High strength foam for use in vugular carbonate reservoirs and method of making same

Abstract

The application provides high-strength foam for fractured-vug carbonate reservoirs and a preparation method thereof, and belongs to the technical field of oilfield chemicals, and comprises 0.1-1.5% of a foaming agent, 0.1-1.2% of a foam stabilizer, 5-15% of solid-phase particles, and the balance of liquid preparation water, wherein the sum of the mass percentages of the above components is 100%; the foaming agent is an amphoteric surfactant; the foam stabilizer is modified nanometer carbon dots, and the modified nanometer carbon dots have amphiphilicity; and the solid-phase particles are silica ash. In the application, the amphoteric ionic surfactant rapidly reduces surface tension, drives bubble generation, nanometer particles are adsorbed to the interface to form a primary stable layer, the modified nanometer carbon dots and the amphoteric ionic surfactant synergistically enhance the viscoelasticity of the system, the viscoelastic network dissipates energy through deformation, the rigid particle skeleton resists irreversible deformation, and the foam integrity is synergistically maintained. The silica ash is added to form a rigid adsorption layer, to construct an interface structure with "rigidity and flexibility", and to enhance the foam stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil field chemistry, in particular to high-strength foam for fracture-cave carbonate reservoir and a preparation method thereof. BACKGROUND

[0002] Fracture-cave reservoir is a special type of oil and gas reservoir, mainly composed of fractures and caves as reservoir space and seepage channel, and is a representative type of carbonate reservoir. The fracture-cave size of this type of reservoir varies from several microns to tens of meters, and the distribution is complex and the difference is great.

[0003] The technologies for exploiting remaining oil in fracture-cave reservoir mainly include gas flooding technology, chemical flooding technology, foam flooding technology, profile control and water plugging technology, and physical field assisted technology. Although gas injection can replace the remaining oil at high positions by using gravity differentiation, the gas channeling advantage flow channel is obvious. Although water-gas alternating injection can reduce the influence of gas channeling to some extent and expand the gas action range, the effect is weaker than that in sandstone reservoir. Chemical agents can improve the fluid interface properties and improve the microcosmic oil displacement efficiency, but the fracture-cave reservoir has strong heterogeneity, and the polymer is easy to channel along the large pore channel. The combination of thermal and electromagnetic physical energy can improve the seepage conditions of the reservoir, and is suitable for complex fracture-cave structure, but the technical cost is high. Among the many technologies, foam flooding technology has great potential. Foam flooding technology is to inject gas and surfactant solution into the oil layer in different ways, and use the formed foam as a displacement agent to produce oil. In the fracture-cave reservoir, the foam flooding technology has obvious advantages and can effectively solve the channeling problem of traditional water flooding / gas flooding. It has the characteristics of "reversible plugging" and can release the "attic oil" at the far and near ends. It can effectively displace the remaining oil at the top of the oil layer or the interlayer.

[0004] However, this technology also faces challenges such as significant weakening of the "Jiamin effect" of conventional foam, difficulty in effectively plugging large pore channels, non-uniform migration caused by poor connectivity of fracture-cave, and foam coalescence instability caused by the compression of foam liquid film double layer due to the increase of ionic strength under high-salt conditions. SUMMARY

[0005] In view of the technical problems in the background art, the present application provides a high-strength foam for fracture-cave carbonate reservoir and a preparation method thereof, aiming to solve the technical problem of low stability of foam under high-salt conditions in foam flooding.

[0006] In a first aspect, the embodiments of the present application provide a high-strength foam for fracture-cave carbonate reservoir, which comprises 0.1% to 1.5% of a foaming agent, 0.1% to 1.2% of a foam stabilizer, 5% to 15% of solid particles, and the balance of liquid preparation water, by mass percentage, and the sum of the mass percentages of the above components is 100%.

[0007] The foaming agent is an amphoteric surfactant;

[0008] The foam stabilizer is modified nanometer carbon dots, and the modified nanometer carbon dots have amphiphilicity.

[0009] The solid-phase particles are silica fume.

[0010] In a second aspect, the embodiments of the present application provide a preparation method of high-strength foam for a fractured-vuggy carbonate reservoir, including the following steps:

[0011] S1, dispersing the modified nanometer carbon dots in the liquid preparation water to obtain a carbon dot dispersion liquid;

[0012] S2, adding a foaming agent to the carbon dot dispersion liquid, and after stirring and dissolving, obtaining a mixed liquid;

[0013] S3, adding solid-phase particles to the mixed liquid, and after stirring and dispersing, obtaining a foam liquid;

[0014] S4, foaming the foam liquid in a gas phase to obtain high-strength foam for a fractured-vuggy carbonate reservoir.

[0015] Compared with the prior art, the beneficial effects of the present application include:

[0016] 1. The modified nanometer carbon dots proposed in the present application are hydrophilic-lipophilic carbon dots that can be dispersed in both aqueous and organic phases. Compared with hydrophilic or hydrophobic carbon dots that can only be dispersed in aqueous or organic phases, the modified carbon dots have high surface and interface activity, can significantly reduce the oil-water interfacial tension, can complete self-assembly through hydrophobic interaction, and have the advantage of stronger synergistic effect with surfactants. Compared with ordinary hydrophilic nanometer silica and nanometer titanium dioxide, the modified nanometer carbon dots have more significant thickening effect on the system, reflecting their stronger synergistic thickening effect with amphoteric surfactants.

[0017] 2. The modified nanometer carbon dots proposed in the present application have excellent salt-resistant thickening performance in synergistic effect with the foaming agent. On the one hand, the modified nanometer carbon dots can combine multiple surfactant molecules through hydrophobic interaction, electrostatic attraction and hydrogen bond interaction to connect the dispersed micelles into larger worm-like micelles, and then interweave into a three-dimensional network structure. The surface groups of the modified nanometer carbon dots preferentially combine with salt ions, reducing the shielding effect of salt ions on the charged groups of the foaming agent. On the other hand, the modified nanometer carbon dots can directly participate in micelle formation, and the composite aggregate structure formed with amphoteric surfactants is more compact and has larger steric hindrance, making it difficult for salt ions to enter and destroy the ordered structure.

[0018] 3.The high-strength foam system for the fracture-vug carbonate reservoir has good salt-resistant foam stability, has good foaming performance under high salt (total mineralization is up to 210000 mg / L, and the content of calcium and magnesium ions is greater than 12000 mg / L), and the addition of nano carbon dots and silica ash helps to form a stable rigid film, reduces gas permeation, and enhances foam strength. Overall, the zwitterionic surfactant rapidly reduces the surface tension, drives bubble generation, and nano particles are adsorbed to the interface to form a primary stable layer. Through the synergistic effect of modified nano carbon dots and zwitterionic surfactants, the viscoelasticity of the system is enhanced, the viscoelastic network dissipates energy through deformation, the rigid particle skeleton resists irreversible deformation, and the foam integrity is maintained. The addition of silica ash forms a rigid adsorption layer and constructs an "rigid-flexible" interface structure to enhance the stability of the foam, and the foam stabilizing effect is remarkable. The high-strength foam suitable for the fracture-vug carbonate reservoir has a foaming rate of 350%, and the liquid separation half-life is greater than 20h.

[0019] 4.The high-strength foam suitable for the fracture-vug carbonate reservoir has simple components, is convenient to prepare and use, and has low cost, and is suitable for deep profile control and flooding and foam flooding operations in high water cut reservoirs.

[0020] The above description is only a summary of the technical scheme of the present application, in order to more clearly understand the technical means of the present application, and can be implemented according to the content of the specification, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical scheme of the present application, the following will briefly introduce the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating laborious work.

[0022] Figure 1 Viscosity values of different nanoparticles and foaming agents at different mass fractions.

[0023] Figure 2 The freeze transmission electron microscope photo of the foaming agent solution of the embodiment 1 of the present application. DETAILED DESCRIPTION

[0024] The embodiments of the technical scheme of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical scheme of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application; the description and claims of this application as well as the above abstract are intended to cover all alternatives, modifications, and equivalents thereof in accordance with the scope of the application as defined by the claims. Throughout this application the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0026] The foam flooding process also faces the challenge of significant weakening of the "Jamain effect" of conventional foam under high-salt conditions in ultra-deep fracture-cave type reservoirs, difficulty in effectively plugging large pores, non-uniform migration caused by differences in fracture-cave connectivity, and compression of foam liquid film double layers due to the increase in ionic strength.

[0027] In order to solve the technical problem of low stability of foam under high-salt conditions in foam flooding, the application provides a high-strength foam for fracture-cave type carbonate reservoirs and a preparation method thereof, wherein the zwitterionic surfactant rapidly reduces the surface tension, drives bubble generation, and nanoparticles are adsorbed to the interface to form a primary stable layer. Through the synergistic effect of modified nanocarbon dots and zwitterionic surfactants, the viscoelasticity of the system is enhanced, the viscoelastic network dissipates energy through deformation, the rigid particle skeleton resists irreversible deformation, and the foam integrity is maintained in a synergistic manner. Silica ash is added to form a rigid adsorption layer and construct an "rigid-flexible" interface structure to enhance the stability of the foam, and the foam stabilizing effect is significant.

[0028] In a first aspect, the embodiments of the application provide a high-strength foam for fracture-cave type carbonate reservoirs, which comprises 0.1% to 1.5% of a foaming agent, 0.1% to 1.2% of a foam stabilizer, 5% to 15% of solid particles, and the balance being liquid preparation water, by mass percentage; the sum of the mass percentages of the above components is 100%.

[0029] The foaming agent is a zwitterionic surfactant.

[0030] The foam stabilizer is a modified nanocarbon dot, and the modified nanocarbon dot has amphiphilicity.

[0031] The solid particles are silica ash.

[0032] In the technical solution of the embodiments of the application, the foaming agent selected by the application is a substance that can reduce the surface tension of water and generate a large amount of foam. Its molecular structure has a hydrophilic group and a hydrophobic group, which are arranged in a direction to form a monomolecular film, thereby reducing the surface tension of the gas-liquid interface and making the gas easily dispersed in the liquid to form foam. At the same time, the close arrangement of the foaming agent molecules on the liquid film surface also increases the elasticity and strength of the liquid film, which helps to stabilize the foam.

[0033] The modified nanometer carbon dots selected by the application have a large specific surface area and a high hydrophilic-lipophilic surface energy, and can enhance the viscoelasticity of the system and maintain the stability of the foam through the synergistic effect with the foaming agent.

[0034] The silica ash selected by the application is a kind of mineral powder with certain activity. It can be filled in the liquid film of the foam to increase the thickness and strength of the liquid film and improve the stability of the foam. In addition, the active groups on the surface of the silica ash particles can chemically react or physically adsorb with other components, further enhancing the stability of the foam.

[0035] In some embodiments, the foaming agent includes at least one of a betaine type amphoteric surfactant, an imidazoline type amphoteric surfactant.

[0036] In some embodiments, the betaine type amphoteric surfactant includes at least one of cocamidopropyl betaine, cocamidopropyl hydroxysultaine, lauramidopropyl betaine, lauramidopropyl hydroxysultaine, oleamidopropyl betaine, oleamidopropyl hydroxysultaine, erucamidopropyl betaine, erucamidopropyl hydroxysultaine.

[0037] In some embodiments, the imidazoline type amphoteric surfactant includes at least one of lauryl amphoteric imidazoline, cocoyl amphoteric imidazoline, sodium lauroamphoacetate, sodium cocamphoacetate.

[0038] In some embodiments, the particle size of the modified nanometer carbon dots is 1-10 nm.

[0039] In some embodiments, the preparation method of the modified nanometer carbon dots includes the following steps: dispersing 1.2-1.6 parts of glucose and 2.0-3.0 parts of p-diphenylamine in deionized water, and performing hydrothermal reaction at 160-200℃, and after 10-14h of reaction, dialysis, freeze-drying to obtain the modified nanometer carbon dots.

[0040] In some embodiments, the components of the silica ash include SiO2, Al2O3, FeO, Fe2O3, CaO, MgO, free carbon, K2O and Na2O.

[0041] In some embodiments, the liquid preparation water is high-mineral water, low-mineral water or tap water.

[0042] In some embodiments, the total mineralization of the high-mineral water is 140000-210000mg / L, and the total mineralization of the low-mineral water is 25000-70000mg / L.

[0043] In a second aspect, the embodiments of the application provide a preparation method of high-strength foam for fracture-vug carbonate reservoirs, including the following steps:

[0044] S1, dispersing the modified nanometer carbon dots in the liquid preparation water to obtain a carbon dot dispersion liquid;

[0045] S2, adding a foaming agent to the carbon dot dispersion liquid, and after stirring and dissolving, obtaining a mixed liquid;

[0046] S3, adding solid particles to the mixed liquid, and after stirring and dispersing, obtaining a foaming liquid;

[0047] S4, foaming the foaming liquid in a gas phase to obtain a high-strength foam for a fracture-vug carbonate reservoir.

[0048] In some embodiments, the stirring and dispersing conditions in step S3 are as follows: stirring at a speed of 100-500 r / min for 10-60 min.

[0049] In some embodiments, the gas phase includes one of nitrogen, carbon dioxide, or natural gas.

[0050] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are used to explain the present application, and cannot be understood as limiting the present application. If a specific technology or condition is not specified in the embodiments, it is performed according to the technology or condition described in the literature in the art or according to the product manual. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0051] I. Preparation method

[0052] The nanometer carbon dots used in the following examples were prepared by the following method: 1.50 g of glucose and 2.50 g of p-diphenylamine were placed in a high-temperature and high-pressure reaction kettle, 15.0 mL of distilled water was added, and the reaction was carried out at 180℃ for 12 h; after dialysis, freeze-drying was performed to obtain modified nanometer carbon dots.

[0053] Example 1

[0054] The preparation method of the high-strength foam for the fracture-vug carbonate reservoir includes the following steps: at room temperature (20±5℃), 92.23 g of high mineral water (mineralization degree is 210000 mg / L, prepared in the laboratory) and 0.17 g of nanometer carbon dots are mixed uniformly, then a mechanical stirrer is used to stir at a speed of 500 r / min for 20 min, then 0.6 g of oleic acid amide propyl hydroxyl sulfobetaine foaming agent is added, a mechanical stirrer is used to stir at a speed of 500 r / min for 20 min, then 7.0 g of silica ash is added while stirring, and the mixture is uniformly stirred at 500 r / min for 5 min to prepare a high-strength foam system for the fracture-vug carbonate reservoir. Foaming in the air in a Wu Yin coagulator to obtain a high-strength foam for the fracture-vug carbonate reservoir.

[0055] The foaming volume of the foam at 3000 r / min for 3 min at room temperature was 350 mL, and the liquid drainage half-life was 26 h.

[0056] Examples 2-6 and Examples 8-13

[0057] Examples 2-6 and Examples 8-13 are different from Example 1 in that different foaming agents are used, which are cocamidopropyl betaine (CAB-35), cocamidopropyl hydroxysultaine (CHSB), lauramidopropyl betaine (LAB-35), lauramidopropyl hydroxysultaine (LHSB), oleamidopropyl betaine (OAB), erucamidopropyl betaine (EAB), erucamidopropyl hydroxysultaine (EHSB), lauryl amphoteric imidazoline (LAD), cocamidopropyl imidazoline (CAD), sodium lauroamphoacetate (LAMC), and sodium cocamphoacetate (CAMC).

[0058] The mass fraction of the foaming agent is 0.6%, the mass fraction of the modified nanocarbon dots is 0.17%, the mass fraction of the solid-phase particulate silica ash is 7.0%, and the mass fraction of the remaining liquid high-mineral water is 92.23%. The sum of the mass fractions of the components is 100%. The method for preparing the high-strength foam used for the vugular carbonate reservoir is the same as that in Example 1.

[0059] The types of foaming agents used in Examples 1-6 and Examples 8-13, the bubble volume, and the liquid drainage half-life are shown in Table 1.

[0060]

[0061] Examples 14-15

[0062] Examples 14-15 are different from Example 1 in that the addition amounts of the foaming agents are different. The foaming agent used in Examples 1, 14, and 15 is oleamidopropyl hydroxysultaine (OHSB), and the addition amounts of the foaming agent are 0.6%, 0.4%, and 0.8%, respectively.

[0063] The types of foaming agents used in Examples 1, 14-15, the bubble volume, and the liquid drainage half-life are shown in Table 2.

[0064]

[0065] Examples 16-19

[0066] Examples 16-19 are different from Example 1 in that the addition amounts of the silica ash are different. The addition amounts of the silica ash in Examples 1, 16-19 are 7.0%, 4.0%, 6.0%, 8.0%, and 10.0%, respectively.

[0067] The amount of silica fume, the bubble volume and the half-life of the liquid separation used in Examples 1, 14-15 are shown in Table 3.

[0068]

[0069] Examples 20-21

[0070] Examples 20-21 are different from Example 1 in that the types of the mixing water are different, and the types of the mixing water in Examples 1, 16-19 are high mineral water, low mineral water and tap water, respectively.

[0071] The amount of silica fume, the bubble volume and the half-life of the liquid separation used in Examples 1, 20-21 are shown in Table 4.

[0072]

[0073] Example 22

[0074] Example 22 is different from Example 1 in that the amount of the foaming agent oleic acid amide propyl hydroxyl sulfobetaine (OHSB) is 2%.

[0075] Comparative Examples 1-12

[0076] Comparative Examples 1-12 are different from Examples 2-13 in that only the foaming agent is added, and the weight of the foaming agent, the bubble volume and the half-life of the liquid separation used in Comparative Examples 1-12 are shown in Table 5.

[0077]

[0078] As can be seen from the data in Tables 1 and 5, the bubble energy in Comparative Examples 1-12 is comparable to that in Examples 2-13, but the half-life of the liquid separation is lower than that in Examples 2-13, i.e. the foam prepared by only using the foaming agent has reduced foam stability.

[0079] Comparative Example 13

[0080] Comparative Example 13 is different from Example 1 in that the system is a single modified nanocarbon dot. At room temperature (20±5°C), 92.23 g of high mineral water (210,000 mg / L, prepared in the laboratory) and 0.17 g of carbon dots are mixed uniformly, then stirred at a stirring speed of 500 r / min for 20 min using a mechanical stirrer, and then foamed in a Wu Yin coagulator in air. The foaming volume of this system at room temperature, 3000 r / min and 3 min is 205 mL, and the half-life of the liquid separation is 5 min. The single modified nanocarbon dot has poor effect.

[0081] Comparative Examples 14-25

[0082] Comparative Examples 14-25 are different from Examples 2-13 in that no silica fume is added, and the other preparation methods are the same. The types of foaming agents, bubble volumes, and liquid separation half-lives used in Comparative Examples 14-25 are shown in Table 6.

[0083]

[0084] The experimental results in Tables 1 and 6 show that the foaming capacity of the samples in Comparative Examples 2-13 is comparable to that of Examples 14-25, and the measured liquid separation half-lives are lower than those of Examples 2-13, i.e., the foam stability is lower than that of Examples 2-13, indicating that the silica fume promotes the foam stability of the system.

[0085] Comparative Examples 26-28

[0086] Comparative Examples 26-28 are different from Examples 14-15 in that no silica fume is added to the system, and the weights of foaming agents, bubble volumes, and liquid separation half-lives used in Comparative Examples 26-28 are shown in Table 7.

[0087]

[0088] The experimental results in Tables 2 and 7 show that the foaming capacity and liquid separation half-life of the samples in Comparative Examples 26-28 are lower than those of Examples 14-15, i.e., the foam stability is lower than that of Examples 14-15. The silica fume plays a strong bridging role to maintain foam stability.

[0089] Comparative Examples 29-31

[0090] Comparative Examples 29-31 are different from Examples 20-21 in that no silica fume is added to the system, and the weights of foaming agents, bubble volumes, and liquid separation half-lives used in Comparative Examples 29-31 are shown in Table 8.

[0091]

[0092] The experimental results in Tables 4 and 8 show that the liquid separation half-lives of the samples in Comparative Examples 29-31 are lower than those of Examples 20-21, i.e., the foam stability is lower than that of Examples 20-21. This shows that the silica fume can play a strong foam stabilizing effect in any liquid.

[0093] Comparative Example 32

[0094] Comparative Example 32 is different from Example 1 in that the modified nanocarbon dots are replaced by nanometer SiO2.

[0095] Comparative Example 33

[0096] Comparative Example 33 is different from Example 1 in that the modified nanocarbon dots are replaced by nanometer TiO2.

[0097] II. Test Methods

[0098] Method for detecting the half-life of the separated solution: The systems prepared in each example and comparative example were foamed using a Wu Yin coagulant under the following conditions: room temperature, 3000 r / min, and 3 min. The time required for half the volume of the original solution to separate from the foam was recorded.

[0099] Apparent viscosity measurement: A DVⅢpro viscometer (Brookfield, USA) was used at room temperature and 170 s⁻¹. -1 The apparent viscosity of the solution in the system was measured, and the average value of the three measurements was recorded.

[0100] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0101] (1) The apparent viscosity of the high-strength foams obtained in Example 1 and Comparative Examples 32-33 for fractured-vuggy carbonate reservoirs was measured. The measurement results are as follows: Figure 1 As shown. From Figure 1 As can be seen, the viscosity of SiO2 and TiO2 nanoparticles remains low and fluctuates little regardless of the amount added, while modified carbon nanoparticles can significantly change the viscosity. This indicates that among these three types of nanoparticles, modified carbon nanoparticles have a key impact on the viscosity of the three-phase foam system and can trigger special interactions within the system. Due to their own structure and surface properties, modified carbon nanoparticles easily form networks or adsorption in the system, significantly increasing the system viscosity.

[0102] (2) Figure 2 This is a cryo-transmission electron microscope image of the foaming agent solution from Example 1. Figure 2 The yellow circles indicate the arrangement of modified carbon nanodots along linear micelles, while the red circles indicate the aggregation of modified carbon nanodots at multiple micelle entanglement points, enhancing entanglement strength. The presence of modified carbon nanodots not only increases micelle rigidity and reduces deformation but also strengthens the overall network structure and improves bulk phase properties.

[0103] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A high-strength foam for use in a vugular carbonate reservoir, characterized in that, By mass percentage, 0.1%-1.5% of a foaming agent, 0.1%-1.2% of a foam stabilizer, 5%-15% of solid phase particles, and the balance of liquid preparation water, the sum of the mass percentages of the above components being 100%. The foaming agent is an amphoteric surfactant; the amphoteric surfactant includes at least one of cocamidopropyl betaine, cocamidopropyl hydroxysultaine, lauramidopropyl betaine, lauramidopropyl hydroxysultaine, oleamidopropyl betaine, oleamidopropyl hydroxysultaine, erucamidopropyl betaine, and erucamidopropyl hydroxysultaine. The foam stabilizer is modified nanometer carbon dots, the modified nanometer carbon dots having amphiphilicity; the preparation method of the modified nanometer carbon dots includes the following steps: dispersing 1.2-1.6 parts of glucose and 2.0-3.0 parts of p-diphenylamine in deionized water, performing hydrothermal reaction at 160-200℃, and after 10-14h of reaction, dialysis, freeze-drying, to obtain the modified nanometer carbon dots. The solid phase particles are silica fume, and the components of the silica fume include SiO2, Al2O3, FeO, Fe2O3, CaO, MgO, free carbon, K2O, and Na2O.

2. The high-strength foam for use in a vugular carbonate reservoir according to claim 1, characterized by, The particle size of the modified nanometer carbon dots is 1-10nm.

3. The high-strength foam for use in a vugular carbonate reservoir according to claim 1, characterized by, The liquid preparation water is high-mineral water, low-mineral water, or tap water. The total mineralization of the high-mineral water is 140000-210000mg / L, and the total mineralization of the low-mineral water is 25000-70000mg / L.

4. A method of preparing a high-strength foam for use in a fractured-vug carbonate reservoir according to any one of claims 1 to 3, wherein, The method includes the following steps: S1, dispersing the modified nanometer carbon dots in the liquid preparation water to obtain a carbon dot dispersion liquid; S2, adding the foaming agent to the carbon dot dispersion liquid, stirring and dissolving to obtain a mixed liquid; S3, adding the solid phase particles to the mixed liquid, stirring and dispersing to obtain a foam liquid; S4, foaming the foam liquid in a gas phase to obtain a high-strength foam for a fracture-vug carbonate reservoir.

5. The method for preparing a high-strength foam for use in a vugular carbonate reservoir according to claim 4, characterized by, The stirring and dispersing condition in step S3 is stirring at a speed of 100-500r / min for 10-60min.

6. The method for preparing a high-strength foam for use in a vugular carbonate reservoir according to claim 4, characterized by, The gas phase includes one of nitrogen, carbon dioxide, or natural gas.

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