basic and application properties of nano-SiO2 particles NP-10-1, NP-10-2, NP-10-3, and NP-10-5 were compared using a fixed 10% dosage of modifier 1, γ-glycidoxypropyltriethoxysilane, and varying the dosage of modifier 2, dimethyltriethoxysilane. The results are shown in Table 2.

[0074] Table 2 Properties of nano-SiO2 particles modified in different two steps

[0075]

[0076] It can be seen that after the two-step modification, the surface tension of the nanoparticles is significantly reduced and the water-phase wetting angle is increased. A higher amount of dimethyltriethoxysilane (Modifier 2) increases the magnitude of the change in these parameters and improves the foam stability of the prepared particles. However, higher amounts of Modifier 2 result in poor stability of the modified particles. Furthermore, analysis of the foaming properties of the simply modified nanoparticles reveals suboptimal foaming rate and foam stability, which may be related to the high surface tension of the simply modified particles and the limited improvement in the water-phase wetting angle on the particle surface.

[0077] Example 3: Comparison of the synergistic effects of betaine surfactants and α-olefin sulfonates with different carbon chain lengths

[0078] α-olefin sulfonates with carbon chains of 14-16 are currently the longest foaming agents. By leveraging the electrostatic attraction between betaine and α-olefin sulfonates under weak acid conditions, betaine and α-olefin sulfonates can be combined to enhance foaming performance. Table 3 lists the performance of cocamidopropyl betaine LAB, oleamidopropyl betaine OAB, and erucamidopropyl betaine EAB combined with α-olefin sulfonate AOS. Considering the solubility and foaming properties of the system, AOS and OAB combinations in a ratio of 3:1 and 4:1 are the best.

[0079] Table 3 Different betaine active agents and α-olefin sulfonates 1) Compounding performance

[0080]

[0081]

[0082] Example 4: The synergistic foam stabilization effect of the composite system of nano-SiO2 particles and OAB and AOS obtained when the amount of modifier 2 was fixed at 10% was compared.

[0083] Different modified nano-SiO2 particles were compounded with 0.075% AOS and 0.025% OAB to construct foaming agents. The basic properties and application performance of these foaming agents were investigated. The results are shown in Table 4.

[0084] Table 4 Performance of foaming agents composed of different modified particles with 0.075% AOS and 0.025% OAB

[0085]

[0086] It can be seen that the foam stabilization effect of the particles prepared at a high dosage of Modifier 2 is significantly improved. The foaming agents composed of NP-10-2 and NP-10-3 exhibit foam stability six times higher than that of AOS and over nine times higher than that of pure nanoparticles. The performance of the foaming agents composed of NP-10-2 and NP-10-3 is comparable, but the foaming agent composed of NP-10-2 is significantly more economical. The surface dilational modulus measurements show that the system with good foam stabilization has a higher surface dilational modulus, indicating that the nanoparticles and surfactants adsorb and align on the surface, forming a strong surface film.

[0087] Example 5: Comparison of the synergistic foam stabilization effect of NP-10-2 and different surfactants

[0088] In order to analyze the role of surfactants in composite foaming agents, the performance of systems composed of 1% NP-10-2 and different surfactants was compared. The results are shown in Table 5.

[0089] Table 5 Performance of single surfactant and composite surfactant with two-step modified nanoparticles

[0090]

[0091] As can be seen, the foaming performance of the system composed of 1% NP-10-2 and a composite surfactant is significantly better than that of the foaming agent composed of 1% NP-10-2 and a single surfactant. The foaming agent composed of 1% NP-10-2 and AOS performs equally well as AOS alone, indicating that 1% NP-10-2 and AOS do not produce a synergistic effect. This is related to the fact that both NP-10-2 and AOS are negatively charged, making AOS less likely to adsorb on the nanoparticle surface. For the composite system of 0.025% NP-10-2 and 0.025% OAB, although OAB adsorbs on the nanoparticle surface and alters its wettability under weakly acidic conditions, the system's surface tension is relatively high and its surface dilational modulus is relatively low, resulting in suboptimal foam stabilization.

Claims

1. A multi-component modified nano-SiO2 particle, characterized in that: The multi-component modified nano-SiO2 particles are obtained by modifying nano-SiO2 particles with γ-glycidyloxypropyltriethoxysilane and dimethyldiethoxysilane; In the multi-component modified nano-SiO2 particles, the content of γ-glycidyloxypropyltriethoxysilane is 10-15% of the mass of the nano-SiO2 particles, and the content of dimethyldiethoxysilane is 1-3% of the mass of the nano-SiO2 particles.

2. The multi-component modified nano-SiO2 particles according to claim 1, characterized in that: The particle size of the nano-SiO2 is 10-100 nm.

3. The method for preparing the multi-component modified nano-SiO2 particles according to any one of claims 1 to 2, comprising the following steps: (1) Modification step 1: Reaction of nano-SiO2 particles with γ-glycidyloxypropyltriethoxysilane Disperse nano-SiO2 particles in methanol, add γ-glycidoxypropyltriethoxysilane, and heat to 50-70°C for 8-12 hours; (2) Step 2 modification: reaction of the modified product from step 1 with dimethyldiethoxysilane Add dimethyldiethoxysilane to the modified product of step 1 and react at 50-70°C for 8-12 hours to obtain multi-component modified nano-SiO2 particles.

4. The multi-component modified nano-SiO2 particles according to any one of claims 1 to 2 are used in a CO2 foaming agent system in the oil reservoir field.

5. A method for constructing a CO2 foaming agent, comprising compounding the multi-component modified nano-SiO2 particles according to any one of claims 1 to 2 with a betaine active agent and an α-olefin sulfonate.

6. A CO2 foaming agent comprising the multi-component modified nano-SiO2 particles according to any one of claims 1 to 2, comprising the following components in percentage by mass: 0.1%~1% multi-component modified nano-SiO2 particles, 0.01%~0.1% betaine active agent, 0.01%~0.3% α-olefin sulfonate, and the rest is water.

7. The CO2 foaming agent according to claim 6, characterized in that The amount of multi-component modified nano-SiO2 particles in the foaming agent is 0.2-0.6% of the mass of the foaming agent.

8. The CO2 foaming agent according to claim 6, wherein The α-olefin sulfonate in the foaming agent is C 14-16 The dosage of AOS, α-olefin sulfonate is 0.05~0.1% of the mass of the foaming agent.

9. The CO2 foaming agent according to claim 6, characterized in that The betaine active agent in the foaming agent is at least one of cocamidopropyl betaine, oleamidopropyl betaine and erucamidopropyl betaine.

10. The CO2 foaming agent according to claim 6 or 9, characterized in that The dosage of betaine active agent is 20-40% of the concentration of α-olefin sulfonate.

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