A low permeability oil reservoir phase microemulsion oil displacement agent and its application

Abstract

The application relates to a low-penetration oil reservoir middle-phase microemulsion oil displacement agent and application thereof. The low-penetration oil reservoir middle-phase microemulsion oil displacement agent comprises the following components in percentage by mass: 0.05-0.3 wt% of an anionic surfactant, 0.05-0.2 wt% of a cationic-nonionic surfactant, and 95-99.9 wt% of water; the cationic-nonionic surfactant comprises alcohol ether sulfonate and / or alcohol ether carboxylate. The low-penetration oil reservoir middle-phase microemulsion oil displacement agent can form stable middle-phase microemulsion under the conditions of low dosage and low permeability, has high oil displacement efficiency, and can greatly improve the oil reservoir recovery degree; solves the problem that it is difficult to form a middle phase in a low-penetration oil reservoir; and the system is easy to dissolve, does not cause phase separation and precipitation, and is easy to prepare and use.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oil and gas field exploitation, and particularly relates to a phase microemulsion oil displacement agent in low-permeability oil reservoirs and application thereof. BACKGROUND

[0002] Low-permeability oil reservoirs are abundant in China and have become the main battlefield of oil development. Compared with medium and high-permeability oil reservoirs, low-permeability oil reservoirs have more complex reservoir properties and more prominent development contradictions. The rock properties are poor, the pore throat is small, and there is a serious Jamin effect. These problems result in low water injection recovery in low-permeability oil fields, low initial productivity of the reservoir, rapid production decline, and a large amount of remaining oil in the ground after water flooding, which cannot be effectively developed. The overall development level of low-permeability oil reservoirs is low, and the calibrated recovery rate is below 20%.

[0003] At present, a considerable part of low-permeability oil reservoirs have entered the high or even ultra-high water cut stage at a low recovery degree, and the problem of invalid circulation is serious, so it is urgent to develop a replacement technology to greatly improve the recovery rate. Low-permeability oil reservoirs usually have strong microscopic heterogeneity and uneven pore distribution, which affects the oil displacement efficiency and sweep efficiency of the oil displacement system. The main technologies for improving the recovery rate of low-permeability oil reservoirs at present include molecular membrane technology, imbibition oil recovery technology, nano injection enhancement technology, surfactant flooding technology, foam flooding technology, and microsphere profile control technology.

[0004] CN112126009A discloses a polyacrylamide microsphere, a nanoemulsion for low-permeability oil reservoir profile control, and a preparation method and application thereof. The microsphere is a copolymer of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, and N,N-methylenebisacrylamide, and the average particle size of the microsphere is 40-120 nm. The emulsion includes the polyacrylamide microsphere and white oil. The polyacrylamide microsphere is a nanoscale microsphere, has good swelling performance, and can be applied to low-permeability oil reservoir profile control. The emulsion uses white oil as the oil phase, and adds tetrasodium ethylenediaminetetraacetate as a dispersant to improve the dispersion uniformity of the polyacrylamide emulsion. The obtained nanoemulsion has small particle size, good fluidity, and good swelling performance, can continuously migrate and block in the pores of low-permeability oil reservoirs, thereby improving the swept volume of injected water and the recovery rate of low-permeability oil reservoirs.

[0005] CN107603582A discloses a high-efficiency foaming agent for air foam oil displacement, which is prepared by mixing the following components in mass percentage: polyether chain segment betaine amphoteric surfactant, alkyl amide propyl dimethyl amine oxide, cationic alkyl polyglycoside, thickening and stabilizing agent, sodium chloride, sodium alkyl sulfate, N-(2-pyridyl) alcohol ether methylene amide, and the balance of water. The foaming agent has strong comprehensive foam performance, corrosion resistance, high salinity resistance, and oil resistance. In the field of oil field production, it can meet the performance requirements of foam oil displacement in low-permeability oil reservoirs.

[0006] However, the above-mentioned technology, although improving the injection capacity and development effect of low permeability reservoir to some extent, and having certain water reduction and oil increasing capacity, still cannot fundamentally solve the problems of expanding swept volume and improving oil displacement efficiency of low permeability reservoir, so it is urgent to develop a new EOR technology suitable for low permeability reservoir. SUMMARY

[0007] In view of the deficiencies of the prior art, the purpose of the present application is to provide a middle phase microemulsion oil displacement agent in low permeability reservoir and its application, which can form stable middle phase microemulsion under low permeability conditions, greatly improve the recovery rate, and has important significance for efficient development of low permeability reservoir.

[0008] To achieve the purpose of the present application, the following technical solutions are adopted:

[0009] In the first aspect, the present application provides a middle phase microemulsion oil displacement agent in low permeability reservoir, the components of the middle phase microemulsion oil displacement agent in low permeability reservoir include, by mass percentage:

[0010] 0.05wt%-0.3wt% of anionic surfactant, 0.05wt%-0.2wt% of anionic-nonionic surfactant, and 95wt%-99.9wt% of water;

[0011] The anionic-nonionic surfactant includes alcohol ether sulfonate and / or alcohol ether carboxylate.

[0012] The middle phase microemulsion oil displacement in low permeability reservoir of the present application can form stable middle phase microemulsion through the cooperation of the above-mentioned surfactants, and there is almost no capillary resistance in the oil displacement process, which can enter the low permeability matrix under the condition of small pressure gradient, has strong displacement capacity for crude oil in fine low permeability pores, greatly reduces the displacement limit of the injection system, and further can greatly improve the oil displacement efficiency and sweep efficiency of low permeability reservoir. In addition, the alcohol ether sulfonate and / or alcohol ether carboxylate and the anionic surfactant are used in the oil displacement agent of the present application, which can make the system not easy to adsorb and stay, and has better stability.

[0013] The amount of the anionic surfactant in the middle phase microemulsion oil displacement agent in low permeability reservoir of the present application can be 0.06wt%, 0.08wt%, 0.1wt%, 0.12wt%, 0.14wt%, 0.16wt%, 0.18wt%, 0.2wt%, 0.22wt%, 0.24wt%, 0.26wt% or 0.28wt% and the like;

[0014] The amount of the anionic-nonionic surfactant can be 0.06wt%, 0.08wt%, 0.1wt%, 0.12wt%, 0.14wt%, 0.16wt% or 0.18wt% and the like;

[0015] The water can be used in an amount of 95.5wt%, 96wt%, 97wt%, 98wt%, 99wt%, 99.2wt%, 99.5wt%, or 99.8wt%, etc.

[0016] Preferably, the anionic surfactant is a carboxylate surfactant and / or a sulfonate surfactant.

[0017] Preferably, the anionic surfactant is a combination of a carboxylate surfactant and a sulfonate surfactant.

[0018] Preferably, the carboxylate surfactant comprises any one or a combination of at least two of an oleate, a stearate, or a ricinoleate.

[0019] Preferably, the carboxylate surfactant comprises any one or a combination of at least two of sodium oleate, potassium oleate, sodium stearate, sodium ricinoleate.

[0020] Preferably, the sulfonate surfactant comprises an alkyl benzene sulfonate and / or an alkyl naphthalene sulfonate.

[0021] Preferably, the sulfonate surfactant comprises any one or a combination of at least two of sodium dodecyl benzene sulfonate, sodium hexadecyl benzene sulfonate, sodium octadecyl benzene sulfonate, sodium dodecyl naphthalene sulfonate, sodium hexadecyl naphthalene sulfonate, or sodium octadecyl naphthalene sulfonate.

[0022] Preferably, the anionic surfactant is a combination of sodium hexadecyl benzene sulfonate, sodium oleate, and sodium stearate.

[0023] Preferably, the mass ratio of the sodium hexadecyl benzene sulfonate, the sodium oleate, and the sodium stearate is (1-2):(0.5-1.5):(0.1-0.5).

[0024] wherein “1-2” can be 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9, etc.

[0025] “0.5-1.5” can be 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, or 1.4, etc.

[0026] “0.1-0.5” can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, or 0.45, etc.

[0027] Preferably, the alcohol ether sulfonate has the following structure:

[0028] R-(EO) i -(PO) j -SO3Na;

[0029] wherein i, j are independently an integer from 20 to 40 (e.g. 21, 23, 25, 28, 30, 32, 35, 37 or 39, etc.); R is selected from C6-C24 alkyl alcohol (e.g. can be C8, C10, C12, C14, C16, C18, C20 or C22, etc.).

[0030] Preferably, the alcohol ether carboxylate salt has the following structure:

[0031] R-(EO) i -(PO) j -CO2Na;

[0032] wherein i, j are independently an integer from 20 to 40 (e.g. 21, 23, 25, 28, 30, 32, 35, 37 or 39, etc.); R is selected from C6-C24 alkyl alcohol (e.g. can be C8, C10, C12, C14, C16, C18, C20 or C22, etc.).

[0033] Preferably, the low permeability oil reservoir phase microemulsion oil displacement agent further comprises 0.05wt%-0.1wt% of polyelectrolyte, for example, can be 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt% or 0.1wt%, etc. in terms of mass percentage.

[0034] The low permeability oil reservoir phase microemulsion oil displacement agent of the present application can reduce the interfacial tension of the system by adding polyelectrolyte and interacting with the two surfactants, thereby achieving the effect of improving the recovery of low permeability oil reservoirs.

[0035] Preferably, the polyelectrolyte is a low molecular weight polyelectrolyte with a molecular weight of 3000-100000, for example, the molecular weight can be 5000, 10000, 30000, 50000, 70000 or 90000, etc.

[0036] Preferably, the polyelectrolyte comprises any one or a combination of at least two of sodium polyacrylate, sodium polymethacrylate, sodium polystyrene sulfonate, sodium polyvinyl sulfonate, polyethyleneimine, polyvinylamine or polyvinylpyridine;

[0037] Preferably, the polyelectrolyte is a combination of sodium polyacrylate and sodium polystyrene sulfonate;

[0038] Preferably, the mass ratio of sodium polyacrylate and sodium polystyrene sulfonate is 1:(0.5-2), for example, can be 1:0.6, 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.6 or 1:1.8, etc.

[0039] Preferably, the water is any one of reinjection water or produced water.

[0040] Specific point values within the above numerical ranges can be selected, and will not be repeated here.

[0041] In a second aspect, the present application provides a method for preparing the low permeability oil reservoir middle phase microemulsion oil displacement agent as described in the first aspect, the method comprising adding an anionic surfactant and a negative-nonionic surfactant into water in sequence, and mixing uniformly to obtain the oil displacement agent.

[0042] Preferably, the mixing also comprises adding a polyelectrolyte.

[0043] Preferably, the mixing is performed in a stirring manner, and the stirring speed is 200-300 r / min, for example, it can be 210 r / min, 230 r / min, 250 r / min, 270 r / min or 290 r / min, etc.

[0044] Specific point values within the above numerical ranges can be selected, and will not be repeated here.

[0045] In a third aspect, the present application provides a use of the low permeability oil reservoir middle phase microemulsion oil displacement agent as described in the first aspect in oil exploitation.

[0046] The low permeability oil reservoir middle phase microemulsion oil displacement agent for oil exploitation of the present application belongs to the middle phase microemulsion displacement technology, which aggregates and displaces crude oil through the solubilization of surfactants, and the oil displacement process almost does not exist capillary resistance, and the oil displacement efficiency and sweep efficiency are greatly improved. Compared with the traditional chemical displacement technology, the middle phase microemulsion system can enter the low permeability matrix under smaller pressure gradient conditions, and has strong ability to mobilize crude oil in fine low permeability pores, greatly reducing the mobilization limit of the injected system, and therefore, has broad application prospects in low permeability oil reservoirs.

[0047] Preferably, the low permeability oil reservoir middle phase microemulsion oil displacement agent is added with inorganic salt during use.

[0048] Preferably, the amount of the inorganic salt is 0.1-2% of the total amount of the low permeability oil reservoir middle phase microemulsion oil displacement agent, for example, it can be 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5% or 1.8%, etc.

[0049] Preferably, the inorganic salt is any one or a combination of at least two of sodium hydroxide, sodium hydroxide, potassium hydroxide, sodium pyrophosphate, sodium metaphosphate, sodium chloride, potassium chloride, calcium chloride or magnesium chloride.

[0050] Compared with the prior art, the present application has the following beneficial effects:

[0051] (1) The middle-phase microemulsion oil displacement agent provided by the application can form stable middle-phase microemulsion under low dosage and low permeability conditions, solving the problem that it is difficult to form a middle phase in low-permeability oil reservoirs;

[0052] (2) The middle-phase microemulsion oil displacement agent provided by the application is easy to dissolve and will not separate and precipitate, and is easy to prepare and use;

[0053] (3) The low-permeability middle-phase microemulsion oil displacement agent provided by the application has high oil displacement efficiency and can greatly improve the recovery degree of an oil reservoir;

[0054] (4) The low-permeability middle-phase microemulsion oil displacement agent provided by the application has a simple preparation process and is easy to realize large-scale industrial production of the product, thereby promoting the popularization and application of the middle-phase microemulsion oil displacement technology in the oil production field. DETAILED DESCRIPTION

[0055] The following examples are used to illustrate the application, but are not used to limit the scope of the application. If a specific technology or condition is not specified in the examples, the technology or condition described in the literature in the field or according to the product manual is used. If the manufacturer of the instrument is not specified, it is a conventional product that can be purchased through a regular channel.

[0056] The following examples and comparative examples are related to some material source information as follows:

[0057] The C12 Guerbet alcohol ether sodium sulfonate (i=25, j=30) and the C12 Guerbet alcohol ether sodium sulfonate (i=15, j=45) are both self-made in the laboratory, and the preparation method refers to the reference “Preparation of C_(16) Guerbet alcohol polyoxyalkylene ether sulfate and study on its interfacial properties”, Chen Qi, et al., Daily Chemical Industry (English and Chinese), Vol. 52, No. 10, 2022, 1055-1061, and the patent “CN201210058204.1, publication date 20120801”.

[0058] The sodium hexadecyl alcohol ether sulfonate (i=20, j=25) and the sodium octadecyl alcohol ether sulfonate (i=30, j=30) are both self-made in the laboratory, and the preparation method refers to “Study on the synthesis of high-purity sodium dodecyl benzene sulfonate”, Cui Lianfu, Shi Lixin, Jan Manli, Liu Cao, et al., Journal of Shenyang University of Chemical Industry, February 1990.

[0059] The remaining raw materials in the examples of the application can be used as long as they are purchased from regular distributors.

[0060] Example 1

[0061] The embodiment provides a low-permeability oil reservoir middle-phase microemulsion oil displacement agent, which comprises, in percentage by mass, 0.1% of sodium hexadecylbenzenesulfonate, 0.075% of sodium oleate, 0.025% of sodium stearate, 0.16% of sodium C12 Guerbet alcohol ether sulfonate (i=25, j=30), 0.04% of sodium polyacrylate and 0.04% of sodium polystyrene sulfonate, and the rest is formation water.

[0062] The preparation method of the low-permeability oil reservoir middle-phase microemulsion oil displacement agent comprises the following steps: sequentially adding sodium hexadecylbenzenesulfonate, sodium oleate, sodium stearate, sodium C12 Guerbet alcohol ether sulfonate, sodium polyacrylate and sodium polystyrene sulfonate into formation water in percentage by mass, and stirring at a rotating speed of 250 r / min for 1 h to obtain the low-permeability oil reservoir middle-phase microemulsion oil displacement agent.

[0063] Embodiment 2

[0064] The embodiment provides a low-permeability oil reservoir middle-phase microemulsion oil displacement agent, which comprises, in percentage by mass, 0.08% of sodium hexadecylbenzenesulfonate, 0.02% of sodium oleate, 0.02% of sodium stearate, 0.2% of sodium octadecyl alcohol ether sulfonate (i=30, j=30), 0.06% of sodium polyacrylate and 0.03% of sodium polystyrene sulfonate, and the rest is formation water.

[0065] The preparation method of the low-permeability oil reservoir middle-phase microemulsion oil displacement agent comprises the following steps: sequentially adding sodium hexadecylbenzenesulfonate, sodium oleate, sodium stearate, sodium C12 Guerbet alcohol ether sulfonate, sodium polyacrylate and sodium polystyrene sulfonate into formation water in percentage by mass, and stirring at a rotating speed of 250 r / min for 1 h to obtain the low-permeability oil reservoir middle-phase microemulsion oil displacement agent.

[0066] Embodiment 3

[0067] The embodiment provides a low-permeability oil reservoir middle-phase microemulsion oil displacement agent, which comprises, in percentage by mass, 0.15% of sodium hexadecylbenzenesulfonate, 0.14% of sodium oleate, 0.01% of sodium stearate, 0.1% of sodium hexadecyl alcohol ether sulfonate (i=20, j=25), 0.02% of sodium polyacrylate and 0.04% of sodium polystyrene sulfonate, and the rest is formation water.

[0068] The preparation method of the low-permeability oil reservoir middle-phase microemulsion oil displacement agent comprises the following steps: sequentially adding sodium hexadecylbenzenesulfonate, sodium oleate, sodium stearate, sodium C12 Guerbet alcohol ether sulfonate, sodium polyacrylate and sodium polystyrene sulfonate into formation water in percentage by mass, and stirring at a rotating speed of 250 r / min for 1 h to obtain the low-permeability oil reservoir middle-phase microemulsion oil displacement agent.

[0069] Embodiment 4

[0070] The present example provides a low permeability oil reservoir middle phase microemulsion oil displacement agent, the difference between the oil displacement agent and example 1 is only that the anionic surfactant in the oil displacement agent does not include sodium stearate, and the reduced amount is distributed to sodium dodecylbenzenesulfonate and sodium oleate according to the original proportion relationship, and the remaining components remain the same as example 1, and the preparation method refers to example 1.

[0071] Example 5

[0072] The present example provides a low permeability oil reservoir middle phase microemulsion oil displacement agent, the difference between the oil displacement agent and example 1 is only that the anionic surfactant in the oil displacement agent does not include sodium stearate, and the reduced amount is distributed to sodium dodecylbenzenesulfonate and sodium oleate according to the original proportion relationship, and the remaining components remain the same as example 1, and the preparation method refers to example 1.

[0073] Example 6

[0074] The present example provides a low permeability oil reservoir middle phase microemulsion oil displacement agent, the difference between the oil displacement agent and example 1 is only that the anionic surfactant in the oil displacement agent does not include sodium stearate, and the reduced amount is distributed to sodium dodecylbenzenesulfonate and sodium oleate according to the original proportion relationship, and the remaining components remain the same as example 1, and the preparation method refers to example 1.

[0075] Example 7

[0076] The present example provides a low permeability oil reservoir middle phase microemulsion oil displacement agent, the difference between the oil displacement agent and example 1 is only that the C12 gilbert alcohol ether sodium sulfonate (i=25, j=30) is replaced by C12 gilbert alcohol ether sodium sulfonate (i=15, j=45) in equal amount, and the remaining components remain the same as example 1, and the preparation method refers to example 1.

[0077] Example 8

[0078] The present example provides a low permeability oil reservoir middle phase microemulsion oil displacement agent, the difference between the oil displacement agent and example 1 is only that the anionic surfactant in the oil displacement agent does not include sodium stearate, and the reduced amount is distributed to sodium dodecylbenzenesulfonate and sodium oleate according to the original proportion relationship, and the remaining components remain the same as example 1, and the preparation method refers to example 1.

[0079] Example 9

[0080] The present example provides a low permeability oil reservoir middle phase microemulsion oil displacement agent, the difference between the oil displacement agent and example 1 is only that the anionic surfactant in the oil displacement agent does not include sodium stearate, and the reduced amount is distributed to sodium dodecylbenzenesulfonate and sodium oleate according to the original proportion relationship, and the remaining components remain the same as example 1, and the preparation method refers to example 1.

[0081] Example 10

[0082] The present example provides a low permeability reservoir middle phase microemulsion oil displacement agent, which is different from example 1 only in that the polyelectrolyte is 0.08% sodium polystyrene sulfonate, and the other components remain the same as in example 1. The preparation method is referred to example 1.

[0083] Comparative example 1

[0084] The present comparative example provides a low permeability reservoir middle phase microemulsion oil displacement agent, which is different from example 1 only in that it does not include anionic surfactant, and the reduced amount is supplemented by anionic-nonionic surfactant, and the other components remain the same as in example 1. The preparation method is referred to example 1.

[0085] Comparative example 2

[0086] The present comparative example provides a low permeability reservoir middle phase microemulsion oil displacement agent, which is different from example 1 only in that it does not include anionic-nonionic surfactant, and the reduced amount is supplemented by anionic surfactant, and the ratio of sodium hexadecyl benzene sulfonate, sodium oleate, and sodium stearate is kept unchanged, and the other components remain the same as in example 1. The preparation method is referred to example 1.

[0087] Test example 1

[0088] The low permeability reservoir middle phase microemulsion oil displacement agents of examples 1-10 and comparative examples 1-2 were tested for interfacial tension by TX500C, and the oil and water used for testing were oil and water from a certain oilfield in Changqing, the testing temperature was 55°C, and the testing time was 2 hours. The results are shown in Table 1.

[0089] Test example 2

[0090] The low permeability reservoir middle phase microemulsion oil displacement agents of examples 1-10 and comparative examples 1-2 were mixed with Changqing crude oil at a volume ratio of 1:1 in a beaker, stirred, and then poured into a graduated tube, and then placed in a 55°C constant temperature oven for standing. It was observed whether the oil displacement agent could form a middle phase microemulsion. The results are shown in Table 1.

[0091] Table 1

[0092]

[0093]

[0094] Test example 3

[0095] The low-permeability oil reservoir middle-phase microemulsion oil displacement agent of examples 1-10 and comparative examples 1-2 is evaluated for enhanced oil recovery effect by oil displacement experiment. The test method is based on the oil industry standard SY / T 6424-2014 to carry out core flooding experiment evaluation. The oil displacement experiment procedure is: core vacuum saturation of formation water - determination of water phase permeability - saturated crude oil to form bound water - water flooding to 98% water cut - injection of middle-phase microemulsion oil displacement agent slug - subsequent conversion to formation water flooding to 98% water cut.

[0096] The results are shown in Table 2.

[0097] Table 2

[0098]

[0099]

[0100] As can be seen from the data in Tables 1 and 2, the low-permeability oil reservoir middle-phase microemulsion oil displacement agent obtained in examples 1-3 can form a middle-phase microemulsion, and the interfacial tension of the oil displacement agent is even smaller, only 8.16 x 10 -4 -2.55 x 10 -3 , and the water side permeability after the oil displacement experiment is above 4.0 mD, the oil saturation is above 65%, and the oil recovery is increased by more than 15% based on a water flooding recovery of 35%-40%, indicating that the low-permeability oil reservoir middle-phase microemulsion oil displacement agent of the present application does not undergo phase separation and precipitation, is easy to prepare and use; and has high oil displacement efficiency, and can greatly improve the oil reservoir recovery degree.

[0101] The applicant states that the low-permeability oil reservoir middle-phase microemulsion oil displacement agent and its application of the present application are illustrated by the above examples, but the present application is not limited to the above detailed process flow, i.e. it does not mean that the present application must rely on the above detailed process flow to be implemented. It should be understood by those skilled in the art that any improvement on the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific methods, etc. all fall within the protection scope and disclosure scope of the present application.

Claims

1. A low permeability reservoir mid-phase microemulsion oil displacement agent, characterized in that: The components of the low permeability reservoir middle phase microemulsion oil displacement agent include, by mass percentage: Anionic surfactant 0.05wt%-0.3wt%, anionic-nonionic surfactant 0.05wt%-0.2wt%, polyelectrolyte 0.05wt%-0.1wt% and water 95wt%-99.9wt%; The anionic-nonionic surfactant includes alcohol ether sulfonate and / or alcohol ether carboxylate; The alcohol ether sulfonate has the following structure: R-(EO) i -(PO) j -SO3Na; wherein i and j are independently integers of 20-40; R is selected from C6-C24 alkyl alcohol; The alcohol ether carboxylate has the following structure: R-(EO) i -(NIGHT) j -CO2Na; wherein i and j are independently integers of 20-40; R is selected from C6-C24 alkyl alcohol; The anionic surfactant is a carboxylate surfactant and / or a sulfonate surfactant; The carboxylate surfactant includes any one of sodium oleate, potassium oleate, sodium stearate, and sodium ricinoleate, or a combination of at least two thereof; The sulfonate surfactant includes any one of sodium dodecylbenzenesulfonate, sodium hexadecylbenzenesulfonate, sodium octadecylbenzenesulfonate, sodium dodecylnaphthalenesulfonate, sodium hexadecylnaphthalenesulfonate or sodium octadecylnaphthalenesulfonate, or a combination of at least two thereof.

2. The low permeability reservoir mid-phase microemulsion oil displacement agent according to claim 1, characterized in that The anionic surfactant is a combination of a carboxylate surfactant and a sulfonate surfactant.

3. The low permeability reservoir mid-phase microemulsion oil displacement agent according to claim 1, characterized in that, The anionic surfactant is a combination of sodium hexadecylbenzenesulfonate, sodium oleate and sodium stearate.

4. The low permeability reservoir mid-phase microemulsion oil displacement agent according to claim 3, characterized in that: The mass ratio of the sodium hexadecylbenzenesulfonate, sodium oleate and sodium stearate is (1-2): (0.5-1.5) (0.1-0.5).

5. The low permeability reservoir middle phase microemulsion oil displacement agent according to claim 1, characterized in that, The polyelectrolyte is a low molecular weight polyelectrolyte with a molecular weight of 3000-100000.

6. The low permeability reservoir mid-phase microemulsion oil displacement agent according to claim 5, characterized in that: The polyelectrolyte includes any one or a combination of at least two of sodium polyacrylate, sodium polymethacrylate, sodium polystyrene sulfonate, sodium polyethylene sulfonate, polyethylene imine, polyethylene amine or polyvinyl pyridine.

7. The low permeability reservoir mid-phase microemulsion oil displacement agent according to claim 6, characterized in that: The polyelectrolyte is a combination of sodium polyacrylate and sodium polystyrene sulfonate.

8. The low permeability reservoir mid-phase microemulsion oil displacement agent according to claim 7, characterized in that: The mass ratio of the sodium polyacrylate to sodium polystyrene sulfonate is 1:(0.5-2).

9. The low permeability reservoir mid-phase microemulsion oil displacement agent according to claim 1, characterized in that: The water is either reinjection water or produced water.

10. Use of the low permeability reservoir middle phase microemulsion oil displacement agent according to any one of claims 1 to 9 in oil production.

11. The use according to claim 10, characterized in that Inorganic salts are added to the low-permeability reservoir middle-phase microemulsion oil-displacing agent during use.

12. The use according to claim 11, characterized in that The amount of the inorganic salt is 0.1-2% of the total amount of the microemulsion oil displacement agent in the low permeability oil reservoir.

13. The use according to claim 11, characterized in that The inorganic salt is any one of sodium hydroxide, sodium hydroxide, potassium hydroxide, sodium pyrophosphate, sodium metaphosphate, sodium chloride, potassium chloride, calcium chloride or magnesium chloride, or a combination of at least two thereof.

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