CN113214815A

CN113214815A - Nano microemulsion oil displacement agent and preparation method thereof

Info

Publication number: CN113214815A
Application number: CN202110495444.7A
Authority: CN
Inventors: 吴景春; 张春龙; 唐鹏飞; 王力; 崔有明; 李洪岩; 朱健军
Original assignee: Daqing Yongzhu Petroleum Technology Development Co ltd
Current assignee: Daqing Yongzhu Petroleum Technology Development Co ltd
Priority date: 2021-05-07
Filing date: 2021-05-07
Publication date: 2021-08-06
Anticipated expiration: 2041-05-07
Also published as: CN113214815B

Abstract

The invention belongs to the field of chemical oil displacement for improving the recovery ratio of crude oil, and particularly relates to a nano microemulsion oil displacement agent, which consists of water, oil, a surfactant, isopropanol and sodium chloride; wherein the volume ratio of the oil to the water is 0.8-0.9: 1, and the concentration of the surfactant is 2.0-2.5 wt.%, the concentration of the isopropanol is 3.0-8.0 wt.%, and the concentration of the sodium chloride is 2.0-5.5 wt.% based on the total weight of the oil and the water; the surfactant is a combination of polyoxyethylene ether nonionic surfactant (Triton X) and sulfonated saponin. The nano microemulsion oil displacement agent belongs to a middle-phase microemulsion, has small particle size, the size of liquid drops is about 20-50 nm, and the interfacial tension with an oil-water two phase can be reduced to 1.0 multiplied by 10^‑4mN/m is less than, and the crude oil recovery rate can be improved by more than 10 percent compared with water drive.

Description

Nano microemulsion oil displacement agent and preparation method thereof

Technical Field

The invention belongs to the field of chemical oil displacement for improving the recovery ratio of crude oil, and particularly relates to a nano microemulsion oil displacement agent and a preparation method thereof.

Background

With the continuous progress of oil production, many areas of the world have entered the high water and extra high water phases of development. In order to increase the recovery rate of old oil fields and increase the recoverable reserves, tertiary oil recovery is often used to increase the recovery rate of crude oil after water flooding, which is also called Enhanced Oil Recovery (EOR) method, and generally refers to that after secondary oil recovery, the properties of oil, gas, water and rock are improved by injecting chemicals, heat, miscible solvents and other substances, so as to recover more oil.

Four major technological lines of tertiary oil recovery, namely chemical flooding, gas flooding, thermal flooding and microbial oil recovery, have now been developed around the world. Wherein the chemical flooding comprises polymer flooding, surfactant flooding, alkali water flooding and composite flooding technologies.

The polymer can greatly increase the viscosity of the displacement fluid, improve the oil-water fluidity ratio and block a high-permeability layer, so that the polymer is often used for oil displacement to enhance the oil recovery effect. However, the existing chemical flooding technology including polymer flooding is mainly used for medium and low permeability reservoirs with high permeability and large pore throat radius, and is hardly applied to the medium and low permeability reservoirs, mainly because the medium and low permeability reservoirs have the characteristics of low permeability, small pore throat radius, large seepage resistance, high possibility of blockage and the like geologically, the technical problem of 'no-injection and no-extraction' exists on site, and the problem also limits the application of the traditional chemical flooding, so that the utilization degree and the development effect of the medium and low permeability reservoirs are seriously low.

In recent years, microemulsion flooding is used as a novel flooding method, so that the displacement efficiency and the sweep efficiency can reach the maximum limit, a breakthrough result is obtained in tertiary oil recovery of a low-permeability reservoir, and the crude oil recovery rate is greatly improved. Microemulsions are thermodynamically stable, isotropic, low viscosity transparent or translucent dispersions of oil and water that form spontaneously under certain conditions under the action of surfactants and co-surfactants. MicroemulsionThe particle size of the oil deposit is generally 10-100 nm, and the particle size is far smaller than the pore throat radius of a low-permeability oil deposit, so that the phenomenon of throat blockage cannot occur. The microemulsion solution can be mixed and dissolved with oil and water, and the oil-water interfacial tension is greatly reduced. Compared with the upper phase microemulsion and the lower phase microemulsion, the middle phase microemulsion has more remarkable capability of reducing the oil-water interfacial tension, and the interfacial tension can reach 10^-2～10^-5mN/m. The microemulsion has important application value in tertiary oil recovery, and the crude oil recovery rate is generally improved by more than 10 percent.

For example, the Chinese patent CN 110527503A discloses an anion-cation pair nano emulsion oil displacement agent for oil displacement of medium-low permeability oil reservoirs, which has an average particle size of less than 100nm and contains the following components in percentage by mass: 0.01-10% of dispersed phase, 20-50% of anion and cation system surfactant, 10-30% of zwitter-ion surfactant, 0.5-15% of low carbon alcohol and the balance of water. The anion and cation pair nanoemulsion oil displacement agent has the advantages of high surface activity, strong temperature resistance and salt tolerance, low adsorption loss, low use concentration and the like, and can effectively improve the recovery ratio of medium and low permeability oil reservoirs by more than 15%. However, the content of the surfactant in the composition can reach as high as 80 percent, so that the production cost and the final use cost are obviously too high, and the economic benefit is very low.

For example, the Chinese patent CN 105331348A discloses a homogeneous microemulsion oil displacement agent applied to low permeability oil field for improving crude oil recovery and a preparation method thereof, the homogeneous microemulsion oil displacement agent comprises the following components in formula: the volume ratio of oil to water is 1:1, the concentration of each component is represented by the mass percentage concentration of each component in the total amount of the oil and water, the concentration of the compound surfactant is 2-3.5%, the concentration of the cosurfactant is 4.5-11%, and the concentration of the electrolyte is 2.5-8.5%. The oil displacement agent has good thermodynamic stability, strong capability of solubilizing water and oil and ultralow interfacial tension (10) between the oil displacement agent and the oil and the water^-3mN/m), etc., but the performance of reducing the oil-water interfacial tension and the oil displacement efficiency need to be further improved.

Disclosure of Invention

Therefore, the technical problem to be solved by the present invention is to provide a nano microemulsion oil displacement agent with low production cost, which can significantly reduce the oil-water interfacial tension, effectively reduce the capillary force, improve the crude oil fluidity in rock pores, and further significantly improve the recovery ratio.

As a result of earnest and diligent studies to solve the above problems, the inventors of the present invention have found that a nano microemulsion oil-displacing agent having a specific composition can reduce the oil-water interfacial tension to 1.0X 10^-4The mN/m is less than that of the original oil, and the recovery ratio of the original oil can be improved by more than 10 percent compared with water drive.

The technical scheme of the invention is as follows:

a nanometer microemulsion oil displacement agent comprises water, oil, surfactant, isopropanol and sodium chloride; wherein the volume ratio of the oil to the water is 0.8-0.9: 1, and the concentration of the surfactant is 2.0-2.5 wt.%, the concentration of the isopropanol is 3.0-8.0 wt.%, and the concentration of the sodium chloride is 2.0-5.5 wt.% based on the total weight of the oil and the water; the surfactant is a combination of polyoxyethylene ether nonionic surfactant (Triton X) and sulfonated saponin.

The oil is crude oil of oil field, or crude oil diluted by light oil, or C₆-C₁₈The alkane (b) is selected based on the carbon number rule of the equivalent alkane of the crude oil, and is, for example, n-heptane, n-octane, n-nonane, butylcyclohexane, or the like, preferably n-heptane.

To further enhance the unblocking effect, the oil may contain an optional limonene solvent, preferably in an amount of 10-30% by volume of the oil.

The polyoxyethylene ether nonionic surfactant is preferably Triton X-100.

The sulfonated saponin is prepared by the following method:

firstly, contacting saponin with fuming sulfuric acid for sulfonation reaction, wherein a sulfonation reagent is 3-6 h; then alternately washing the mixture for 1 to 2 times by using deionized water and absolute ethyl alcohol, and finally drying the mixture; the drying temperature is 50-80 ℃, and the drying time is 1-3 h.

Wherein the mass ratio of Triton X to sulfonated saponin is 5-8: 1, preferably 6-7: 1, most preferably 6: 1.

the concentration of the surfactant is preferably 2.2 wt.%.

The concentration of the isopropanol is preferably 4.0-7.0 wt.%, more preferably 5 wt.%.

The concentration of sodium chloride is preferably 3.0-5.0 wt.%, more preferably 3.5 wt.%.

The preparation method of the nano microemulsion oil displacement agent comprises the following steps:

1) preparing an emulsion: according to the metering ratio, firstly mixing oil and water and stirring, then adding a surfactant and sodium chloride, and uniformly stirring to obtain an emulsion;

2) preparing microemulsion: adding isopropanol according to the metering ratio, stirring uniformly, and standing to obtain the homogeneous microemulsion.

The inventors of the present application have found that the preparation process of the present invention can significantly reduce the interfacial tension of oil and water, compared to the Shah method, i.e., a microemulsion is obtained by first preparing an emulsification system of oil, surfactant and isopropyl alcohol, and then adding water.

The invention also provides application of the nano microemulsion oil-displacing agent in improving the recovery ratio of the low-permeability reservoir.

Compared with the prior art, the invention has the beneficial effects that:

1. the nano microemulsion oil displacement agent effectively utilizes the synergistic effect of the components by selecting the surfactant with specific composition and taking isopropanol as cosurfactant, thereby leading the oil-water interfacial tension to be reduced to 1.0 multiplied by 10^-4mN/m or less; further effectively improving the oil displacement efficiency and improving the oil recovery ratio by more than 50 percent compared with water drive.

2. The nano microemulsion oil displacement agent belongs to middle-phase microemulsion, and the interfacial tension with oil-water two phases can be reduced to 1.0 multiplied by 10^-4mN/m is less than or equal to, so that the number of capillary tubes can be obviously increased; compared with the traditional upper phase or lower phase microemulsion, the microemulsion has the best oil displacement effect.

3. The nano microemulsion oil displacement agent has large solubilization capacity, and the solubilization capacity on crude oil can reach more than 70%.

4. The nano microemulsion oil displacement agent has small particle size, the size of liquid drops is about 20-50 nm, the nano microemulsion oil displacement agent can permeate to tiny pores of a low-permeability reservoir and enter a nano-scale fine throat and a micro throat, and can communicate channels, improve the fluidity of crude oil, and effectively realize the purposes of displacement, acidification, blockage removal, injection augmentation and the like.

5. The nano microemulsion oil displacement agent can effectively reduce the capillary force, and can reduce the capillary force by at least 50 percent compared with the conventional surfactant; and can reduce or eliminate capillary end effects.

6. The nano microemulsion oil displacement agent can improve the flowback rate of fracturing fluid.

7. The nano microemulsion oil displacement agent has less adsorption capacity on the solid phase surface, and can reach all areas of liquid spread; compared with the conventional surfactant, the adsorption of the rock can be effectively reduced, the low interfacial tension is maintained, and the flowing pressure of the liquid can be reduced.

8. The preparation process of the nano microemulsion oil displacement agent is simple, and the preparation process is environment-friendly and does not cause environmental pollution.

9. The nano microemulsion oil displacement agent has easily obtained raw materials and wide sources, so that the production cost and the use cost of the product are extremely low.

Additional advantages will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The following advantages are realized and attained, particularly in light of the chemical compositions, methods, and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive.

Supplemental definition

The materials, compounds, compositions and components of the present invention may be used in, or may be used in combination with, the methods and compositions of the present invention, or may be used in the practice of the methods and in the preparation of the compositions, or as products resulting from the methods. It is to be understood that when combinations, subsets, interactions, groups, etc. of these materials are disclosed that while specific reference of each and every collective combination and permutation of these compounds may not be explicitly made, each is specifically contemplated and described herein. For example, if an extraction aid component is disclosed and discussed, and a number of alternative solid state forms of that component are discussed, each and every combination and permutation of the possible reference aid components and solid state forms is specifically contemplated unless specifically indicated to the contrary. This concept applies to all aspects of the invention, including but not limited to steps in methods of making and using the disclosed compositions. Thus, if there are a plurality of additional steps that can be performed it is understood that each of these additional steps can be performed by any specific embodiment or combination of embodiments of the disclosed methods, and that each such combination is specifically contemplated and should be considered disclosed.

In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings:

it must be noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include both one and more than one (i.e., two, including two) unless the context clearly dictates otherwise. Thus, for example, reference to "a base" can include a single base, or a mixture of two or more bases, and the like.

Unless otherwise indicated, the numerical ranges in this disclosure are approximate and thus may include values outside of the stated ranges. The numerical ranges may be stated herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the numerical ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

Reference in the specification and concluding claims to parts by weight of a particular element or component in a composition or article refers to the weight relationship between that element or component and any other elements or components in the composition or article, expressed as parts by weight. Thus, in a composition comprising 2 parts by weight of component X and 5 parts by weight of component Y, X and Y are present in a weight ratio of 2:5 and are present in this ratio regardless of whether additional components are included in the composition.

Unless specifically indicated to the contrary, or implied by the context or customary practice in the art, all parts and percentages referred to herein are by weight and the weight percentages of a component are based on the total weight of the composition or product in which it is included.

References to "comprising," "including," "having," and similar terms in this specification are not intended to exclude the presence of any optional components, steps or procedures, whether or not any optional components, steps or procedures are specifically disclosed. For the avoidance of any doubt, unless stated to the contrary, all methods claimed through use of the term "comprising" may include one or more additional steps, apparatus parts or components and/or materials. In contrast, the term "consisting of … …" excludes any component, step, or procedure not specifically recited or recited. Unless otherwise specified, the term "or" refers to the listed members individually as well as in any combination.

Furthermore, the contents of any referenced patent or non-patent document in this application are incorporated by reference in their entirety, especially with respect to definitions disclosed in the art (where not inconsistent with any definitions specifically provided herein) and general knowledge.

Detailed Description

The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices, and/or methods described and claimed herein are made and evaluated, and are intended to be purely exemplary and are not intended to limit the scope of what applicants regard as their invention. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.) but some errors and deviations should be accounted for. Unless otherwise indicated, parts are parts by weight, temperatures are in degrees Celsius or at ambient temperature, and pressures are at or near atmospheric. There are many variations and combinations of reaction conditions (e.g., component concentrations, desired solvents, solvent mixtures, temperatures, pressures, and other reaction ranges) and conditions that can be used to optimize the purity and yield of the product obtained by the process. Only reasonable routine experimentation will be required to optimize such process conditions.

In addition, the instruments, reagents, materials and the like referred to in the following examples are conventional instruments, reagents, materials and the like in the prior art and are commercially available in a normal way unless otherwise specified. The experimental methods, detection methods and the like referred to in the following examples are conventional experimental methods, detection methods and the like in the prior art unless otherwise specified.

Example 1:

a nanometer microemulsion oil displacement agent comprises water, oil, surfactant, isopropanol and sodium chloride; wherein the volume ratio of oil to water is 0.8:1, the concentration of the surfactant is 2.2 wt.%, the concentration of isopropanol is 5.0 wt.%, and the concentration of sodium chloride is 3.5 wt.%, based on the total weight of the oil and water; the surfactant is a combination of Triton X-100 and sulfonated saponin, and the mass ratio of the Triton X-100 to the sulfonated saponin is 6: 1; the oil is n-heptane.

The preparation process comprises the following steps:

1) preparing sulfonated saponin: firstly, contacting saponin with fuming sulfuric acid for sulfonation reaction, wherein a sulfonation reagent is 5 hours; then alternately washing for 1 time by using deionized water and absolute ethyl alcohol, and finally drying; the drying temperature is 60 ℃, and the drying time is 2 h.

2) Preparing an emulsion: according to the metering ratio, firstly mixing oil and water and stirring, then adding surfactant and sodium chloride, and uniformly stirring to obtain emulsion.

3) Preparing microemulsion: adding isopropanol according to the metering ratio, stirring uniformly, and standing to obtain the homogeneous microemulsion.

Example 2

A nanometer microemulsion oil displacement agent comprises water, oil, surfactant, isopropanol and sodium chloride; wherein the volume ratio of oil to water is 0.9:1, the concentration of the surfactant is 2.0 wt.%, the concentration of isopropanol is 6.0 wt.%, and the concentration of sodium chloride is 4.0 wt.%, based on the total weight of the oil and water; the surfactant is a combination of Triton X-100 and sulfonated saponin, and the mass ratio of the Triton X-100 to the sulfonated saponin is 7: 1; the oil is n-heptane.

The preparation method is the same as example 1.

Comparative example 1

A nano microemulsion oil displacement agent, which has basically the same composition as the nano microemulsion oil displacement agent in the embodiment 1, and is only distinguished in that: the oil to water volume ratio was 1: 1.

The preparation method is the same as example 1.

Comparative example 2

A nano microemulsion oil displacement agent, which has basically the same composition as the nano microemulsion oil displacement agent in the embodiment 1, and is only distinguished in that: the concentration of surfactant was 3.0 wt.%.

The preparation method is the same as example 1.

Comparative example 3

A nano microemulsion oil displacement agent, which has basically the same composition as the nano microemulsion oil displacement agent in the embodiment 1, and is only distinguished in that: the mass ratio of Triton X-100 to sulfonated saponin is 4: 1.

the preparation method is the same as example 1.

Comparative example 4

A nano microemulsion oil displacement agent, which has basically the same composition as the nano microemulsion oil displacement agent in the embodiment 1, and is only distinguished in that: the mass ratio of Triton X-100 to sulfonated saponin is 9: 1.

the preparation method is the same as example 1.

Comparative example 5

A nano microemulsion oil displacement agent, which has basically the same composition as the nano microemulsion oil displacement agent in the embodiment 1, and is only distinguished in that: the concentration of isopropanol was 10.0 wt.%.

The preparation method is the same as example 1.

Comparative example 6

A nano microemulsion oil displacement agent, which has basically the same composition as the nano microemulsion oil displacement agent in the embodiment 1, and is only distinguished in that: the surfactant is the combination of Triton X-45 and sulfonated saponin.

The preparation method is the same as example 1.

Comparative example 7

A nano microemulsion oil displacement agent, which has basically the same composition as the nano microemulsion oil displacement agent in the embodiment 1, and is only distinguished in that: n-butanol is used as cosurfactant instead of isopropanol.

The preparation method is the same as example 1.

Comparative example 8

A nano microemulsion oil displacement agent, which has basically the same composition as the nano microemulsion oil displacement agent in the embodiment 1, and is only distinguished in that: the surfactant is a combination of Triton X-100 and saponin.

The preparation method is basically the same as that of example 1, and the steps of saponin sulfonation and sulfonated saponin addition are omitted.

Comparative example 9

A nano microemulsion oil displacement agent, which has basically the same composition as the nano microemulsion oil displacement agent in the embodiment 1, and is only distinguished in that: the surfactant was Triton X-100 only.

The preparation method is basically the same as that of example 1, and the step of adding the sulfonated saponin is omitted.

Comparative example 10

A nano microemulsion oil displacement agent, which has basically the same composition as the nano microemulsion oil displacement agent in the embodiment 1, and is only distinguished in that: the surfactant is only sulfonated saponin.

The preparation method is basically the same as that of example 1, and the step of adding Triton X-100 is omitted.

The particle size of the prepared nano microemulsion oil displacement agent and the interfacial tension between oil and water are respectively inspected according to the following methods, so that the crude oil recovery efficiency is improved.

1. And (3) particle size measurement: and (4) carrying out a scanning electron microscope on the homogeneous microemulsion system, and observing the particle size of the homogeneous microemulsion system.

2. And (3) measuring the interfacial tension between the nano microemulsion oil displacement agent and oil and water: the testing temperature is 75 ℃, the water sample is Daqing oilfield formation water, the oil sample is Daqing oilfield wellhead crude oil, the concentration of the nano microemulsion oil displacement agent is 0.2 wt.%, and the measuring instrument is a American spinning drop interfacial tension meter 500 type.

3. Measurement of enhanced oil recovery capacity: the method comprises the steps of evacuating saturated water from the beret core, saturating crude oil, respectively injecting water and a nano microemulsion oil displacement agent aqueous solution (diluting the nano microemulsion oil displacement agent with water into a 0.5% aqueous solution) into a slug of 0.3PV, driving the beret core until the water content is more than 98%, stopping the test, and respectively recording the water drive recovery ratio and the recovery ratio reached by injecting the nano microemulsion oil displacement agent.

The test results are shown in table 1.

TABLE 1 Performance test results for Nano microemulsion oil displacement Agents

From the test results of the examples 1-2, the nano microemulsion oil displacement agent produced by the invention has smaller particle size, the minimum particle size can be 20-30nm, and the nano microemulsion oil displacement agent can well pass through a nano-scale fine throat and a micro throat; the interfacial tension with oil and water can be reduced to 1.0 x 10^-4The mN/m is lower than the mN/m, and the ultralow oil-water interfacial tension is realized; thereby improving the crude oil recovery ratio by more than 10 percent and improving the crude oil recovery ratio by at least 52 percent compared with water drive.

Comparing the test results of example 1 with those of comparative examples 1 to 5, it can be found that the content of each component constituting the nano microemulsion oil-displacing agent has a significant influence on the performance of the nano microemulsion oil-displacing agent. The present invention, through the ingenious choice of the contents of the components, which is also one of the intelligent contributions of the present invention, unexpectedly finds that the above-mentioned technical problem to be solved by the present invention is solved only by microemulsions within the content range defined by the present invention. And the conventional mixture ratio in the field is adopted, such as the volume ratio of oil to water is 1:1, or even if the dosage of the surfactant and the cosurfactant is increased, the oil displacement performance equivalent to that of the nano microemulsion oil displacement agent with low production cost can not be obtained at the cost of increasing the production cost and the use cost.

Comparing the test results of example 1 with those of comparative examples 6-8, it can be found that the composition of the nano microemulsion oil-displacing agent has a significant effect on the performance of the nano microemulsion oil-displacing agent. The present invention, through the modulation of the microemulsion components, which is another intelligent contribution of the present invention, unexpectedly finds that the technical problem to be solved by the present invention can be solved only by using the microemulsion with the components defined in the present invention. Even minor variations of the components making up the microemulsion, such as the change of Triton X-100 to Triton X-45, the change of isopropanol to n-butanol, and the non-sulfonation of saponins, resulted in significant deterioration of the properties of the nanomicroemulsion oil-displacing agent, which clearly would not be expected by the person skilled in the art.

Comparing the results of the tests of example 1 with those of comparative examples 9-10, it was found that the presence of a synergistic effect of Triton X-100 and the sulfonated saponin, both components constituting the surfactant (which is a further intelligent contribution of the present invention), and the absence of either, resulted in a significant deterioration of the properties of the oil-displacing agent for nanomicroemulsions, which would obviously be unexpected by the skilled person on the basis of the prior art.

It is noted that it is well known in the art that the key to the preparation of a microemulsion is the formulation, the properties of the microemulsion depend primarily on its formulation, and that changes in the nature or amount of any of the components that make up the microemulsion can affect the formation and properties of the microemulsion. The inventor of the present invention has solved the aforementioned technical problems by obtaining a nano microemulsion oil displacement agent formulated as described above through a very arduous and well-known creative effort.

Throughout this disclosure, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the compounds, compositions, and methods described herein.

Various modifications and variations can be made in the compounds, compositions, and methods described herein. Other aspects of the compounds, compositions, and methods described herein will be apparent from consideration of the specification and practice of the disclosed compounds, compositions, and methods. It is intended that the specification and examples be considered as exemplary.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.

Claims

1. A nanometer microemulsion oil displacement agent comprises water, oil, surfactant, isopropanol and sodium chloride; wherein the volume ratio of the oil to the water is 0.8-0.9: 1, and the concentration of the surfactant is 2.0-2.5 wt.%, the concentration of the isopropanol is 3.0-8.0 wt.%, and the concentration of the sodium chloride is 2.0-5.5 wt.% based on the total weight of the oil and the water; the surfactant is a combination of polyoxyethylene ether nonionic surfactant (Triton X) and sulfonated saponin.

2. The nano microemulsion oil-displacing agent of claim 1, which is oilfield crude oil, or crude oil diluted with light oil, or C₆-C₁₈Of (a) an alkane.

3. The nano microemulsion oil displacement agent according to claim 1, wherein the oil contains an optional limonene solvent, preferably in an amount of 10-30% by volume of the oil.

4. The nano microemulsion oil displacement agent according to claim 1, wherein the polyoxyethylene ether nonionic surfactant is Triton X-100.

5. The nano microemulsion oil-displacing agent according to claim 1, wherein the sulfonated saponin is prepared by the following method:

firstly, contacting saponin with fuming sulfuric acid for sulfonation reaction for 3-6 h; then alternately washing the mixture for 1 to 2 times by using deionized water and absolute ethyl alcohol, and finally drying the mixture; the drying temperature is 50-80 ℃, and the drying time is 1-3 h.

6. The nano microemulsion oil displacement agent according to claim 1, wherein the mass ratio of Triton X to sulfonated saponin is 5-8: 1.

7. the nano microemulsion oil displacement agent according to claim 1, wherein the concentration of the surfactant is preferably 2.2 wt.%, the concentration of the isopropanol is preferably 4.0-7.0 wt.%, and the concentration of the sodium chloride is preferably 3.0-5.0 wt.%.

8. The preparation method of the nano microemulsion oil displacement agent according to any one of claims 1 to 7, comprising the following steps:

9. Use of the nano microemulsion oil displacement agent according to any one of claims 1 to 7 or the nano microemulsion oil displacement agent prepared by the preparation method according to claim 8 in enhanced oil recovery.